Objective 1) To assess the correlation between urine albumin/creatinine ratio (ACR) and 24-hour urine albumin excretion in women with pre-eclampsia, 2) to study the influence of potential confounders on this correlation and 3) to assess the variability of ACR between voids during a 24-hour period.
Design Prospective study.
Setting Fetal maternity ward, university hospital.
Population Women with pre-eclampsia scheduled for quantitative albumin measurement with a 24-hour urine collection.
Methods Random urine samples were obtained for analysis of ACRs during the time of 24-hour urine collections in 31 women. ACRs were also measured from the complete 24-hour collections. In five additional women, serial urine samples were obtained during the 24-hour collection.
Main outcome measures Correlation between ACRs and albumin amount in 24-hour urine samples. Variability of the ACRs during a 24-hour collection.
Results The random ACR was poorly correlated to 24-hour excretion of urine albumin (R2= 0.42). Adjustment for maternal age and nifedipine medication significantly (P= 0.044 and P= 0.023, respectively) improved the correlation (R2= 0.60). The mean variability (highest/lowest) of ACR during a 24-hour period was 222%. The ACR from the 24-hour collection had an excellent correlation to 24-hour excretion of urine albumin (R2= 0.96).
Conclusions In women with pre-eclampsia, random ACR is not stable during the day and cannot predict 24-hour urine protein excretion accurately. ACR from the 24-hour collection is an accurate predictor of total albumin amount and can be used to minimise errors from incomplete collections.