Received on March 25, 2007
Accepted on July 2, 2007

Evidence-based Medicine and Test Utilization

Protein:Creatinine Ratio in Random Urine Samples Is a Reliable Marker of Increased 24-Hour Protein Excretion in Hospitalized Women with Hypertensive Disorders of Pregnancy

¹ Research Unit in Reproductive Medicine, México, D.F. México
² Department of Hypertensive Diseases of Pregnancy Clinic, Hospital de Ginecología y Obstetricia "Luis Castelazo Ayala", Instituto Mexicano del Seguro Social, México, D.F. México

^* To whom correspondence should be addressed. E-mail: alfredolm{at}yahoo.com.

Background: The protein:creatinine ratio in random, untimed urine samples correlates with 24-h protein excretion in pregnant women with and without hypertension. Nevertheless, whether this ratio is appropriate as a screening test for proteinuria is still unclear, in part because of the paucity of large studies.

Methods: We measured protein:creatinine ratios in random urine samples and protein contents of 24-h urine samples in a cross-sectional study of 927 hospitalized pregnant women at 20-weeks of gestational age and in a 2nd cohort of 161 pregnant women. In the 2nd group, urine specimens were obtained before and after completion of the 24-h collections, avoiding 1st-morning void specimens.

Results: Protein excretion was 300 mg/24 h in 282 patients (30.4%). The urine protein:creatinine ratio and the 24-h protein excretion were significantly correlated (r = 0.98, P <0.001). The protein:creatinine ratio as an indicator of protein excretion >300 mg/24 h was 0.3. The sensitivity and specificity were 98.2% and 98.8%, respectively. Positive and negative predictive values were 97.2% and 99.2%, respectively, and positive and negative likelihood ratios were 79.2 and 0.02, respectively. The diagnostic accuracy of the urinary protein:creatinine ratio was corroborated in the 2nd cohort of patients, which also showed no statistically significant difference in protein:creatinine ratio between samples obtained >24 h apart.

Conclusions: Random urinary protein:creatinine ratio is a reliable indicator of significant proteinuria (>300 mg/day) in nonambulatory pregnant women, irrespective of sampling time during the daytime. The protein:creatinine ratio may be reasonably used as an alternative to the 24-h urine collection method.