High-sensitivity flow cytometric analysis of mast cell clustering in systemic mastocytosis: a quantitative and statistical analysis.

We characterized recently identified event clusters in systemic mastocytosis (SM) by calculating the coefficient of variation (CV, %) of CD117 and side scatter (SSC), based on the mean fluorescence intensity of mast cells using flow cytometry. Seventy-five samples were from patients with SM and 124 samples from patients negative for SM (non-SM). Discrete cluster formation seen in 50 cases correlated with significantly lower CV for SSC (46.1% vs. 61.0%, p < 0.0001) and CD117 (64.5% vs. 80.5%, p < 0.0001) for SM vs. non-SM samples. A combined CVCD117 + SSC of < 125 showed a sensitivity of 80% and specificity of 80% for SM with PPV of 67% and NPV of 80%. Probability scores of having SM, generated based on CVs for SSC and CD117, were significantly higher in patients with SM than non-SM (0.55 vs. 0.17, respectively; p < 0.001). Flow cytometric-based quantitative analysis of event clustering is a useful approach for diagnosing and monitoring patients with SM.