From the Guidelines
Serum tryptase level is the recommended initial screening test for mastocytosis, and a persistently elevated tryptase level (>20 ng/mL) strongly suggests mastocytosis and warrants further investigation. The test measures the amount of tryptase enzyme released by mast cells, which is typically elevated when there is an abnormal proliferation of these cells. Additional screening may include a complete blood count, liver function tests, and bone marrow examination in suspected cases. For cutaneous mastocytosis, a skin biopsy may be performed. The 24-hour urine collection for N-methylhistamine or prostaglandin D2 metabolites can also help detect increased mast cell activity.
Key Points to Consider
- Mastocytosis can present with vague symptoms like flushing, abdominal pain, and hypotension that mimic other conditions, making early detection crucial 1.
- The diagnosis of mastocytosis and its subtypes is based on the 2017 WHO Criteria Classification and requires a combination of histopathologic, clinical, laboratory, and cytogenetic/molecular analyses 1.
- Allele-specific oligonucleotide quantitative reverse transcriptase polymerase chain reaction (ASO-qPCR) is a highly sensitive assay for detecting the KIT D816V mutation, which is found in >80% of patients with systemic mastocytosis 1.
- In patients with a high mast cell burden and a negative KIT D816V screen, the result should be confirmed with the most sensitive technique available, ASO-qPCR, if not originally obtained with this technique 1.
- Multidisciplinary collaboration with sub-specialists is recommended for the management of patients with mastocytosis, and participation in clinical trials is especially encouraged 1.
From the Research
Screening Tests for Mastocytosis
- The detection of serum tryptase, an essential mast cell enzyme, is a widely used tool in the diagnosis of mastocytosis 2.
- Bone marrow tryptase level has been evaluated as a possible diagnostic criterion for adult systemic mastocytosis, with a cut-off value of 50 μg/L identifying systemic mastocytosis with a sensitivity of 93.0% and a specificity of 90.0% 3.
- Basal serum tryptase (BST) ≥11.5 and ≥20.0 ng/mL, REMA ≥2, monomorphic maculopapular CM (MPCM), and elevated BST based upon tryptase genotype are individual and combined screening tests for systemic mastocytosis, with elevated BST based upon genotype having the highest sensitivity at 84.2% 4.
- Minor diagnostic criteria for systemic mastocytosis include elevated serum tryptase level, abnormal MC CD25 expression, and presence of KITD816V mutation 5, 6.
Diagnostic Criteria
- The major criterion for systemic mastocytosis is the presence of multifocal clusters of abnormal mast cells in the bone marrow 5, 6.
- Establishing SM subtype as per the World Health Organization classification system is an important first step in diagnosis and treatment 5, 6.