Clinical utility of investigations in triple‐negative thrombocytosis: A real‐world, multicentre evaluation of UK practice

Summary Diagnosis of essential thrombocythaemia (ET) is challenging in patients lacking JAK2 / CALR / MPL mutations. In a retrospective evaluation of 320 patients with ‘triple‐negative thrombocytosis’, we assessed utility of bone marrow histology (90.9% of patients) and myeloid gene panel (MGP, 55.6%). Supportive histology (‘myeloproliferative neoplasm‐definite/probable’, 36.8%) was associated with higher platelet counts and varied between centres. 14.6% MGP revealed significant variants: 3.4% JAK2 / CALR / MPL and 11.2% other myeloid genes. Final clinical diagnosis was strongly predicted by histology, not MGP. 23.7% received cytoreduction (17.6% under 60 years). Real‐world ‘triple‐negative’ ET diagnosis currently depends heavily on histology; we advocate caution in MGP‐negative cases and that specific guidelines are needed.