Proteinuria and its assessment in normal and hypertensive pregnancy

The purposes of this study were (1) to determine 24-hour urinary protein excretion rates in normal human pregnancy and (2) to assess the reliability of assessment of proteinuria by dipstick measurement.

At 17 to 20 and 33 to 36 weeks of pregnancy, 174 normal volunteers collected a 24-hour urine sample; the volume and the protein and creatinine concentrations were measured. The result for protein was compared with dipstick analysis of an early morning midstream urine sample collected at the conclusion of the 24-hour period. Sixty-eight consecutive inpatients admitted to the antenatal ward with hypertension and positive urine dipstick tests for protein underwent the same procedure. The interobserver variability in dipstick analyses of urine samples of known protein content was assessed with the aid of 66 volunteers from the hospital staff.

The upper 95% confidence limit of the normal population was less than 200 mg per 24 hours, at both stages of pregnancy investigated. In these women and in the hypertensive inpatients a high proportion of false-positive and false-negative results was found with dipstick analyses. Interobserver variation in assessment of proteinuria by dipstick was high, with an 18% false-positive rate and a false-negative rate approaching 40% for samples with 30 mg/dl. Even in the presence of 100 mg/dl the false-negative rate was 7%, whereas the concentration of protein was significantly underestimated in 20% of samples with 500 mg/dl.

Dipstick urinalysis cannot be relied on either to detect or to exclude the presence of proteinuria in pregnant women.