Pre- and postpregnancy platelet counts: evaluating accuracy of gestational thrombocytopenia and immune thrombocytopenia purpura diagnoses

Abstract

Given the overlapping clinical indicators and lack of diagnostic testing, misdiagnosis of immune thrombocytopenic purpura and gestational thrombocytopenia in pregnancy may be common. Current recommendations suggest utilizing platelet nadir during pregnancy to guide diagnosis. This study aimed to assess the accuracy of gestational thrombocytopenia and immune thrombocytopenic purpura diagnoses using pre- and postpregnancy platelet counts. This was a retrospective cohort study of patients diagnosed with gestational thrombocytopenia and immune thrombocytopenic purpura from January 2017 to December 2019. Platelet counts were extracted from charts and evaluated at several time periods, namely prepregnancy (within 5 years), during pregnancy, and postpartum (>6 weeks to 5 years). A diagnosis of gestational thrombocytopenia was considered inaccurate if platelet counts were <150,000/µL pre- or postpregnancy with no other apparent causes or if the platelet nadir dropped below 100,000/µL during pregnancy. A diagnosis of immune thrombocytopenic purpura was deemed inaccurate if pre- or postpregnancy platelet counts were >150,000/µL. The primary outcome was accuracy of gestational thrombocytopenia and immune thrombocytopenic purpura diagnoses in patients. Secondary outcomes included mean platelet counts during pregnancy and difference in mean platelet counts for patients with an accurate vs inaccurate diagnosis of gestational thrombocytopenia. Outcomes were summarized with descriptive statistics and compared using Student t tests. A total of 116 patients met the inclusion criteria of which 111 (96%) and 5 (4%) had gestational thrombocytopenia and immune thrombocytopenic purpura diagnoses, respectively. Platelet counts outside of pregnancy were available for 91 (82%) of the patients, and 66 (57%) had prepregnancy platelet counts available. Of the 91 patients, the diagnosis was considered accurate in 61 (67%) and 5 (100%) patients with gestational thrombocytopenia and immune thrombocytopenic purpura, respectively. Conversely, 30 of 35 (86%) patients with immune thrombocytopenic purpura were found to be inaccurately diagnosed with gestational thrombocytopenia after application of platelet thresholds. Among these 30 patients, 10 had a prepregnancy platelet count <150,000/µL, 12 had a postpartum platelet count <150,000/µL, 3 had a platelet count nadir <100,000/µL during pregnancy, and 7 met more than 1 criterion. Pre- and postpregnancy platelet counts and platelet count nadir differed significantly for patients with an accurate vs inaccurate diagnosis of gestational thrombocytopenia (P<.001). When pre- and postpregnancy platelet counts were checked, one-third of cases of gestational thrombocytopenia met the criteria for immune thrombocytopenic purpura and were thus incorrectly diagnosed during pregnancy. Prepregnancy platelet counts, available for most patients, should be considered when diagnosing gestational thrombocytopenia vs immune thrombocytopenic purpura.