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 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 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: http://www.phadia.com/Global/Market%20Companies/Sweden/Best%C3%A4ll%20information/Filer%20(pdf)/ImmunoCAP_Tryptase_anafylaxi.pdf
[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.