Correlation of blood counts with vascular complications in essential thrombocythemia: analysis of the prospective PT1 cohort

Abstract

Essential thrombocythemia, a myeloproliferative neoplasm, is associated with increased platelet count and risk of thrombosis or hemorrhage. Cytoreductive therapy aims to normalize platelet counts despite there being only a minimal association between platelet count and complication rates. Evidence is increasing for a correlation between WBC count and thrombosis, but prospective data are lacking. In the present study, we investigated the relationship between vascular complications and 21 887 longitudinal blood counts in a prospective, multicenter cohort of 776 essential thrombocythemia patients. After correction for confounding variables, no association was seen between blood counts at diagnosis and future complications. However, platelet count outside of the normal range during follow-up was associated with an immediate risk of major hemorrhage (P = .0005) but not thrombosis (P = .7). Elevated WBC count during follow-up was correlated with thrombosis (P = .05) and major hemorrhage (P = .01). These data imply that the aim of cytoreduction in essential thrombocythemia should be to keep the platelet count, and arguably the WBC count, within the normal range. This study is registered at the International Standard Randomized Controlled Trials Number Registry (www.isrctn.org) as number 72251782.

Figure 1

Relationship between blood counts during follow-up and risk of thrombosis. The curve of best fit is shown as a thick green line with the 95% confidence intervals for the curve shown as thin green lines. A hazard ratio of 1 (dashed line) indicates no increased risk of thrombosis, whereas > 1 indicates increased risk. Counts at which events occurred are marked with an orange line above the x axis; counts at which no events occurred are marked with black ticks. Curves are shown for platelet count (A), WBC count (B), and Hb concentration (C).

Figure 2

Relationship between blood counts during follow-up and risk of major hemorrhage. The curve of best fit is shown as a thick green line with the 95% confidence intervals for the curve shown as thin green lines. A hazard ratio of 1 (dashed line) indicates no increased risk of thrombosis, whereas > 1 indicates increased risk. Counts at which events occurred are marked with an orange line above the x axis; counts at which no events occurred are marked with black ticks. Curves are shown for platelet count (A), WBC count (B), and Hb concentration (C).