The sensitivity and specificity of platelet autoantibody testing in immune thrombocytopenia: a systematic review and meta-analysis of a diagnostic test

The diagnosis of ITP is based on a platelet count<100x10(9)L(-1) and exclusion of other causes. There are no standard tests or biomarkers to diagnose ITP. The sensitivity of platelet autoantibody testing is low (53%). The specificity is high (>90%). A positive autoantibody test can be useful to rule in ITP but a negative does not rule out ITP. Summary Background Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by a low platelet count and an increased risk of bleeding. The sensitivity and specificity of platelet autoantibody tests is variable and their utility is uncertain. Objective The purpose of this study was to perform a systematic review and meta-analysis of platelet autoantibody tests in the diagnosis of ITP. Methods Ovid Medline, PubMed, and Web of Science were searched from inception until 31 May 2018. Two reviewers independently assessed studies for eligibility and extracted data. Studies that reported testing results for antiplatelet autoantibodies on platelets (direct tests) or in plasma/serum (indirect tests) for 20 or more ITP patients were included. Results Pooled estimates for sensitivity and specificity were calculated using a random effects model. Pooled estimates for the sensitivity and specificity of direct anti-platelet autoantibody testing for either anti-glycoprotein IIbIIIa or anti-glycoprotein IbIX were 53% (95% confidence interval [CI], 44-61%) and 93% (95% CI, 81-99%), respectively. For indirect testing, the pooled estimates for the sensitivity and specificity were 18% (95% CI, 12-24%) and 96% (95% CI, 87-100%), respectively. Conclusions Autoantibody testing in ITP patients has a high specificity but low sensitivity. A positive autoantibody test can be useful for ruling in ITP, but a negative test does not rule out ITP.