Laboratory Testing for Suspected Mast Cell Disorders

Initial Laboratory Workup

The National Comprehensive Cancer Network recommends starting with serum tryptase measurement and peripheral blood KIT D816V mutation testing using highly sensitive ASO-qPCR, followed by bone marrow biopsy if tryptase is persistently >20 ng/mL or if systemic mastocytosis is suspected 1, 2, 3
For all patients with suspected mast cell disorders, the National Comprehensive Cancer Network suggests obtaining baseline tests, including serum tryptase, peripheral blood KIT D816V mutation, complete blood count with differential, and 24-hour urine collection for N-methylhistamine, leukotriene E4, and 11β-prostaglandin F2α 3, 4

The National Comprehensive Cancer Network recommends obtaining acute serum tryptase 1-4 hours after symptom onset during an active episode, with a diagnostic threshold of ≥20% increase above the patient's baseline tryptase PLUS an absolute increase of ≥2 ng/mL 3, 4

The National Comprehensive Cancer Network suggests proceeding to bone marrow biopsy and aspirate when baseline serum tryptase persistently >20 ng/mL, peripheral blood KIT D816V mutation is positive, or clinical features suggest systemic mastocytosis 1, 2, 4
Bone marrow analysis must include core biopsy, immunohistochemistry, flow cytometry, KIT D816V mutation analysis, reticulin and collagen staining, and chromosome analysis 1, 2

The National Comprehensive Cancer Network recommends testing for FIP1L1-PDGFRA fusion gene to exclude hypereosinophilic syndrome variants in patients with interstitial mast cell pattern, peripheral eosinophilia, and negative KIT D816V 1, 2
The National Comprehensive Cancer Network suggests evaluating for alternative codon 816 mutations or mutations in other KIT regions if KIT D816V remains negative despite high mast cell burden 1, 2

ASO-qPCR detects KIT D816V in >80% of systemic mastocytosis patients when applied to bone marrow, with limitations including false-negative results due to low mast cell burden or presence of other KIT mutations 1, 2
Next-generation sequencing myeloid panels have only ~5% sensitivity for KIT D816V and are NOT recommended for this purpose 1, 2