A Clinically Applicable Model Using Blood Counts to Support the Diagnosis of Prefibrotic Myelofibrosis Versus Essential Thrombocythemia

This study aimed to distinguish between essential thrombocythemia (ET) and prefibrotic primary myelofibrosis (pre-PMF) using routine blood tests, with a focus on white blood cell (WBC) and platelet (PLT) levels. We evaluated the predicted probability of a pre-PMF diagnosis based on the interaction between WBC and PLT levels using data from a logistic regression model involving 891 patients with ET and 180 patients with pre-PMF. Patients were divided into four groups based on whether their WBC and PLT values were below or above the respective thresholds of 8.85 × 10⁹/L and 793 × 10⁹/L. The results showed that patients with low levels of both WBCs and PLTs had the lowest predicted probability of pre-PMF (6%), indicating a profile more typical of ET. When either WBC or PLT levels were elevated, the probability increased to approximately 18%–19%, indicating a potential shift toward pre-PMF features. Notably, patients with elevated levels of both WBCs and PLTs had the highest probability of a pre-PMF diagnosis (26%), which was more than four times higher than that of the low–low group. The association between combined WBC/PLT levels and a pre-PMF diagnosis remained significant (p < 0.001), even when adjusting for serum lactate dehydrogenase (LDH) and splenomegaly. These findings suggest that elevated WBC and PLT levels together can serve as a practical and accessible diagnostic tool for supporting the differential diagnosis of ET or pre-PMF in cases of uncertainty, and for deferring bone marrow biopsy in cases of early disease presenting with isolated thrombocytosis.