A standardized endogenous megakaryocytic erythroid colony assay for the diagnosis of essential thrombocythemia.

BACKGROUND AND OBJECTIVES The reliability of assays of endogenous megakaryocytic colony (EMC) and endogenous erythroid colony (EEC) formation for the diagnosis of thrombocytoses remains controversial. We tested the suitability of a recently developed collagen-based assay of EMC formation for the diagnosis of essential thrombocythemia (ET). DESIGN AND METHODS This was a multicenter (8 laboratories) study including 121 patients: 82 with ET and 39 with reactive thrombocytoses (RT). EMC and EEC were assessed in each laboratory in serum-free, cytokine-free, standardized collagen gel assays; bone marrow (BM) and peripheral blood (PB) were tested in parallel. RESULTS In PB cultures, only EEC were specific for ET. In BM cultures, both EMC and EEC were specific for ET and present in assays of 77.8% (EMC) and 33.3% (EEC) of ET patients. Altogether, 80.2% of ET patients had BM EMC and/or EEC, whereas none of the patients with RT did. INTERPRETATION AND CONCLUSIONS When performed with BM progenitors for the diagnosis of thrombocytoses, positivity of the standardized EMC/EEC assay in collagen is specific (100%) and detects 80% of ET.