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Keywords:

  • creatinine in the urine;
  • protein-to-creatinine ratio;
  • proteinuria

Abstract

Aim

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.

Material and Methods

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.

Results

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.

Conclusion

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