Problems in methods for the detection of significant proteinuria in pregnancy

The aim of this study was to underscore problems associated with the dipstick test and determination of protein concentration alone in spot-urine (P-test) compared with spot-urine protein-to-creatinine ratio (P/Cr test) and to determine whether urine collection for 24-h test was complete.

Dipstick and P/Cr tests were performed simultaneously in 357 random spot-urine specimens from 145 pregnant women, including 35 with pre-eclampsia. Positive results were defined as ≥ 1+ on dipstick test, protein concentration ≥ 30 mg/dL on P-test, and P/Cr ratio ≥ 0.27 (mg/mg) on P/Cr test. Sixty-four 24-h urine tests (quantification of protein in urine collected during 24 h) were performed in 27 of the 145 women. We assumed that P/Cr ratio ≥ 0.27 predicted significant proteinuria (urinary protein ≥ 0.3 g/day). The 24-h urine collection was considered incomplete when urinary creatinine excretion was <11.0 mg/kg/day or >25.0 mg/kg/day.

Forty-four percent (69/156) of specimens with a positive test result on dipstick test contained protein < 30 mg/dL. Dipstick test was positive for 25.7% (69/269) of specimens with protein < 30 mg/dL and for 28.8% (79/274) of specimens with P/Cr ratio < 0.27. P-test results were positive for 7.3% (20/274) and negative for 18.1% (15/83) of specimens with P/Cr ratio < 0.27 and ≥ 0.27, respectively. Incomplete 24-h urine collection occurred in 15.6% (10/64) of 24-h urine tests. Daily urinary creatinine excretion was 702-1397 mg, while creatinine concentration varied from 16 mg/dL to 475 mg/dL in spot-urine specimens.

Dipstick test and P-test were likely to over- and underestimate risks of significant proteinuria, respectively. The 24-h urine collection was often incomplete.