Challenges in applying diagnostic criteria for systemic mastocytosis

Systemic mastocytosis (SM), first reported in 1949 1 and defined by the World Health Organization (WHO) classification, 2 can be challenging to diagnose.4][5][6][7][8] Testing methodology has been improved over time, but challenges remain.We present 15 cases in which resolution of discrepant laboratory results was needed to establish a diagnosis.We retrospectively identified patients from a MC registry 9 who underwent evaluation for SM using 2017 WHO criteria 2 and tryptase genotyping for hereditary-α tryptasemia (HαT) 10 and met at least 1 of following 4 criteria: (1) ≥2 methods of KIT p.D816V testing had discordant results, (2) basal serum tryptase (BST) values were variably >20 ng/mL, (3) there were discordant results of MC CD25 expression assessed using FC and IHC or among clinical laboratories for IHC alone, or (4) there were <25% spindled MCs or <2 MC aggregates in patients meeting other diagnostic criteria.