Elevated Red Cell Distribution Width in the Diagnosis of Thrombotic Thrombocytopenic Purpura in Patients Presenting with Anemia and Thrombocytopenia

OBJECTIVE: To determine if red cell distribution width (RDW) is elevated in thrombotic thrombocytopenic purpura (TTP) and to evaluate the sensitivity and specificity of such elevation in the diagnosis of TTP. METHODS: We retrospectively studied red cell distribution width at presentation in 25 consecutive patients with newly diagnosed TTP who were treated with plasmapheresis in our institution between 1997 to 2005. Control patients consisted of 20 consecutive patients without TTP who presented to the emergency room (ER) with anemia and thrombocytopenia. RESULTS: Patients with TTP had significantly elevated RDW compared with the controls (23.1% versus 17.2% respectively, P = 0.0001). An RDW > 18% had a 95% sensitivity and 70% specificity in the diagnosis of TTP, whereas RDW > 19% had 80% sensitivity and 85% specificity. CONCLUSIONS: TTP should be suspected in patients presenting with unexplained anemia and thrombocytopenia with an RDW > or = 18%.