Reducing unnecessary coagulation testing in hypertensive disorders of pregnancy

Abstract

Objective: To estimate the magnitude of laboratory testing for hypertension in pregnancy and determine whether abnormalities in prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen can be predicted by results of common, less expensive tests. Materials and Methods: Laboratory records were searched and charts were reviewed to identify gravidas tested for hypertension and to exclude conditions producing coagulopathy. Contingency tables were constructed to assess the ability of the platelet count, lactate dehydrogenase, and transaminases to predict coagulation test results. Results: Preliminary data on 73 gravidas found that a platelet count plus a lactate dehydrogenase test best predicted coagulation abnormalities. Results on another 732 gravidas indicated that coagulation tests were obtained in about 30%. No patient had a PT greater than 18 seconds, two had an aPTT greater than 40 seconds, and three had fibrinogen levels less than 200 mg/dL. The combination of a normal platelet count plus a normal lactate dehydrogenase had a negative predictive value of 100% for clinically significant abnormalities of PT and aPTT, and 99% for significant abnormalities of fibrinogen. Conclusions: Substantial coagulation testing was done on gravidas evaluated for a hypertensive disorder even though the prevalence of clinically significant abnormalities was low. Laboratory evaluation of patients suspected of having preeclampsia need not include a PT, aPTT, or fibrinogen test when there is no evidence of bleeding or of a condition that could produce coagulopathy and when the platelet count and lactate dehydrogenase level are both normal.