Mean platelet diameter measurements to classify inherited thrombocytopenias.

INTRODUCTION: Mean platelet volume (MPV) assists the differential diagnosis of inherited thrombocytopenia (IT) but lacks standardisation and varies between automated analysers. Classification of IT based on mean platelet diameter (MPD) has been proposed by an international collaborative study but has not been validated.

METHODS: To assess the applicability of MPD to classify forms of IT, digital images of blood films from patients with established genetic causes for IT were generated, and the MPD measured (ZEISS Axio-scanner and Image J software) by a blinded reviewer. Comparison was made to the proposed classification system.

RESULTS: Mean platelet volume was measured in thrombocytopenia with different genetic aetiologies, bilallelic BSS (bBSS) (n = 1), monoallelic BSS (mBSS) (n = 2), MYH9-related disorders (MYH9-RD) (n = 11), GFI1B-related thrombocytopenia (RT) (n = 15), FLI1-RT (n = 2), TUBB1-RT (n = 3), ITGA2B/ITGB3-RT (n = 1), RUNX1-RT (n = 2) and controls (n = 54). bBSS and 82% of MYH9-RD samples had MPD >4 μm which correlated with "IT with giant platelets." Only 55% of samples expected in the "large platelet group" had MPD meeting the classification cut-off (MPD >3.2 μm). FLI1-RT MPD were significantly larger than expected whilst ITGA2B/ITGB3-RT MPD were smaller than proposed. MPD in FPD/AML were "normal."

CONCLUSION: Platelet MPD measurements are a useful guide to classify IT, but the time taken to record measurements may limit clinical applicability.