Liver function tests in pre-eclampsia: Importance of comparison with a reference range derived for normal pregnancy

Objectives To determine reference ranges for liver function tests in uncomplicated pregnancy and to relate abnormal results by these criteria to outcome in pre-eclampsia. Design Prospective, cross-sectional study to establish the reference ranges. Prospective observational study of women with pre-eclampsia. Setting Antenatal clinics and obstetric unit of St Mary's Hospital, London. Participants Four hundred and thirty women with uncomplicated pregnancies and 85 consecutive women with gestational hypertension. Main outcome measures Aspartate transaminase (AST), alanine transaminase (ALT), bilirubin and gamma glutamyl transferase (GGT) were measured to determine their ranges in normal pregnancy. The severity of pre-eclampsia was determined by the maximum blood pressure, creatinine and 24 h urinary protein; minimum platelet count; maternal complications; mode of and gestation at delivery; and fetal outcome with centile weight adjusted for gestational age and sex. Results AST, ALT, bilirubin and GGT were each lower in uncomplicated pregnancy than the nonpregnant laboratory reference ranges. Of those cases with elevated liver function tests in the preeclampsia group, 37% were abnormal only by the new reference ranges. Using the new ranges, the prevalence of elevated liver function tests was significantly higher in the pre-eclampsia group (54%) than in those with pregnancy induced hypertension (14%) (P < 0.01). Amongst those with preeclampsia, abnormal liver function tests were associated with greater proteinuria (P < 0.05), lower platelet count (P < 0.001) and more maternal complications (P < 0.01) than normal liver function tests; there was no difference in the severity of hypertension between the groups. Conclusions Liver function tests are lower in normal pregnancy than the reference ranges currently used. Our pregnancy-derived ranges allow more precise identification of abnormal liver function in women with pre-eclampsia than is possible using standard reference ranges derived from a nonpregnant population.