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The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 28

36. Is MCAS less serious than SM?


There is a lot of literature presenting data on SM. There is a lot less on MCAS. This is largely because of how recently it has described and the fact that different sets of criteria make it impossible to do large scale studies as have been done with SM. So it’s hard to objectively compare the data because the same volume just doesn’t exist yet.

Many providers and researchers think of MCAS as a form of “preclinical SM”. This term was tossed around in the early 2000s by SM researchers who found patients that seemed to have SM but didn’t meet the criteria for it. There were a few presentations in which an image was shown of a line with the different types of SM shown.

From left to right, the line read:
Preclinical SM/Indolent SM/Smoldering SM/Aggressive SM/Mast cell leukemia

Based upon this figure, and the fact that we are trained to look at lines like this as continuum that either increases or decreases in order, many people latched onto “preclinical SM” (like MCAS) as being the least dangerous. Importantly, the figure refers to the increasing danger of permanent organ damage by mast cells ending up in organ tissues. It does NOT refer to the danger of anaphylaxis.

Indolent systemic mastocytosis (ISM) is the least dangerous form of SM and by far the most common. When people ask if MCAS is less dangerous than SM, they usually mean is MCAS less dangerous than ISM. A couple of small study groups have found that prevalence of anaphylaxis in MCAS is less frequent than in ISM. However, this comparison is flawed. Many people have known they have SM for 20+ years. MCAS hasn’t even been a viable diagnosis for 10 years. MCAS is also less likely to be diagnosed due to decreased exposure on the part of many providers. Many MCAS patients are diagnosed with idiopathic anaphylaxis instead so you’re not really looking at a robust population of MCAS patients in these studies.

ISM has a normal lifespan. It is treated the same way as MCAS and the two conditions have remarkably few differences beyond very specific markers that show the body making too many sloppy mast cells.

Some MCAS patients have protracted anaphylaxis and a normal baseline of very serious daily symptoms. It is my personal opinion that the anaphylaxis episodes I have observed in many MCAS patients can be a lot worse than you see in ISM. MCAS patients also have a harder time finding treatment. While ISM patients certainly run into unknowledgeable providers, it is my experience that having an ISM diagnosis is more helpful for facilitating treatment than an MCAS diagnosis.

We need time in order for larger studies and more unifying MCAS criteria to emerge but I am certain that these will follow. MCAS is at least as dangerous as ISM, if not more. Both MCAS and ISM are less dangerous than SSM, ASM and MCL.

For more detailed reading, please visit these posts:
The Provider Primer Series: Mast cell activation syndrome (MCAS)
The Provider Primer Series: Diagnosis and natural history of systemic mastocytosis (ISM, SSM, ASM)

The Provider Primer Series: Mast cell activation syndrome (MCAS)

Mast cell activation syndrome (MCAS), also called mast cell activation disorder (MCAD), is an immunologic condition in which mast cells are aberrantly activated, resulting in inappropriate mediator release.


  • MCAS can be responsible for chronic symptoms in multiple organs that cannot be attributed to another cause[vi].
  • Patients frequently receive diagnosis for a number of idiopathic conditions prior to correct diagnosis with MCAS[vi].
  • Mast cell activation syndrome is overwhelmingly a secondary condition. MCAS can be secondary to a number of conditions, including autoimmune diseases, connective tissue diseases, and atopic conditions[i].
  • The term “primary MCAS” refers to mediator release symptoms associated with mastocytosis[xvii] . However, the term “mastocytosis” generally conveys the understanding that both proliferation and mediator release symptoms are possible.
  • In idiopathic MCAS, no cause for symptoms can be identified[xvii] .
  • The presence of multiple mast cell patients in one family is not uncommon. A heritable gene has not yet been identified. Epigenetic mechanisms are suspected for transmission of mast cell disease to another generation[iv].
  • Approximately 75% of mast cell patients have at least one first degree relative with mast cell disease and not always the same subtype[ii]. For example, a mother may have MCAS, while one of her children has SM and the other has CM.

Diagnostic criteria

  • MCAS is a recently described diagnosis. In the absence of large studies, several groups have developed their own, sometimes conflicting, diagnostic criteria.
  • Differential diagnoses with potential to cause similar symptoms should be considered and excluded[iii].
  • The criteria most frequently used include those by a 2010 paper by Akin, Valent and Metcalfe[iii]; a 2011 paper by Molderings, Afrin and colleagues[iv]; and a 2013 paper by Castells and colleagues[v].
  • The criteria described in the 2011 paper by Molderings, Afrin and colleagues have been updated to include response to medication[vi].
  • Of note, a 2012 consensus proposal[x] was authored by a number of mast cell experts including Valent, Escribano, Castells, Akin and Metcalfe. It sees little practical use and is not generally accepted in the community.
  • The major sets of criteria listed above all include the following features:
    • Recurrent or chronic symptoms of mast cell activation
    • Objective evidence of excessive mast cell mediator release
    • Positive response to medications that inhibit action of mast cell mediators
  • Valent warns that in some cases, patients may not fulfill all criteria but still warrant treatment: “In many cases, only two or even one of these three criteria can be documented. In the case of typical symptoms, the provisional diagnosis of ‘possibly MCA/MCAS’ can be established, and in acute cases, immediate treatment should be introduced.”[vii]

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[viii].
  • Serum tryptase and 24 hour urine testing for n-methylhistamine, prostaglandin D2, prostaglandin 9a,11b-F2 are frequently included in testing guidelines in literature (Castells 2013)[ix], (Akin 2010)[x], (Valent 2012)[xi].
  • It can be helpful to test for other mast cell mediators including 24 hour urine testing for leukotriene E4[xii]; plasma heparin[xiii]; and serum chromogranin A[xiv].
  • In most instances, elevation of a mediator must be present on two occasions[ix]. This helps to exclude situations of appropriate mast cell activation, such as infection or wound healing.
  • For patients with baseline tryptase level >15 ng/mL, elevation of tryptase above this baseline is only required on one occasion[viii].

Symptoms associated with mast cell activation

  • Mediator release causes a wide array of symptoms, including hypertension[xv], hypotension, hypertension, wheezing, itching, flushing, tachycardia, nausea, vomiting, diarrhea, constipation, headache, angioedema, fatigue, and neurologic symptoms[iv].
  • In a small MCAS cohort (18 patients), 17% had a history of anaphylaxis[xvii] . A larger data set is desirable.
  • Patients with history of anaphylaxis should be prescribed epinephrine autoinjectors[v]. If patient must be on a beta blocker, they should be prescribed a glucagon injector for use in the event of anaphylaxis[v].

Response to medications that inhibit action of mast cell mediators

  • Treatment of MCAS is complex and may require a number of medications. Second generation H1 antihistamines; H2 antihistamines; and mast cell stabilizers are mainstays of treatment[xvi].
  • Additional options include aspirin; anti-IgE; leukotriene blocker; and corticosteroids[xiii] .
  • First generation H1 antihistamines may be used for breakthrough symptoms[xiii] .
  • “An important point is that many different mediators may be involved in MCA-related symptoms so that the final conclusion the patient is not responding to antimediator therapy should only be drawn after having applied several different antimediator-type drugs[xiii] .
  • Inactive ingredients are often to blame for reaction to mast cell mediator focused medications. Many mast cell patients see benefit from having medications compounded[xvii].

Natural history

  • In one MCAS cohort of 18 patients, 33% had a complete (no unmanaged symptoms) response and 33% had a major (only one serious symptom) response after one year of mast cell treatment[xviii].
  • In another MCAS cohort of 135 patients, 51% demonstrated significant improvement, 11% had no obvious change in symptom severity and 38% experienced worsening symptoms[v]. (Author’s note: While described in an Afrin 2016[v] paper, the data from this cohort has not yet been published. Molderings is the principle investigator.



[i] Frieri M, et al. (2013). Mast cell activation syndrome: a review. Current Allergy and Asthma Reports, 13(1), 27-32.

[ii] Molderings GJ, et al. (2013). Familial occurrence of systemic mast cell activation disease. PLoS One, 8, e76241-24098785

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

[iv] 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

[v] Castells M, et al. (2013). Expanding spectrum of mast cell activation disorders: monoclonal and idiopathic mast cell activation syndromes. Clin Ther, 35(5), 548-562.

[vi] Afrin LB, et al. (2016). Often seen, rarely recognized: mast cell activation disease – a guide to diagnosis and therapeutic options. Annals of Medicine, 48(3).

[vii] Valent P. (2013). Mast cell activation syndromes: definition and classification. European Journal of Allergy and Clinical Immunology, 68(4), 417-424.

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

[ix] 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.

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

[xi] 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.

[xii] 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.

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

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

[xv] Shibao C, et al. (2005). Hyperadrenergic postural tachycardia syndrome in mast cell activation disorders. Hypertension, 45(3), 385-390.

[xvi] Cardet JC, et al. (2013). Immunology and clinical manifestations of non-clonal mast cell activation syndrome. Curr Allergy Asthma Rep, 13(1), 10-18.

[xvii] Afrin LB. “Presentation, diagnosis and management of mast cell activation syndrome.” In: Mast Cells. Edited by David B. Murray, Nova cience Publishers, Inc., 2013, 155-232.

[xviii] Hamilton MJ, et al. (2011). Mast cell activation syndrome: a newly recognized disorder with systemic clinical manifestations. Journal of Allergy and Clinical Immunology, 128(1), 147-152.e2

Initial diagnosis and treatment of mast cell activation disease: General notes for guidance

Mast cell disease is becoming more well known among both the public and medical providers, but there is still a lot of confusion regarding exactly what it is, how to diagnose and how to treat.

There are several tests that should be used when working up a patient for mast cell disease. Tryptase is the most well known of these tests, due to over 85% of patients with systemic mastocytosis (SM), a form of mast cell disease, having elevated tryptase. However, tryptase can be normal in mast cell patients, or may only be elevated during times of severe symptoms or anaphylaxis. While an elevated baseline tryptase can be used as confirmation for a mast cell disease (in the absence of frank hematologic disease), a normal tryptase test should not be used to discard the possibility of mast cell disease.

24-hour urine tests for mast cell mediators are most likely to capture evidence of mast cell activation when executed correctly. These tests measure n-methylhistamine, a metabolite of histamine, and prostaglandins D2 and F2a, which are all released by mast cells. Urine collected for this test should be kept refrigerated or on ice during collection and transport to the lab. I STRONGLY recommend communicating with the lab prior to beginning to this test to be sure that they understand the temperature requirements. The molecules being tested are not stable at room temperature and inappropriate storage can result in a negative test result in a positive patient. (For details on this topic and specific recommendations for testing, please refer to Afrin 2013).

Some providers also find utility in the measurement of other less specific mediators. Please refer to my previous post on this topic:

Due to the well established time sensitive nature of these tests (Afrin 2013), a patient who presents a “mast cell clinical picture” and responds to typical mast cell medications may in fact have mast cell disease in the presence of negative tests.

Depending on the clinical picture, a provider may feel it necessary to order a bone marrow biopsy, skin biopsy or biopsy of another organ to determine if mast cell infiltrates are present. This is not always immediately done in the presence of positive tryptase, n-methylhistamine, D2 prostaglandin or F2a prostaglandin test and will not always affect treatment. It is common knowledge among mast cell fluent providers that a negative biopsy does not exclude mast cell disease, but it is instead used to rule in the presence of specific proliferative entities like systemic mastocytosis (Picard 2013, Molderings 2011). Furthermore, a single biopsy may fail to capture a positive specimen in a known-positive patient (Butterfield 2004).

For more specific details regarding differentiation among the diagnostic categories of mast cell disease, please refer to my previous post on this topic:

There are a number of well known, well tolerated medications that can be used to manage mast cell disease. First line medications include antihistamines, leukotriene inhibitors, and mast cell stabilizers (Cardet 2013, Picard 2013, Molderings 2011, Afrin 2013).

Histamine is released by activated mast cells in large quantities. Histamine acts on the body by interacting with four different types of receptors, called H1, H2, H3 and H4. Medications that block the H1 and H2 receptors are available in plentiful supply in many countries. Once diagnosed, mast cell patients generally begin daily treatment with both H1 and H2 antihistamines. Longer acting, non-sedating H1 blockers like cetirizine are typically used to provide a baseline H1 coverage. H2 coverage is achieved with medications like Zantac or Pepcid. Dosage can be increased as needed to provide effective symptom relief, and these medications are often taken in moderate to high doses by mast cell patients. It is not uncommon to take multiple drugs together to block one type of histamine receptor, but this should be managed by a provider.

Leukotrienes are also released by activated mast cells. Singulair is an example of a leukotriene inhibitor that is a common add-on for mast cell patients. This medication is not a replacement for antihistamines.

Mast cell stabilizers achieve effects by making mast cells less likely to release chemicals. Cromolyn is typically the first line mast cell stabilizer in the US. This medication can take several weeks to demonstrate its full effect, so patients and providers should be aware of this fact. Another mast cell stabilizer, ketotifen, is also available in the US through compounding pharmacies. Ketotifen is also an H1 antihistamine.

Medications should ideally be added one at a time to allow easy identification of a bad actor in the event of a med reaction. As a result, tweaking a patient’s medication regimen takes time and patience. If a patient reacts to a medication, care should be taken to determine if the medication is truly the issue or if it is an inactive ingredient in the preparation (lactose, etc).

Mast cell disease can result in a highly variable clinical picture and mast cell patients are often only diagnosed following years of investigation for other possible causes of their symptoms. For this reason, many mast cell patients have acquired a long list of diagnoses prior to a mast cell diagnosis. In some cases, these diagnoses may be accurate and co-existing. All existing prior diagnoses should be considered for their accuracy in light of a mast cell diagnosis.

Additionally, there are a number of conditions which are frequently comorbid with mast cell disease, including Ehlers Danlos syndrome, postural orthostatic tachycardia syndrome (POTS), a variety of autoimmune diseases and several digestive conditions.  Patients should be evaluated according to their clinical picture and laboratory findings.



Afrin, Lawrence B. Presentation, Diagnosis and Management of Mast Cell Activation Syndrome. 2013. Mast Cells.

Juan-Carlos Cardet, Maria C. Castells, and Matthew J. Hamilton. Immunology and Clinical Manifestations of Non-Clonal Mast Cell Activation Syndrome. Curr Allergy Asthma Rep. Feb 2013; 13(1): 10–18.

Matthieu Picard, Pedro Giavina-Bianchi, Veronica Mezzano, Mariana Castells. Expanding Spectrum of Mast Cell Activation Disorders: Monoclonal and Idiopathic Mast Cell Activation Syndromes. Clinical Therapeutics, Volume 35, Issue 5, May 2013, Pages 548–562.

Gerhard J Molderings, Stefan Brettner, Jürgen Homann, Lawrence B Afrin. Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. Journal of Hematology & Oncology 2011, 4:10.

MCAS: Neurologic and psychiatric symptoms

The neuropsychiatric symptoms associated with MCAS are numerous and are results of the chemicals released by mast cells.

Headaches are a very common complaint. They can sometimes be managed with typical remedies (Excedrin, Tylenol) and antihistamine treatment often helps with this symptom quickly. However, in some patients, headaches can be disabling. Diagnosis of migraine is not unusual, with mast cell degranulation having been tied previously to migraines.

Dizziness, lightheadedness, weakness, vertigo, and the feeling of being about to faint are all typical in MCAS, though true fainting spells are less common than in mastocytosis. These symptoms often cause many MCAS patients to be diagnosed with dysautonomia or POTS.

MCAS patients often experience increased activation of sensory and motor nerves. This manifests as generic neurologic symptoms, sometimes several at once, like tingling, numbness, paresthesia and tics. Tics generally do not spread from the place they initially present. Paresthesias seem to progress for a period of time, then wane and disappear. Extremities are most commonly affected.

EMG and nerve conduction studies are typically normal or abnormal in a way that is not diagnostic. These tests sometimes reflect a possibility of chronic inflammatory demyelinating polyneuropathy (CIDP.) These patients also sometimes are positive for monoclonal gammopathy of unknown significance (MGUS), a blood marker that has been tied to multiple myeloma. However, in these patients, the MGUS is believed to be an effect of the MCAS.

Another subset of patients are diagnosed with subacute combined degeneration (SCD), a deterioration of the spinal cord associated with B12 deficiency. They are sometimes treated for pernicious anemia despite lack of hematologic support for this diagnosis.

Prostaglandin D2 is a known effector of nerve damage and has been blamed for many of the neurologic symptoms seen in MCAS. Astrogliosis, abnormal proliferation of astrocytes (nerve cells in the brain), and demyelination (loss of the insulating cover for nerves that allows the body to send signals) are markers of neurodegeneration. These factors cause scarring and inhibit nerve repair mechanisms. PGD2 is made by an enzyme called hematopoietic PGD synthase. In mice that don’t make this enzyme, these kinds of neuroinflammation are suppressed. Treatment of normal mice with an inhibitor of this enzyme (HQL-72) also decreases these actions. This indicates that PGD2 is critical in causing neuroinflammation including demyelination. PGD2 also activates pain receptors strongly, causing sometimes profound neurologic pain.

PGD2 is also the most potent somnagen known, meaning that it induces sleep more strongly than any other molecule. MCAS patients report inordinately deep sleep, “mast cell coma.” This is likely due to excessive PGD2. Conversely, some MCAS patients also have insomnia, from excessive histamine.

I have written at length before about cognitive and psychiatric manifestations of mastocytosis, which are the same as in MCAS. Cognitive and mood disturbances are all kinds are reported. Brain fog, including short term memory troubles and word finding problems, is the most common symptom. Irritability, anger, depression, bipolar affective disorder, ADD, anxiety, panic disorders and even sometimes frank psychosis can present. Such symptoms in mastocytosis patients were referred to as mixed organic brain syndrome, a term coined in 1986. The important aspect of these symptoms in MCAS is that they are caused by mast cell activation. As such, they are most effectively treated by managing mast cell release symptoms. Some patients do find relief in some psychiatric medications, but the psychiatrist should be aware that these symptoms are part of mast cell pathology.

Additionally, PTSD is not rare in MCAS patients. This is most often due to the trauma from negative interactions with the medical industry.

Autism is significantly increased in patients with mastocytosis. Similar findings are beginning to surface with MCAS patients. Interesting, most autism spectrum disorder patients have food intolerance and general allergic symptoms. A future post will discuss this in more detail.


Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome. 2013. Mast cells.

Molderings GJ, Brettner S, Homann J, Afrin LB. Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. J. Hematol. Oncol.2011;4:10-17.

Ikuko Mohri, Masako Taniike, Hidetoshi Taniguchi, Takahisa Kanekiyo, Kosuke Aritake, Takashi Inui, Noriko Fukumoto, Naomi Eguchi, Atsuko Kushi, Hitoshi. Prostaglandin D2-Mediated Microglia/Astrocyte Interaction Enhances Astrogliosis and Demyelination in twitcher. The Journal of Neuroscience, April 19, 2006 • 26(16):4383– 4393.

Rogers MP, et al. Mixed organic brain syndrome as a manifestation of systemic mastocytosis. Psychosom Med. 1986 Jul-Aug;48(6):437-47.


MCAS: Kidney, urinary and genital concerns

Like so many other places in the body, the genitourinary tract of MCAS patients can easily become inflamed.  Many patients, especially women, are treated for chronic urinary tract infections despite negative cultures.  Male MCAS patients are often diagnosed with prostatitis.   Vaginal inflammation, painful inflammation, and vulvodynia/ vulvar vestibulitis are also found frequently in mast cell patients.  (Please see previous post on vaginal pain in chronic disease.)
Mast cells are not often found in healthy renal tissue, but they are frequently present in various types of renal disease.  They are most commonly associated with tubulointerstitial nephritis associated with fibrosis and renal failure, including glomerulonephritis, diabetic nephropathy, allograft rejection, amyloid disease, polycystic kidney disease, reflux nephropathy and others.  Mast cells drive fibrosis and their presence correlates with decrease in glomerular filtration and a poor prognosis. 
MCAS patients with urinary pain often suffer from obstructive ureteral angioedema, swelling of the urethra that prevents the urine from passing through it.  Persistent lower back pain is common, with flank pain and lower abdominal quadrant pain being less common.
Fertility issues are not rare in mast cell patients.  Luteinizing hormone activates mast cells, which release histamine to stimulate ovarian contractility, ovulation and progesterone release by follicles.  Histamine is necessary for these functions and antihistamines can prevent ovulation.  Frequent miscarriage should not be readily attributed to mast cell disease.  Antiphospholipid antibodies should be considered. 
Mast cell degranulation has been implicated in testicular sclerosis via production of 15d-prostaglandin J2.  Mast cell stabilizers can help treat oligospermia significantly enough to result in pregnancy.  Decreased libido and erectile dysfunction is common in mast cell disease, including MCAS.
15-20% of women in childbearing years have endometriosis.  Endometriosis is the occurrence of endometrial tissue outside of its normal location.  In these patients, endometrial tissue is often found in the peritoneum.  These ectopic tissues are often fibrosis and cause significant inflammation. 
Mast cells are significantly increased in endometrial lesions, with 89% showing significant activation in regions that stain heavily for CRH and urocortin.  Mast cells in normal and proliferative endometrium are not activated.  Additionally, IL-1a, IL-6 and TNFa, among other inflammatory mast cell mediators, are increased in the tissue and fluids surrounding endometrial lesions.  (A detailed post on this is coming soon.)
Interstitial cystitis is often misdiagnosed as endometriosis.  In IC, urinary urgency, increased urinary frequency, suprapubic and pelvic pain and pain on intercourse are the most common symptoms.  IC is caused by increased mast cells in the bladder.  In IC patients, 146 mast cells were found over 10 high power fields; in patients with bacterial bladder infections, 97 were found; and in health controls, 51 were found.  (A detailed post on this is also coming.)

Sant, Grannum R., Kempuraj , Duraisamy, Marchand , James E., Theoharides, Theoharis C.  The mast cell in interstitial cystitis: role in pathophysiology and pathogenesis.  2007.  Urology 69 (Suppl 4A): 34-40.
Holdsworth SR, Summers SA.  Role of mast cells in progressive renal disease.  J. Am. Soc. Nephrol. 2008 Dec; 19(12):2254-2261.
Kempuraj D, Theoharides TC, et al.  Increased numbers of activated mast cells in endometrial lesions positive for corticotropin-releasing hormone and urocortin.  Am. J. Reprod. Immunol. 2004; 52:267-275.
Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome.  2013.  Mast cells.

MCAS: Anemia and deficiencies

Anemia is the most common issue affecting red blood cells in MCAS patients.  It can be macrocytic (big cells), normocytic (normal size), or microcytic.  Usually mild to moderate, but occasionally the diagnosis is mistaken for pure red cell aplasia on bone marrow examination.  When macrocytosis is predominant, BMB must be performed to rule out myelodysplastic syndrome (MDS.) 
Cobalamin deficiency is common, even when pernicious anemia is ruled out.  Copper deficiency is sometimes the cause for microcytic anemia, although in MCAS, it sometimes causes normocytic or macrocytic anemia.  This may be caused by absorption, but is also a side effect of overdose of zinc, a common ingredient in over the counter medications taken by MCAS patients to reduce symptoms. Folate deficiency is less frequently found in MCAS and is often due to hemolysis from an acquired condition like acquired chronic autoimmune hemolytic anemia, sometimes found to occur secondary to mast cell disease.  Other hemolytic conditions, like paroxysmal nocturnal hematouria, should be ruled out.
Many MCAS patients have selective iron malabsorption, which sometimes resolves with antihistamine treatment.  GI bleeds must be excluded.  Oral iron absorption tests can be done to test iron malabsorption.  A recent procedure calls for a blood sample to establish baseline plasma iron, administration of 100mg dose of oral sodium ferrous citrate, and another blood sample to test plasma iron two hours later.  Increase of less than 50 ug/dl is considered evidence of malabsorption.
Iron malabsorption can happen for several reasons in the context of MCAS.  Iron deficiency can be from MCAS immune dysfunction that leads to generation of antibodies against the acid secreting cells of the stomach.  When the concentration of stomach acid is too low (achlorhydria), the absorption of non heme dietary iron is dramatically reduced.   H2 antihistamines and PPI medications can interfere with iron absorpotion.   Hepcidin, the production of which is stimulated by mast cell mediators like IL-6 and TNFa, slows down the rate with which GI cells transfer the iron into the blood stream for use.
MCAS patients sometimes exhibit low serum iron and ferritin, but have normal MCV and RCDW, which indicates no deficiency is present.  This profile is thought to allude to correct transport of iron to the blood stream but poor utilization in the bone marrow. 

Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome.  2013.  Mast cells.
Kobune M, et al.  Establishment of a simple test for iron absorption from the gastrointestinal tract.  Int. J. hematol. 2011; 93:715-719.
Hitchinson C, et al. Proton pump inhibitors suppress absorption of dietary non-haem iron in hereditary hemochromatosis.  Gut 2007 Sep; 56(9):1291-1295.

MCAS: Blood, bone marrow and clotting

One of the reasons MCAS is so difficult to diagnose is because it often has no effect on routine blood work.  Mast cells leave the bone marrow early in their lives, circulate in the blood stream very briefly, and then live in peripheral tissues for life spans of several months to about three years.  The reason many MCAS patients have no obvious hematologic abnormalities is that mediator release in these peripheral tissues usually doesn’t affect generation of blood cells or the blood cells already circulating. 
Hematologic issues are more commonly found in proliferative disease, like SM.  Still, one study found that in SM patients, random bone marrow biopsies missed the diagnosis 1/6 of the time.  For patients in whom SM is suspected, a second BMB can be helpful and bilateral biopsies are being ordered more frequently. 
MCAS patients very rarely have increased numbers of mast cells, spindled cells, CD2/25 receptor expression or the CKIT D816V mutation.  On examination of marrow, when irregularities are found, they are off a mild “myeloproliferative/myelodysplastic” nature, which sometimes leads to a diagnosis of MDS.  These patients do not respond to MDS treatments.
When serum tryptase is less than twice the upper limit of normal, BMB is not recommended due to how infrequently abnormalities are found.  Even during reactions, MCAS patients usually have normal tryptase values.  In recent years, a tryptase of 20% + 2 ng/ml above baseline has become regarded as evidence of activation, but this is not universally accepted.
MCAS patients often have normal blood counts, white blood cell differentials and bone marrow findings.  But there is now a growing population of MCAS patients with evident abnormalities.  Elevation of monocytes is the most common irregularity, followed by elevation of eosinophils, and then elevation of basophils.  High reactive lymphocytes are often identified in these patients on manual differential.  White blood counts can be high or low, often for no clear reason, and usually mild, but sometimes severe.  Likewise, platelets can be high or low, which sometimes garners patients a diagnosis of essential thrombocytosis or immune thrombocytopenia. 
Overproduction of red blood cells can occur to excessive release by mast cells or other cells of mediators stimulating production.  Sometimes patients are originally diagnosed with and treated for polycythemia vera, but do not improve. 
Poor clotting and easy bruising is found in a lot of MCAS patients due to activation that releases heparin.  By itself, it does not typically require treatment.  The bleeding is often localized, such as excessive bleeding from a surgical site but clotting correctly elsewhere.  Antihistamines typically help, with protamine being reserved for severe cases and transexamic acid and aminocaproic acid being reserved for the most severe.
Thromboembolism, formation of a clot in one vessel that breaks away and impedes blood flow in another vessel, is not rare in MCAS patients, even those with normal coagulation labs.  Some patients have low or high PT or PTT values.  Antiphospholipid syndrome should be excluded. 
Heparin released by mast cells activates anti-thrombin III and factor XII, which activate the rest of the intrinsic clotting cascade.  Heparin also stimulates the formation of bradykinin, which in turn causes vascular dilation and loss of fluid volume from the vessels into the tissues.  This is notable as a non-histamine route that can cause angioedema, low blood pressure and fainting in MCAS patients.

Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome.  2013.  Mast cells.
Sur R. Cavender D. Malaviya R. Different approaches to study mast cell functions. Int. Immunopharmacol. 2007 May; 7(5):555-567.
Butterfield JH, Li C-Y. Bone marrow biopsies for the diagnosis of systemic mastocytosis: is one biopsy sufficient? Am. J. Clin. Pathol. 2004; 121:264-267.

MCAS: Effects on eyes, ears, nose and mouth

MCAS patients suffer a variety of symptoms in systems localized to the head, often without well characterized explanations.  Eye, ear, sinus, nasal and mouth symptoms are often documented.
Generic irritation of the eyes, including dry eyes and/or itchy eyes, are the most common ophthalmologic complaint.  Excessive tearing is also common.  Like many other symptoms, the tearing can be occasional or chronic.  Redness, irritation of the sclera (the white part of the eye), the eye lid, and conjunctivitis can all affect one or both eyes.  Tremors and tics of the lid are sometimes found.  When particularly bothersome, patients sometimes seek treatment with botulinum toxin (Botox).  This treatment is at first successful, but the issue later resurfaces.
Difficulty in focusing in both eyes is particularly common when suffering other MCAS symptoms.  Despite seeking ophthalmologic explanations for these symptoms, most patients have no obvious cause of their inflammation.  32% of MCAS patients report eye issues. 
Symptoms affecting both anatomy and function of the ears are not atypical.  Irritation of the outer ear is unusual, but middle ear irritation, resembling an infection, is extremely common.  These “infections” often occur frequently and are resistant to antibiotic treatment because they are, in fact, the result of sterile inflammation. 
Hearing abnormalities are often found in MCAS patients.  They include hearing loss, ringing of the ears, and sensitivity to sound.  This is thought to be from sclerosis of the innter ear bones or tympanic membrane, which has been known to occur coincidentally with mast cell disease since the 1960’s.  Deterioration of the canal hairs and auditory nerve is also suspected in some patients.  Tinnitus is likely from mediator release causing overstimulation of the hair cells and auditory nerve fibers.  The most common finding by audiologists is sensorineural hearing loss of unclear origin.
Mast cells are densely concentrated in the cavities and passages of sinuses and in the nose.  Congestion, inflammation, ulceration, sores and pain are all common.  MCAS patients often have a heightened sense of smell with systemic reactions possible from an offending scent.  Unprovoked nose bleeds sometimes occur, which is thought to be from increased local concentration of heparin.
Pain in the mouth and lips is a frequent complaint.  Like so many other MCAS symptoms, it can be focal or diffuse, mild or disabling.  It is often found with leukoplakia, but yeast infection is not found.  Distorted sense of taste, especially where things often taste of metal, is common.  Ulcerations and sores often present.  While on preliminary examination they resemble herpes sores, they almost never are in MCAS patients. 
MCAS is associated with burning mouth syndrome, which is exactly what it sounds like.  The mucosa is normal on biopsy.  Mast cell mediator therapy can relieve pain, sometimes very quickly. 
Evidence of angioedema is often seen in the mucosa of the cheeks, tongue and lips.  Patients often undergo evaluation for hereditary angioedema.  While they are sometimes found to have decreased levels of C1 esterase antigen or function, it is not low enough to account for the angioedema.  This finding is often a red herring. 
Dental decay, often despite excellent dental hygiene, is being reported with increasing frequency.  It can be a lifelong issue or sudden onset.   There are several reasons suggested for this, but none definitive. 

Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome.  2013.  Mast cells.

Mast cell mediators: Recommended testing for MCAS diagnosis

Lab tests specific to mast cell activation for suspected MCAS patients should include serum tryptase, serum chromogranin A, plasma histamine, chilled plasma PGD2, stat chilled plasma heparin, chilled urine for PGD2, PGF2a and n-methylhistamine. 
Tryptase is the most famous mast cell mediator.  It is a complex molecule with many functions in the body.  It is easily damaged by heat and has a short half-life in the body (6-8 minutes in health subjects, 1.5-2.3 hours in patients with hypersensitivity reactions.  In separated serum, it can last approximately four days.  Serum tryptase value is usually normal in MCAS patients, but sometimes it is elevated.  Tryptase values that show an increase of 20% + 2 ng/ml above the baseline level are considered diagnostic for MCAS.
Chromogranin A is a heat-stable mast cell mediator.  High levels can suggest MCAS, but other sources must first be ruled out, such as heart failure, renal insufficiency, neuroendocrine tumors and proton pump inhibitor (PPI) use.  Starting or stopping PPI therapy will generally cause a change in value within five days.  Once other causes have been excluded, serum chromogranin A can be considered a reliable marker of mast cell activity. 
Heparin is a very sensitive and specific marker of mast cell activation.  However, due to its quick metabolism in the body, it is very difficult to measure reliably.  It has a very short half life and quickly deteriorates, even when refrigerated.  Values above 0.02 anti-Factor Xa units/ml are abnormal, but many commercial tests cannot test that low.  Elevated plasma heparin is sometimes found in MCAS patients. 
Histamine is also released by basophils, but the majority is released by mast cells.  It is heat stable and has a short half life in the body.  Serum histamine peaks at about 5 minutes after release and returns to baseline within 15-30 minutes in most patients.  In separated plasma, it is stable at room temperature for at least 48 hours.  It is broken down to n-methylhistamine, which is more stable and can be measured accurately longer.  N-methylhistamine is usually measured in a 24 hour urine test to account for the variability in release over the course of the day. 
Prostaglandin D2 is produced by several other cell types, but mast cell release is responsible for the dominant amount found in the body.  MCAS patients typically produce much higher levels of PGD2 than n-methylhistamine.  PGD2 is less stable than histamine, being metabolized completely in an estimated 30 minutes.  Its metabolite, PGF2a, is the preferred compound for detection due to its superior stability.    Accurate prostaglandin testing relies upon refrigeration of the sample from the start of collection through testing.  NSAIDs inhibit prostaglandin production and can lower PGD2 in blood and urine.  Renal insufficiency may produce an inaccurately low test value, but elevated prostaglandins are sometime seen in patients with renal disease.  Prostaglandins D2 and F2a can be tested in serum, but 24 hour urine samples are considered more accurate.

Leukotriene B4 and cysteinyl leukotrienes C4, D4 and E4 have been noted to be elevated in SM patients and during acute asthma attacks.  Though commercial testing for these compounds is not easily accessible, but they may be elevated in MCAS patients as well.  Other less specific mast cell mediators that are sometimes abnormal in MCAS patients include Factor VIII, plasma free norepinephrine, tumor necrosis factor alpha, and interleukin-6.

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Cardiovascular symptoms of MCAS

MCAS patients often have a number of cardiovascular symptoms.  In true mast cell disease fashion, these symptoms often represent both ends of the spectrum.
Heart palpitations are the most common cardiac complaint, with true rhythmic abnormalities being fairly rare.  Tachycardia is also very common, but occasionally slow heart rate (bradycardia) is reported.  In bradycardic patients, no obvious cause for this can be identified.  Both low and high blood pressure can be seen, many times in the same patient, sometimes even following one after the other in a short period of time.  These changes in blood pressure often have no clear trigger.
True syncope (fainting) is uncommon in MCAS, but presyncope (lightheadedness, weakness, dizziness or vertigo) affects the majority of patients.  These presyncope episodes can be distinct from POTS symptoms, and may not be related to position.  Some patients experience as many as several episodes a day.  When tested for POTS with tilt table, MCAS patients may or may not be positive.  However, when treated for POTS, mast cell patients in general only see mild reduction in their presyncope episodes, with little improvement in their other symptoms.
MCAS patients often complain of chest pain, which may or may not reveal ECG abnormalities.  This type of pain is generally localized specifically to the chest and does not radiate down the arm.  Chest pain must be carefully evaluated due to the potential for two rare cardiac syndromes.  Additionally, mast cell disease can indirectly cause congestive heart failure by the long term action of histamine. 
Takotsubo syndrome, or stress-induced cardiomyopathy, is caused by sudden weakening of the myocardium that causes ballooning of the left ventricle.  It can cause acute heart failure, ventricular arrhythmias, and acute heart failure.  Angiography shows that there is no coronary artery defect to explain the left ventricular abnormalities.  If the patient survives, the left ventricle typically returns to normal after about eight weeks.  This does not occur as a result of an allergic reaction, but is sometimes seen in patients with idiopathic anaphylaxis.  In 75% of patients, serum catecholamines are elevated, a finding sometimes seen in MCAS patients.  Due to severe emotional stress frequently being the trigger for the cardiac event, Takotsubo syndrome is also known as broken heart syndrome.
Kounis syndrome is also known as allergic angina or allergic myocardial infarction.  In these patients, there are no obstructive lesions in the coronary artery.  Patients suffer severe chest pain or heart attack as an extension of an allergic reaction.  Kounis syndrome is caused by mast cell activation causing vasospasm of the coronary artery.  It is not known if the mast cells effecting this pathology are normally developed mast cells or improperly developed, such as seen in mastocytosis and MCAS.  This syndrome accounts for about 0.002% of all acute heart attacks.  (An in depth post on Kounis syndrome is on the way.)
MCAS patients often experience coronary and peripheral atherosclerosis.  Some have pain due to narrowing of the vessels.  Sclerosis and poor healing is seen in many MCAS patients.  Due to the importance of mast cells in angiogenesis, long term mast cell activation can contribute to aneurysms, hemorrhoids, varicosities, hemangiomas, arteriovenous malformations and telangiectasias. 
Edema is a common finding.  Most MCAS patients who have edema have no heart abnormalities and do not have pitting edema, indicating that the edema is likely not from heart disease.  MCAS patients often have widespread edema that can shift to different parts of the body.  There is usually no detectable low albumin.  This is thought to be due to third spacing. 

Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome.  2013.  Mast cells.
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