International classification of diseases–9th revision coding for preeclampsia: how accurate is it?

The purpose of this study was to evaluate the accuracy of the International Classification of Diseases–9th revision codes for preeclampsia and eclampsia. The University of Illinois Medical Center at Chicago discharge database was used to identify 135 women from 1999 through 2001 whose disease was coded as having preeclampsia or eclampsia. With American College of Obstetrics and Gynecology criteria as the gold standard, the diagnosis that was determined through chart review was compared with the International Classification of Diseases–9th revision code that was present in the discharge database. Patients were classified as true cases if the International Classification of Diseases–9th revision code matched the American College of Obstetricians and Gynecologists diagnosis; the positive predictive value of the code was then calculated. The overall positive predictive value for the complete sample was only 54%, but the positive predictive value for severe preeclampsia was 84.8%, which was high compared with mild preeclampsia (45.3%) and eclampsia (41.7%). Diagnostic (clinician) error was the most common reason for miscoding error. The findings suggest that International Classification of Diseases–9th revision codes for preeclampsia/eclampsia vary greatly in their accuracy of diagnosis. Therefore, a review of medical records is required when data are being gathered on the incidence of preeclampsia and eclampsia.