Table 2.

Biomarkers indicating systemic severe mast cell activation in patients

Biomarker	Specificity for	Sensitivity in	Commonly used in
	mast cells	anaphylaxis	daily practice
Tryptase	+ +*	+**	++
Plasma histamine	+/-	+	+
Urinary histamine metabolites***	+/-	++	++
Prostaglandin D2 metabolites****	+/-	++	+
Urinary cysLT levels	-/+	++	+/-
Heparin	+++	-/+*****	-

Table 2 was reproduced with slight modifications from Valent et al., Int Arch Allergy Immunol [48] with the Editor´s permission

*Basophils express very low amounts of tryptase – but mast cells are a primary and major source of the enzyme; **The relatively low sensitivity of tryptase qualifies as a biomarker of massive mast cell activation and thus as a criterion of MCAS; ***Relevant 24-h urinary histamine metabolites include N-methylhistamine and N-methylimidazoleacetic acid; ****Among prostaglandin D2 metabolites the most commonly measured substance is urinary 11β-prostaglandinF2α; *****An increase in heparin is usually not measurable during an anaphylactic episode, unless the burden of mast cells is very high (like in mast cell leukemia). Abbreviations: cysLT, cysteinyl leukotriene