Rising total leukocyte counts correspond with rising platelet counts in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare disorder involving pathological platelet-von Willebrand factor interaction, resulting in microvascular thrombosis. The consumption of platelets in TTP microthrombi results in severe thrombocytopenia which resolves with resolution of the microvascular thrombosis. Over the course of treatment, patient platelet counts often rise and fall multiple times before stable remission is achieved. On casual inspection, we noted that total leukocyte counts follow a pattern that appears to correspond to platelet counts. To explore whether changing leukocyte counts track significantly with changing platelet counts, we examined paired daily platelet counts and total leukocyte counts in 27 episodes of TTP in 13 patients across 2 institutions comprising 423 days of data. We modeled the nonlinear behavior in the data using a threshold mixed-effects regression model, in which we found a significant temporal relationship between total leukocyte counts and platelet counts. The model proved that, on a day when platelet counts were rising in previous days, the total leukocyte count is predictive of the rise in platelet count. The higher the total leukocyte count, the greater the rise in platelet count. Our results support the hypothesis that leukocytes play a role in the resolution of TTP microvascular thrombosis.