Table 2.

Criteria for B and C findings according to the updated 2016 WHO classification

B findings
−	High MC burden (shown on BM biopsy): >30% infiltration of cellularity by MCs (focal, dense aggregates) and serum total tryptase >200 ng/mL
−	Signs of dysplasia or myeloproliferation, in non-MC lineage(s), but criteria are not met for definitive diagnosis of an AHN, with normal or only slightly abnormal blood counts
−	Hepatomegaly without impairment of liver function, palpable splenomegaly without hypersplenism and/or lymphadenopathy on palpation or imaging
C findings
−	BM dysfunction caused by neoplastic MC infiltration, manifested by ≥1 cytopenia: absolute neutrophil count <1.0 × 109/L, hemoglobin level <10 g/dL, and/or platelet count <100 × 109/L
−	Palpable hepatomegaly with impairment of liver function, ascites, and/or portal hypertension
−	Skeletal involvement, with large osteolytic lesions with or without pathologic fractures*
−	Palpable splenomegaly with hypersplenism
−	Malabsorption with weight loss due to gastrointestinal tract MC infiltrates

^*Pathological fractures caused by osteoporosis do not qualify as a C finding. WHO, World Health Organization; MC, mast cell; BM, bone marrow; AHN, associated hematological neoplasm.