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 pre-eclampsia 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 pre-eclampsia, 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.