Accuracy of serum uric acid in predicting complications of pre-eclampsia: a systematic review

BACKGROUND: Pre-eclampsia is one of the largest causes of maternal and fetal mortality and morbidity. Hyperuricemia is often associated with pre-eclampsia. OBJECTIVE: To determine the accuracy with which serum uric acid predicts maternal and fetal complications in women with pre-eclampsia. STUDY DESIGN: Systematic quantitative review of test accuracy studies. SEARCH STRATEGY: We conducted electronic searches in MEDLINE (1951-2004), EMBASE (1980-2004), the Cochrane Library (2004:4) and the MEDION database to identify relevant articles. A hand-search of selected specialist journals and reference lists of articles obtained was then carried out. There were no language restrictions for any of these searches. SELECTION CRITERIA: Two reviewers independently selected the articles in which the accuracy of serum uric acid was evaluated to predict maternal and fetal complications of pre-eclampsia. DATA COLLECTION AND ANALYSIS: Data were extracted on study characteristics, quality and accuracy to construct 2 x 2 tables with maternal and fetal complications as reference standard. Summary likelihood ratios for positive (LR+) and negative LR(-) test results are generated for various threshold levels of uric acid. MAIN RESULTS: There were 18 primary articles that met the selection criteria, including a total of 3913 women and forty-one 2 x 2 tables. In women with pre-eclampsia, a positive test result of uric acid greater than or equal to a 350-micromol/l threshold predicted eclampsia with a pooled likelihood ratio (LR) of 2.1 (95% CI 1.4-3.5), while a negative test result had a pooled LR of 0.38 (95% CI 0.18-0.81). For severe hypertension as the outcome measure, the LRs were 1.7 (95% CI 1.3-2.2) and 0.49 (95% CI 0.38-0.64) for positive and negative test results, respectively, and for caesarean section the LRs were 2.4 (95% CI 1.3-4.7) and 0.39 (95% CI 0.20-0.76). For stillbirths and neonatal deaths the respective LRs were 1.5 (95% CI 0.91-2.6) and 0.51 (95% CI 0.20-1.3). For the prediction of small-for-gestational-age fetus, the pooled LRs were 1.3 (95% CI 1.1-1.7) and 0.60 (95% CI 0.43-0.83) for positive and negative results, respectively. AUTHOR'S CONCLUSION: Serum uric acid is a poor predictor of maternal and fetal complications in women with pre-eclampsia.