Distinguishing Between TTP-HUS and DIC Platelet Count and Prothrombin Time Help Distinguish Thrombotic Thrombocytopenic Purpura-Hemolytic Uremic Syndrome From Disseminated Intravascular Coagulation in Adults

Background: The microangiopathic hemolytic anemias, thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS), and disseminated intravascular coagulation (DIC) are life-threatening conditions with significant clinical overlap. Although TTP is classically described by a pentad of signs, the more likely clinical scenario involves a patient with unexplained thrombocytopenia and hemolytic anemia. TTP is often fatal without therapeutic plasma exchange (TPE). Regarding HUS, the tendency is to use the term TTPHUS and treat with TPE. Acute DIC is the most difficult differential diagnosis to distinguish from TTP-HUS, as it may present with the complete pentad of signs. Testing for TTP-HUS includes ADAMTS13 activity, which should be low in TTP. However, this test is not sensitive enough to identify every patient who will benefit from TPE, and the assay is available primarily in reference laboratories, which precludes appropriate turn-aroundtimes. Objective: To evaluate which routine laboratory tests could differentiate between TTP-HUS and DIC. Design: This was a retrospective case-controlled study. Methods: Each identified patient with TTP-HUS was matched with up to 2 control patients with DIC. All patients had the same admission laboratory tests, which included a CBC, prothrombin time (PT), partial prothrombin time (PTT), D-dimer, creatinine, and LDH. Statistical analysis was then performed. Results: 27 adults with TTP-HUS and 51 control patients with DIC were identified. On univariate analysis, platelet count, PT, INR, and PTT were all statistically significant (P <0.05) between TTP-HUS and DIC. However, after multivariate analysis, only PT and the degree of thrombocytopenia remained associated with TTP-HUS. A platelet count of <20 x 103/μL and a PT within 5 seconds of the upper limit for the reference interval had a sensitivity of only 52% but a specificity of 92%. Conclusions: Readily available laboratory tests, especially platelet counts and PT, help differentiate TTPHUS from DIC in the right clinical scenario, and may help guide proper referral for therapeutic plasma exchange during an acute presentation. Reviewer's Comments: This article addresses the emergency clinical differential diagnosis between TTPHUS and DIC and how routine laboratory tests, such as platelet count and PT, may help guide the clinician toward one or the other diagnosis. As described in the article, at the University of Virginia we often test for ADAMTS13 activity in patients suspected of having TTP-HUS. However, we also send this test out to a reference laboratory. Therefore, this is not a test that is able to be used in the acute setting, which has implications as to whether the patient will get therapeutic plasma exchange. (Reviewer-William A. Kanner, MD).