The Provider Primer Series: Mediator testing

Evidence of mediator release

  • Mast cells produce a multitude of mediators including tryptase, histamine, prostaglandin D2, leukotrienes C4, D4 and E4, heparin and chromogranin A[i].
  • Objective evidence of mast cell mediator release is required for diagnosis of MCAS (Castells 2013)[ii], (Akin 2010)[iii], (Valent 2012)[iv].
  • Serum tryptase and 24 hour urine testing for n-methylhistamine, prostaglandin D2, prostaglandin 9a,11b-F2 are frequently included in MCAS testing recommendations (Castells 2013)[ii], (Akin 2010)[iii], (Valent 2012)[iv].
  • It can be helpful to test for other mast cell mediators including 24 hour urine testing for leukotriene E4[v]; plasma heparin[ix]; serum chromogranin A[ix]; and leukotriene E4[ix].


  • Tryptase is extremely specific for mast cell activation in the absence of hematologic malignancy or advanced kidney disease. Of note, rheumatoid factor can cause false elevation of tryptase[ix].
  • Serum tryptase levels peak 15-120 minutes after release with an estimated half-life of two hours[vi].
  • Per key opinion leaders, tryptase levels should be drawn 15 minutes to 4 hours after onset of anaphylaxis or activation event (Castells 2013[ii]), (Akin 2010[iii]), (Valent 2012)[iv]). Phadia, the manufacturer of the ImmunoCap® test to quantify tryptase, recommends that blood be drawn 15 minutes to 3 hours after event onset[vii].
  • Serum tryptase >11.4 ng/mL is elevated[i]. In addition to measuring tryptase level during the event, another sample should be drawn 24-48 hours after the event, and a third sample drawn two weeks later. This allows comparison of event tryptase level to baseline[vi].
  • An increase in serum tryptase level during an event by 20% + 2 ng/mL above patient baseline is often accepted as evidence of mast cell activation[v],[i].
  • Absent elevation of tryptase level from baseline during an event does not exclude mast cell activation[viii].
  • Sensitivity for serum tryptase assay in MCAS patients was assessed as 10% in a 2014 paper[ix].
  • A recent retrospective study of almost 200 patients found serum was elevated in 8.8% of MCAS patients[x].
  • Baseline tryptase >20.0 ng/mL is a minor criterion for diagnosis of systemic mastocytosis. 77-85% of SM patients have baseline tryptase >20.0 ng/mL[ix].

Histamine and degradation product n-methylhistamine

  • N-methylhistamine is the breakdown product of histamine.
  • Histamine is degraded quickly. Samples should be drawn within 15 minutes of episode onset[vii].
  • Serum histamine levels peak 5 minutes after release and return to baseline in 15-30 minutes[vii].
  • Sample (urine or serum) must be kept chilled[xi].
  • In addition to mast cells, histamine is also released by basophils. Consumption of foods or liquids that contain histamine can also inflate the level when tested[ix].
  • A recent retrospective study of almost 200 patients found that n-methylhistamine was elevated in 7.4% of MCAS patients in random spot urine and 5.4% in 24-hour urine[xi].
  • Sensitivity of 24-hour n-methylhistamine for MCAS was assessed as 22% in 24-hour urine[ix].
  • Plasma histamine was elevated in 29.3% of MCAS patients[xi].
  • 50-81% of systemic mastocytosis patients demonstrate elevated n-methylhistamine in 24-hour urine[ix].

Prostaglandin D2 and degradation product prostaglandin 9a,11b-F2

  • 9a,11b-prostaglandin F2 is the breakdown product of prostaglandin D2.
  • Prostaglandin D2 is only produced in large quantities by mast cells. Basophils, eosinophils and other cells produce minute amounts[ix].
  • A recent retrospective study of almost 200 patients found that PGD2 was elevated in 9.8% of MCAS patients in random spot urines and 38.3% in 24-hour urine[xi].
  • PGD2 was elevated in 13.2% of MCAS patients in plasma[xi].
  • 9a,11b-PGF2 was elevated in 36.8% in 24-hour urine[xi].
  • 62-100% of systemic mastocytosis patients demonstrate elevated prostaglandin D2 or 9a,11b-PGF2 in urine[ix].
  • Prostaglandins are thermolabile and begin to break down in a minutes. This can contribute to false negative results[xi].
  • Medications that inhibit COX-1 and COX-2, such as NSAIDs, decrease prostaglandin production[xi].

Leukotriene E4

  • Leukotriene E4 is produced by mast cells and several other cell types[ix] including eosinophils, basophils and macrophages.
  • A recent retrospective study of almost 200 patients found that LTE4 was elevated in 4.4 % of MCAS patients in random spot urines and 8.3% in 24-hour urine[xi].
  • 44-50% of systemic mastocytosis patients demonstrate elevated leukotriene E4 in urine[ix].
  • Medications that inhibit 5-LO, such as lipoxygenase inhibitors, decrease leukotriene production[xii].

Chromogranin A

  • Chromogranin A is produced by mast cells and several other cell types including chromaffin cells and beta cells.
  • Proton pump inhibitors can cause increased values during testing[xi].
  • A 2014 paper reported chromogranin A was elevated in 12% of MCAS patients and 63% of systemic mastocytosis patients tested[ix].


  • Heparin is a very specific mediator for mast cell activation[ix].
  • Heparin is extremely heat sensitive. The sample must be kept on ice or refrigerated at all times[ix].
  • Venous occlusion of upper arm for ten minutes has been successful in provoking mast cell activation leading to heparin release[ix].
  • A 2014 paper reported plasma heparin was elevated in 59% of MCAS patients and 47% of systemic mastocytosis patients tested[ix].
  • A recent retrospective study of almost 200 patients found that plasma heparin was elevated in 28.9% tested[ix].



[i] Theoharides TC, et al. (2012). Mast cells and inflammation. Biochimica et Biophysica Acta (BBA) – Molecular Basis of Disease, 1822(1), 21-33.

[ii] Picard M, et al. (2013). Expanding spectrum of mast cell activation disorders: monoclonal and idiopathic mast cell activation syndromes. Clinical Therapeutics, 35(5), 548-562.

[iii] Akin C, et al. (2010). Mast cell activation syndrome: proposed diagnostic criteria. J Allergy Clin Immunol, 126(6), 1099-1104.e4

[iv] Valent P, et al. (2012). Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal. Int Arch Allergy Immunol, 157(3), 215-225.

[v] Lueke AJ, et al. (2016). Analytical and clinical validation of an LC-MS/MS method for urine leukotriene E4: a marker of systemic mastocytosis. Clin Biochem, 49(13-14), 979-982.

[vi] Payne V, Kam PCA. (2004). Mast cell tryptase: a review of its physiology and clinical significance. Anaesthesia, 59(7), 695-703.

[vii] Phadia AB. ImmunoCAP® Tryptase in anaphylaxis. Retrieved from:

[viii] Sprung J, et al. (2015). Presence or absence of elevated acute total serum tryptase by itself is not a definitive marker for an allergic reaction. Anesthesiology, 122(3), 713-717.

[ix] Vysniauskaite M, et al. (2015). Determination of plasma heparin level improves identification of systemic mast cell activation disease. PLoS One, 10(4), e0124912

[x] Zenker N, Afrin LB. (2015). Utilities of various mast cell mediators in diagnosing mast cell activation syndrome. Blood, 126(5174).

[xi] Afrin LB. “Presentation, diagnosis and management of mast cell activation syndrome.”  Mast Cells, edited by David B. Murray, Nova Science Publishers, Inc., 2013, 155-231.

[xii] Hui KP, et al. (1991). Effect of a 5-lipoxygenase inhibitor on leukotriene generation and airway responses after allergen challenge in asthmatic patients. Thorax, 46, 184-189.

The Provider Primer Series: Diagnosis and natural history of systemic mastocytosis (ISM, SSM, ASM)

Systemic mastocytosis (SM) is a primary hematologic disorder marked by the excessive proliferation of mast cells.

Neoplastic nature of mastocytosis:

  • Mast cells produced in this disease are neoplastic and may have some or all of the following markers: presence of somatic gain-of-function mutation at codon 816 of CKIT (KIT), usually, but not always, the D816V mutation; expression of CD2 or CD25 on mast cell surface; atypical spindled morphology of mast cells[i].
  • Mastocytosis is a neoplastic condition that is not described exclusively by excessive population of mast cells. Mast cell hyperplasia can occur in response to a number of conditions including chronic urticaria[ii], irritable bowel syndrome[iii], and other hematologic neoplasia, including chronic lymphocytic leukemia, non-Hodgkin lymphoma, and myeloproliferative conditions[iv].
  • To meet criteria for SM, mast cell infiltration must be dense with at least 15 mast cells per cluster. In many instances, there is not a validated range of mast cells/hpf in healthy controls[iv].
Table 1: Diagnostic criteria for systemic mastocytosis[v]

1 major and 1 minor criterion; or 3 minor criteria

Major Multifocal dense infiltrates of mast cells (15 or more in aggregate) detected in sections of bone marrow and/or extracutaneous organ
Minor In biopsy sections, more than 25% of mast cells in infiltrated space are spindle-shaped or otherwise morphologically abnormal; or, of all mast cells in bone marrow aspirate smears, more than 25% mast cells are immature or abnormal. Detection of CKIT mutation at codon 816 in bone marrow, blood or extracutaneous organ Mast cells in bone marrow, blood or other extracutaneous organ that co-expresses CD-117 with CD2 and/or CD25 Baseline serum tryptase of 20 ng/ml or higher.


Presence of dense infiltrates:

  • The hallmark sign of systemic mastocytosis is multifocal dense infiltration of an organ that is not the skin. Despite this fact, it is possible to biopsy negative while still having SM. A 2004 study reported the pathological findings of bilateral bone marrow biopsies for 23 patients. 83% of patients demonstrated positive biopsy for SM bilaterally while 17% of patients had only one positive biopsy[vi].
  • One study found that 20% of ISM patients did not have dense infiltration of mast cells in bone marrow[vii].

Tryptase level in systemic mastocytosis:

  • Tryptase ≥20 ng/mL is a minor criterion for SM. In order to meet this criterion, tryptase must be ≥20 ng/mL at baseline, not during or following a reactive or anaphylactic event. Per Phadia, producer of ImmunoCAP® Tryptase test, it can take up to fourteen days for tryptase to return to baseline[viii]. However, other sources recommend shorter time to baseline, as low as “24 hours after clinical signs and symptoms have completely subsided”[ix].
  • 20-30% of SM patients do not meet the minor criterion of tryptase level ≥20 ng/mL[xiii].

Detection of CKIT D816V mutation:

  • The CKIT D816V mutation may not be detected in peripheral blood in a positive patient. Bone marrow aspirate is the preferred sample type for reliable testing for this mutation[xii].
  • One study reported as few as 78% of ISM patients were positive for the CKIT D816V mutation in bone marrow[xiii].

Natural history of indolent systemic mastocytosis:

  • Indolent systemic mastocytosis (ISM) is SM that does not meet criteria for smoldering systemic mastocytosis, aggressive systemic mastocytosis or mast cell leukemia.
  • ISM is largely described by mediator release symptoms and increased risk of anaphylaxis. Mast cell infiltration does not cause appreciable organ dysfunction in this variant[x].
  • Progression from ISM to SSM occurred in about 8% of patients in a cohort of 74. In this same cohort, 4% ISM patients progressed to ASM[xi]. The risk of leukemic transformation from ISM was 0.6% in a cohort of 159[xii].
  • Organomegaly can present without loss of function at any level of hematologic disease in SM. Organ swelling may be stable over long periods of time without progression to aggressive systemic mastocytosis (ASM)[x].
  • Lifespan for indolent systemic mastocytosis is normal[x].
Table 2: Diagnostic criteria for smoldering systemic mastocytosis

 (2 or 3 B findings in addition to meeting criteria for systemic mastocytosis)[i]

B findings Increased mast cell burden (>30% mast cell aggregates on bone marrow biopsy and/or serum tryptase >200 ng/mL) Hypercellular marrow, signs of myelodysplasia or myeloproliferation in absence of MDS or MPN Organ swelling without deficit of organ function (hepatomegaly without ascites, palpable splenomegaly, lymphadenopathy >2 cm)


Natural history of smoldering systemic mastocytosis:

  • Smoldering systemic mastocytosis (SSM) is defined by increased systemic mast cell burden, presence of markers associated with progression toward ASM (B findings), and potential need for cytoreduction[xiii].
  • SSM can remain stable for many years, even decadesix. In a cohort of 22 patients with SSM, 1 transformed to acute leukemia and 3 progressed to ASM[xiv].
  • Lifespan may be shortened in SSM. A widely reported study found an average lifespan of 10 years but reported that death was often unrelated to mastocytosis and in some cases was of natural old age[xiii].
Table 3: Diagnostic criteria for aggressive systemic mastocytosis

(1 or more C finding in addition to meeting criteria for systemic mastocytosis)[i]

C findings One or more cytopenias (absolute neutrophil count <1000/µl; Hemoglobin <10g/dl; platelets <100000/µl) Hepatomegaly with ascites, elevated liver enzymes with or without portal hypertension Splenomegaly with hypersplenism Malabsorption evidenced by low albumin and weight loss Large osteolysis and/or severe osteoporosis and pathologic fractures (2 or more fractures as direct result of mast cell activity)


Natural history of aggressive systemic mastocytosis:

  • Aggressive systemic mastocytosis (ASM) is defined by significant organ damage and failure as a direct result of mast cell infiltrationxv. Lifespan is often significantly shortened and can be as short as three years[ix] .
  • ASM generally follows one of two paths: a slow progressing form that resembles SSM but has C findings; or a rapidly progressing form that resembles mast cell leukemia. In rapidly progressing ASM, the patient may lose the CKIT D816V mutation[ix] .
  • ASM is managed with cytoreduction but patient response is often short lived. Tyrosine kinase inhibitors and other kinase inhibitors are also used in this population[ix] .
  • In treatment resistant cases, hematopoietic stem cell transplant offers an experimental option. One study on HSCT in advanced systemic mastocytosis included seven ASM patients. 3 (43%) achieved complete remission; 3 (43%) demonstrated progression free survival at the three year mark[xv].


[i] Arber DA, et al. (2016). The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood, 127(20), 2391-2405.

[ii] Minnei F, et al. (2006). Chronic urticaria is associated with mast cell infiltration in the gastroduodenal mucosa. Virchows Arch, 448(3), 262-268.

[iii] Guilarte M, et al. Diarrhoea-predominant IBS patients show mast cell activation and hyperplasia in the jejunum. Gut, 56, 203-209.

[iv] Hamilton MJ, et al. (2011). Mast cell activation syndrome a newly recognized disorder with systemic clinical manifestations. J Allergy Clin Immunol, 128, 147-152.

[v] Molderings GJ, et al. (2011). Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. Journal of Hematology & Oncology, 4(10), 10.1186/1756-8722-4-10

[vi] Butterfield JH, Li, CY. (2004). Bone marrow biopsies for the diagnosis of systemic mastocytosis: is one biopsy sufficient? Hematopathology, Am J Clin Pathol, 121: 264-267.

[vii] Sanchez-Munoz L, et al. (2011). Evaluation of the WHO criteria for the classification of patients with mastocytosis. Mod Pathol, 24(9), 1157-1168.

[viii] Phadia AB. ImmunoCAP® Tryptase: Clinical utility of Total Tryptase. Retrieved from:

[ix] Schwartz LB. (2006). Diagnostic value of tryptase in anaphylaxis and mastocytosis. Immunology and Allergy Clinics of North America, 26(3), 451-463.

[x] Valent P, et al. (2010). How I treat patients with advanced systemic mastocytosis. Blood, 116(26), 5812-5817.

[xi] Matito A, et al. (2013). Serum tryptase monitoring in indolent systemic mastocytosis: association with disease features and patient outcome. PLoS One, 8(10), e76116.

[xii] Lim KH, et al. (2009). Systemic mastocytosis in 342 consecutive adults: survival studies and prognostic factors. Blood, 113(23), 5727-5736.

[xiii] Pardanini A. (2013). How I treat patients with indolent and smoldering mastocytosis (rare conditions but difficult to manage). Blood, 121, 3085-3094.

[xiv] Pardanini A. (2010). WHO subvariants of indolent mastocytosis: clinical details and prognostic evaluation in 159 consecutive adults. Blood, 115, 150-151.

[xv] Ustun C, et al. (2014). Hematopoietic stem-cell transplantation for advanced systemic mastocytosis. J Clin Oncol, 32(29), 3264-3274.

[xvi] Pardanini A. (2013). Systemic mastocytosis in adults: 2013 update on diagnosis, risk stratification, and management. American Journal of Hematology, 88(7, 612-624).

[xvii] Valent P, et al. (2003). Aggressive systemic mastocytosis and related mast cell disorders: current treatment options and proposed response criteria. Leuk Res, 27(7), 635-641.

Take home points: October 2015

Childhood mastocytosis: Update

  • Cutaneous mastocytosis in children is the most common form of mastocytosis
  • True systemic mastocytosis is very rare in children
  • An NIH study of 105 children found 30-65% improved over time
  • Elevated baseline tryptase level and organ swelling were good indicators of SM
  • Serum tryptase should be measured every 6-12 months
  • Children with swelling of both liver and spleen were positive for CKIT D816V mutation
  • Swelling of liver and spleen together was linked to disease persisting into adulthood
  • Most children with UP with skin and minor GI issues had normal tryptase
  • Diffuse cutaneous mastocytosis patients had a much higher average tryptase but no organ swelling
  • Serum tryptase and IgE were inversely related (high tryptase with low IgE, low tryptase with high IgE)

Chronic mast cell leukemia: a new variant of systemic mastocytosis

  • Mast cell leukemia (MCL) has a significantly shortened lifespan
  • Usually over 20% of nucleated cells in bone marrow are atypical mast cells
  • Mast cells are present in large quantities on the blood
  • Cases where less than 10% of white blood cells in blood are mast cells are called aleukemic variant MCL
  • Cases where over 20% of nucleated cells in bone marrow are mature mast cells are called chronic MCL
  • Chronic MCL patients do not have any C findings (the clinical markers for SM patients associated with very aggressive disease)
  • Chronic MCL patients have stable disease state but can progress to acute MCL at any time
  • Mediator release symptoms are more common in chronic MCL than acute MCL
  • Acute MCL is marked by immature CD25+ mast cells
  • Acute MCL patients do have C findings (the clinical markers for SM patients associated with very aggressive disease)
  • Acute MCL has a very short survival time, usually less than a year

Patient questions: Why isn’t tryptase used to track SM progression in patients with SM-AHNMD?

Tryptase can be a useful tool for measuring progression of systemic mastocytosis. However, it is not used in patients with systemic mastocytosis with associated clonal hematologic non-mast cell lineage disease (SM-AHNMD). Patients with SM-AHNMD have systemic mastocytosis and also have another blood disorder that causes excessive proliferation of cells that aren’t mast cells. It is essentially having individual diseases that affect the bone marrow.

The reason tryptase is not tracked in patients with SM-AHNMD is because other proliferative diseases of bone marrow can increase production of mast cells. (Actually, proliferative diseases in most organs can cause increased production of mast cells). This is called mast cell hyperplasia, overproduction of mast cells. It is NOT the same as SM. A patient with no mast cell disease of any kind who has a blood disorder like chronic myelogenous leukemia or essential thrombocythemia could experience an increase in mast cells. It is not uncommon for people with conditions like this to experience allergic symptoms due to mast cell activation.

This can occur for a few reasons. The blood disorder might increase the amount of cells that could become mast cells. The blood disorder could cause increased release and production of molecules that encourage mast cell development. Mast cells are also part of the immune response and heavily involved in tumor biology. Proliferation of another cell type can be interpreted by the body as tumor formation so more mast cells can be made to address the “tumor”, whether or not it actually is a tumor..

A patient with SM-AHNMD may have a baseline tryptase before developing the second blood disorder of 30 ng/mL. (Just making up a number here). After diagnosis with the second blood disorder, a tryptase test could reveal an increase to 35 ng/mL. However, if this were the case, we wouldn’t know if the additional tryptase is coming from mast cells made by SM ramping up or as a side effect of the other blood disorder. Because we can’t tell, it isn’t used as an indicator of increased mast cell production as a direct cause of SM.

For patients with SM-AHNMD, other markers are used to track disease progression of SM. That includes checking for things like inappropriate blood cell counts and organ swelling and dysfunction (B and C findings).

Patient questions: Everything you wanted to know about tryptase

I get a lot of questions about tryptase.

Tryptase is one of the most well characterized mast cell mediators and the first to be unique to mast cells. Serum tryptase is the most well known test for systemic mastocytosis and anaphylaxis. But mast cell patients sometimes test negative, complicating their lives and care.

There are a lot of reasons why mast cell patients test negative for tryptase. One reason is that a lot of the understanding of anaphylaxis hinged upon the ability of mediators to get quickly to the bloodstream to quickly spread to various organ systems. While this does happen, not all mediators move at the same speed. Tryptase is released from granules as large complexes with other mediators, like heparin. It takes time for it to dissociate enough to be active.

Tryptase also does a lot of things and breaks down lots of things. If there are things for it to break down in the immediate environment, it will still break them down whether or not you are having anaphylaxis. Eventually, the tryptase that wasn’t used up breaking things down gets to the bloodstream. This is why the ideal time to test for tryptase in blood is about 90-120 minutes after an allergic event/severe reaction/anaphylaxis. Following severe reaction/anaphylaxis, it can take about two weeks for tryptase to return to baseline.

The reason that most patients with systemic mastocytosis have high tryptase levels is because they have more mast cells and many mast cells secrete tryptase at rest. This means that even if they aren’t activated, they will still release tryptase regularly. The reason why baseline tryptase level is such an important marker for SM is because it distinguishes mastocytosis from anaphylaxis.

However, we have learned a lot about tryptase in the last several years, and it doesn’t seem like all mast cells secrete tryptase all the time. Mast cells are heavily influenced by their environment and the cells around them. Some mast cells make more tryptase than others and some release tryptase regularly and some don’t.

About 80-90% of SM patients have a baseline tryptase over 20 ng/ml. This means they tested over 20 ng/ml on two separate occasions when they had not recently had a severe event. But not all SM patients have elevated tryptase, but that doesn’t mean they don’t have more mast cells than usual. It is possible that their mast cells are concentrated in places in the body where tryptase will be used up before it gets to the bloodstream or that it will take too long to get there for the test to catch it. There is some evidence that tryptase testing is less reliable in overweight and obese women, and I’m sure that’s true. Some mast cells live in adipose tissue and that tissue is harder for large molecules to move through, like tryptase.

Our understanding of MCAS is that there is aberrant mast cell behavior without an abnormal number of mast cells. These patients generally have repeat negative biopsies and so the assumption is that they definitely don’t have SM. But tryptase is a crummy test and I think as a community we can’t really know if they have too many mast cells until we have more robust tests. I’m not saying MCAS patients have too many mast cells, but I’m saying I don’t really trust tryptase for detection of reaction/anaphylaxis in MCAS patients or, to be frank, in anyone.

So why do we still use tryptase if it’s a crummy test? It’s not a crummy test for everything. In particular, it is a very good indicator of disease progression (ISM to SSM to ASM) in patients who have a lot of mast cells. A steadily increasing tryptase level means that there is increased proliferation and can indicate moving to a state where organ damage is more likely. So it is helpful for those people. It’s not helpful for everyone else.

Tryptase testing is not affected in a meaningful way by any medications that I can think of. Mast cell stabilizers can decrease degranulation, but tryptase can also be released in other ways, and there has not been any demonstration that mast cell stabilizers are effective enough to affect this test. Antihistamines/other meds/steroids don’t affect tryptase level.

There was a consensus paper that came out several years ago in which it was posited that an increase in tryptase level of 2 ng/ml + 2% from baseline was indicative of mast cell activation and could be used in the diagnosis of MCAS. This is not widely agreed to in the US and the data supporting this has never been published so I personally understand the reluctance of providers to acknowledge this as a marker of mast cell activation.

The other big reason why mast cell patients may test normal for tryptase is that their reactions/anaphylaxis are not mediated by a pathway that triggers tryptase release like IgE does.  IgG activation and other pathways do not always demonstrate tryptase release.

I think I got everything. If you have more questions about tryptase, let me know.

Kounis Syndrome: Subtypes and effects of mast cell mediators (Part 1 of 4)

Kounis Syndrome (KS) is an acute coronary syndrome that arises as a direct result of mast cell degranulation during an allergic or anaphylactic reaction.

KS usually presents as chest pain during an acute allergic or anaphylactic reaction. There are three recognized variants:

Type I: Patient has no predisposing coronary artery disease.

There are two possible outcomes:

  • Coronary artery spasm with no appreciable increase in cardiac enzymes or troponins
  • Coronary artery spasm that evolves to acute myocardiac infarction (heart attack) with accompanying increase in cardiac enzymes or troponins

Type II: Patient has history of coronary artery disease. There are two possible outcomes:

  • Coronary artery spasm with no appreciable increase in cardiac enzymes or troponins
  • Plaque erosion or rupture that evolves to acute myocardiac infarction (heart attack) with accompanying increase in cardiac enzymes or troponins

Type III: Patient has history of coronary artery disease and a drug eluting coronary stent. There are two possible outcomes:

  • Coronary artery spasm with no appreciable increase in cardiac enzymes or troponins
  • Thrombosis that evolves to acute myocardiac infarction (heart attack) with accompanying increase in cardiac enzymes or troponins

A number of mast cell mediators have effects that can cause coronary spasm or thrombosis.  Beyond their direct effects, they also perpetuate an inflammatory cycle that results in activation and infiltration by inflammatory cells

Mediator Effect
Histamine Coronary vasoconstriction, activation of platelets, increase expression of tissue factor
Chymase Activation of interstitial collagenase, gelatinase, stromelysin resulting in plaque rupture, generation of angiotensin II, a powerful vasoconstrictor
Cathepsin D Generation of angiotensin II, a powerful vasoconstrictor
Leukotrienes (LTC4, LTD4, LTE4) Powerful vasoconstrictor, levels increased during acute unstable angina
Tryptase Activation of interstitial collagenase, gelatinase, stromelysin resulting in plaque rupture
Thromboxane Platelet aggregation, vasoconstriction
PAF Vasoconstriction, aggregation of platelets
Platelets Vasoconstriction, thrombosis



Kounis Syndrome (allergic angina and allergic myocardial infarction). Kounis NG, et al. In: Angina Pectoris: Etiology, Pathogenesis and Treatment 2008.

Lippi G, et al. Cardiac troponin I is increased in patients admitted to the emergency department with severe allergic reactions. A case-control study. International Journal of Cardiology 2015, 194: 68-69.

Kounis NG, et al. The heart and coronary arteries as primary target in severe allergic reactions: Cardiac troponins and the Kounis hypersensitivity-associated acute coronary syndrome. International Journal of Cardiology 2015, 198: 83-84.

Fassio F, et al. Kounis syndrome: a concise review with focus on management. European Journal of Internal Medicine 2016; 30:7-10.

Kounis Syndrome: Aspects on pathophysiology and management. European Journal of Internal Medicine 2016.

Symptoms, mediators and mechanisms: A general review (Part 2 of 2)


Gynecologic symptoms    
Symptom Mediators Mechanism
Irregular and painful menstruation Histamine (H1), bradykinin Smooth muscle constriction
Uterine contractions Histamine (H1), serotonin, bradykinin Smooth muscle constriction

Increased estrogen



Neurologic symptoms    
Symptom Mediators Mechanism
Appetite dysregulation Histamine (H1), histamine (H3), leptin Dysfunctional release of neurotransmitters, suppression of ghrelin
Disorder of movements Histamine (H2), histamine (H3) Dysfunctional release of neurotransmitters, increases excitability of cholinergic neurons
Memory loss Histamine (H1), histamine (H3) Dysfunctional release of neurotransmitters
Headache Histamine (H1), histamine (H3), serotonin (low) Dysfunctional release of neurotransmitters


Low serotonin


Decreased blood flow to brain

Depression Serotonin (low), TNF, histamine (H1) Low serotonin

Disordered release of dopamine

Irregular sleep/wake cycle Histamine (H1), histamine (H3), PGD2 Dysfunctional release of neurotransmitters
Brain fog Histamine (H3), inflammatory cytokines Dysfunctional release of neurotransmitters, neuroinflammation
Temperature dysregulation Histamine (H3) Dysfunctional release of neurotransmitters, dysfunctional release of catecholamines



Miscellaneous symptoms    
Symptom Mediators Mechanism
Bleeding diathesis (tendency to bleed easily) Tryptase, heparin Participation in anticoagulation pathways

IgE-independent anaphylaxis; or, I haven’t been this excited on a Tuesday night in a long time

Mast cell patients are intimately familiar with the phenomenon of testing positive for allergies to things you know aren’t problems and negative for things that almost killed you.  If you ask any health care provider what the allergy antibody is, they will say it is IgE.  And for the most part, that is true.  But mast cell patients suffer reactions that do not demonstrate an IgE pathway to their allergies and anaphylaxis, and it is reason most of us suffer for years before being diagnosed correctly.

The idea that anaphylaxis is a function directly executed by IgE is a deeply ingrained part of western medicine.  In this model, IgE specific for an allergen binds to the allergen, and binds to the IgE receptor on mast cells and basophils, resulting in massive degranulation.

This is the classic model of anaphylaxis, with some creative license:

  1. You come into contact with something. Let’s say it’s Peanut, an anthropomorphic peanut.
  2. Immune cells called B cells think they once saw Peanut in a dark alley behind a bar. Peanut could have been waiting for a ride like any responsible peanut who has been drinking, but dark alley = shady = Peanut is trouble.
  3. The B cells make “Wanted!” posters with a picture of the peanut on it. Many, many posters.
  4. The B cells make lots of IgE to make sure every cell in the body sees the Wanted! posters. There will be nowhere for peanuts to hide. (I swear that as I was typing, I just heard the theme to the Good, the Bad and the Ugly.  I SWEAR.)
  5. Everyone knows that Peanut is a bad guy. They have seen the poster many times.  They do not need to see it again.  Do not show the poster again.  WE KNOW PEANUT IS BAD, IGE.  GO HOME, IGE, YOU’RE DRUNK.
  6. You guys know what happens next.  Peanut shows up.
  7. Someone remembers that IgE has been coming around the bar with the poster of Peanut. Peanut = bad guy.
  8. Everyone is hoping that if they tell IgE where Peanut is that IgE will leave them alone. No one really likes IgE but he is making such a big deal about Peanut and maybe Peanut is bad.  A little bad.  No one really knows but they know they do NOT want to deal with IgE if Peanut gets away.
  9. IgE and Peanut have a Western style gun duel at high noon. IgE captures Peanut by binding to him.
  10. While IgE is bound to Peanut, he also binds to a mast cell, which is like home base. IgE knows that Peanut is trouble and he is part of a Peanut gang and they are all bad, too.
  11. Mast cells deploy the tanks, duckboats, submarines, helicopters and fighter planes in the early allergy response to fight the Peanut gang. This causes massive inflammation with effects throughout the whole body.  Mediators released in the early response include histamine and tryptase.
  12. Mast cells start building more defenses and release them a little at a time later on in the late allergy response. Mediators released in the late response include prostaglandins and leukotrienes.

But we all know that it doesn’t always happen like this, because mast cell patients often have normal tryptase and IgE despite having a massive anaphylactic event, or even normal histamine or prostaglandins.

Last month, a comprehensive paper described alternative anaphylaxis pathways in mice that may be analogous to what is happening to mast cell patients having anaphylaxis that is not mediated by IgE.  That is to say, this pathway needs more research to know for sure if it is what is happening to us, but I have been watching the literature on this closely for a while and I100% think this is real.

There have now been multiple reports of the ability to induce anaphylaxis in mice while interfering with the IgE allergy pathway (either by not making IgE or the IgE receptor, or by treating the mice with anti-IgE, which blocks the IgE from binding to the receptor). Scientists found that by anaphylaxis could be mediated by IgG if the trigger was given intravenously. In particular, they were able to identify the murine IgG2b as the antibody subclass responsible.  In mice, IgG2b can cause anaphylaxis when IgE is not able to participate, at all.

The most important mediator in IgE anaphylaxis is histamine.  But the most important mediator in IgG anaphylaxis is platelet activating factor (PAF).  PAF levels have been linked with severity of anaphylaxis previously (I wrote a post about this around this time last year).  This could explain why many patients have normal tryptase, n-methylhistamine or histamine levels despite a very short amount of time elapsed from anaphylaxis. This is not a histamine show.  And maybe the reason so many mast cell patients cannot get complete relief despite taking huge doses of antihistamines is because histamine isn’t the PRIMARY issue.  (Author’s note: Please do not stop taking your antihistamines.  I love my antihistamines.  Just saying I think maybe there is something happening above histamine in these reactions.)

It’s also not just a mast cell show.  IgG can activate basophils, monocytes and macrophages, and neutrophils to release PAF.  Human neutrophils can mediate IgG dependent anaphylaxis when infused into mice.  So now we have a mechanism for anaphylaxis that is not IgE independent – it can also be mast cell independent.  Mind blowing. (Worth mentioning here that the phenomenon of mast cell independent anaphylaxis is not new or specific to IgG anaphylaxis – groups have found instances of mast cell independent anaphylaxis for almost thirty years.)

PAF levels are much higher in anaphylaxis patients than in control patients, and the enzyme that degrades PAF, called PAF acetylhydrolase, is much lower. It is important to note that binding at the IgE receptor can also produce PAF, but that also causes degranulation and release of histamine and tryptase, which seems to be absent in some patients.

To induce IgG mediated anaphylaxis, you need more allergen than for IgE anaphylaxis.  A lot more. 100-1000x more.  So in mice that have both IgE and IgG for peanut (not really peanut), doesn’t it seem like the IgE would react first to the peanut, and you would have IgE anaphylaxis?  But that’s not what happens.  What happens is that the IgG scoops up the peanut faster than the IgE can.  The IgG can block IgE anaphylaxis.  (WHAT UP MAST CELL PATIENTS DOING WAY BETTER ON IVIG?!?!)

IgG anaphylaxis in mice has been exclusively isolated to triggers administered intravenously.  The reason this fact matters is because of the frequency with which people (who don’t always have mast cell disease) have anaphylaxis to intravenous antibody treats, like IVIG, monoclonal antibodies for treating various diseases, or transfusions (which contain IgG antibodies). Treatments of this kind provide a huge influx of allergen. This pathway favors IgG anaphylaxis over IgE anaphylaxis because of how the IgG will scoop the allergen up (see previous paragraph).

As a final aside, there is also the curious fact that a group of patients with CVID (common variable immunodeficiency, a primary immunodeficiency disease) have a mutation that makes one of the IgG receptors found on cells like mast cells WAY more active.  The CVID patients with this mutation also have antibodies to IgA and experience anaphylaxis after IVIG.

I know I have gone on and on but this is the most exciting thing to happen to tryptase and histamine normal anaphylaxis patients in the last decade, at least.  There is SO much work that needs to be done.  Mouse and human mast cells are different.  Mouse and human IgG antibodies are different.  They could not induce food allergy in mice with an IgG dependent mechanism.  We need to pursue research on the role of PAF specifically in anaphylaxis patients with normal tryptase and histamine.

But now, when you tell your doctor that anaphylaxis is not always IgE dependent, you can give them a reference to a solid paper that fairly describes the findings, the caveats and the strengths of the current research on IgE independent anaphylaxis.  And it’s not just speculation. PEOPLE OUTSIDE OF MAST CELL DISEASE RESEARCH GROUPS ACKNOWLEDGE THAT THIS IS REAL.  IGE INDEPENDENT ANAPHYLAXIS IS REAL.


Someone hold my Epipens while I make my dog dance with me.


Finkelman FD, Khodoun MV, Strait R. Human IgE-independent systemic anaphylaxis. J Allergy Clin Immunol 2016.


Cardiovascular manifestations of mast cell disease: Part 4 of 5

Heart failure is uncommon in mast cell patients, but is noteworthy as a condition that involves mast cell activation.  One study of adults with SM found 12 patients out of 548 had congestive heart failure.  A small study with 18 MCAS patients found that persistent mast cell activation did not affect such parameters as systolic left ventricular function, systolic and diastolic left ventricular diameter, or shortening fraction.  These markers are often tied to heart failure. In that same study, 12/18 MCAS patients did exhibit a diastolic left ventricular dysfunction.  This defect is a sensitive indicator of changes to the myocardium, muscle around the heart and can be found using Doppler imaging. Five of those MCAS patients also showed hypertrophy in the left ventricle, a thickening of tissue that can be linked to heart damage.

Importantly, these findings were not linked to chronic heart failure in this population.  Mast cell patients should be aware that while these anatomical changes of the left ventricle may be present, there is not currently any indication that their increase the frequency of symptomatic heart failure in this population.  Mast cells are heavily involved in tissue remodeling and it is possible that local mast cell activation can lead to laying of additional tissue or scarring.  Tryptase, chymase and matrix metalloproteinases, all released by mast cells, participate in tissue remodeling and fibrosis.

Tryptase has been associated with both heart failure and atherosclerosis, involved in coronary disease and syndromes.  A number of other mediators can also contribute to heart failure, including histamine, platelet activating factor, IL-4, IL-6, IL-10, TNF, fibroblast growth factor (FGF) and transforming growth factor beta (TGFB).

Treatment of heart failure in mast cell patients is not terribly different from that of the general population.  Diuretics are often used first, including furosemide. Angiotensin receptor antagonists like losartan are good choices for mast cell patients since ACE inhibitors and beta blockers should be avoided wherever possible.  Calcium channel blockers like verapamil can be used. Spironolactone or similar medications may provide additional benefit. Ivabradine, a newer medication that works by affecting the funny current (Author’s note: Not a joke!  My favorite pathway name), is also a consideration.  Digoxin is appropriate for atrial fibrillation (afib) where other attempts to correct rhythm have failed.


Kolck UW, et al. Cardiovascular symptoms in patients with systemic mast cell activation disease. Translation Research 2016; x:1-10.

Gonzalez-de-Olano D, et al. Mast cell-related disorders presenting with Kounis Syndrome. International Journal of Cardiology 2012: 161(1): 56-58.

Kennedy S, et al. Mast cells and vascular diseases. Pharmacology & Therapeutics 2013; 138: 53-65.

Cardiovascular manifestations of mast cell disease: Part 3 of 5

Recurrent or perpetual elevation in blood pressure has been observed in multiple studies and may affect up to 31% of patients with mast cell activation disease (systemic mastocytosis, mast cell activation syndrome/disorder, monoclonal mast cell activation syndrome). Despite this high prevalence, many providers continue to believe that this symptom cannot be inherently from mast cell activation.

A number of mast cell mediators are vasoconstrictors, narrowing the blood vessels and elevating blood pressure. Histamine can both increase and lower blood pressure depending on which receptor it acts upon (H1: hypotension; H2: hypertension).

Several mediators participate in the angiotensin-renin pathway. Angiotensin II, the level of which is largely determined by mast cell mediators like renin, strongly elevates blood pressure. Chymase, involved in the angiotensin-renin pathway, can also either increase or lower blood pressure depending on concentration relative to other mediators present. Carboxypeptidase A can also affect angiotensin II level as well. Renin regulates the level of a molecule that becomes angiotensin II and can increase blood pressure this way.

Phospholipases, which help produce the molecule needed to make prostaglandins, leukotrienes and thromboxanes can contribute to either high or low blood pressure depending upon which molecule is made. Prostaglandin D2 (PGD2) is a vasodilator, lowering blood pressure; but its metabolite, 9a,11b-PGF2, increases blood pressure. (Author’s note: I personally believe this to be the reason for the rapid blood pressure fluctuations in mast cell patients, but do not have evidence to directly support this.) Thromboxane A2, a molecule related to prostaglandins and leukotrienes, increases blood pressure, as do leukotrienes.

Management of high blood pressure is complicated in mast cell patients by the interaction of common antihypertensives with mast cell activation. Beta blockers are contraindicated in mast cell patients because they interfere with epinephrine, both naturally produced and medicinally.  Use of beta blockers is a risk factor for fatal anaphylaxis.  Any patient on beta blockers that carries an epipen should also carry a glucagon pen, which can be administered prior to the epipen to increase efficacy.

ACE inhibitors interfere with angiotensin converting enzyme, which increases blood pressure through the angiotensin II pathway.  ACE inhibitors affect bradykinin levels, a mast cell mediator that is also mast cell activating.  For this reason, ACE inhibitors can increase mast cell reactivity and symptoms like angioedema.

Author’s note:  I extended this series to four posts to discuss heart failure in mast cell patients.  Following this series, I will be posting a series dedicated exclusively to Kounis Syndrome, including diagnosis and treatment.  Sit tight!


Kolck UW, et al. Cardiovascular symptoms in patients with systemic mast cell activation disease. Translation Research 2016; x:1-10.

Gonzalez-de-Olano D, et al. Mast cell-related disorders presenting with Kounis Syndrome. International Journal of Cardiology 2012: 161(1): 56-58.

Kennedy S, et al. Mast cells and vascular diseases. Pharmacology & Therapeutics 2013; 138: 53-65.