Comparison of Urine Dipstick for Proteinuria with Urine Albumin–Creatinine Ratio

抄録

Objective: Evaluation of proteinuria is essential for diagnosing and grading chronic kidney disease. However, subjects whose urine dipstick test for proteinuria is positive in annual health check-ups are often diagnosed as negative in quantitative reexamination. We therefore investigated discrepancies between the results of urine dipstick testing for proteinuria and urinary albumin-to-creatinine ratio (U-ACR).

Methods: Urine samples were taken from 18,363 subjects who underwent annual health check-ups in 2018. We compared the results of urine dipstick for proteinuria with U-ACR, and calculated the specificity, sensitivity, and area under the curve (AUC) of the receiver-operating-characteristic curve of urine dipstick for proteinuria for U-ACR by quintiles of urine gravity.

Results: In samples of dipstick (−) for proteinuria, 1.6% presented micro- and overt albuminuria. In samples of dipstick (±) for proteinuria, 94.8% showed normo-albuminuria. In samples of dipstick (1+) and (2+) for proteinuria, the prevalences of normo-albuminuria were 61.7% and 14.6%, respectively. With higher quintiles of urine-specific gravity, the specificity of the dipstick test for proteinuria sharply declined, and AUC values were lower. In the lowest category of urine specific gravity, the specificity of the dipstick test for proteinuria was high, but the sensitivity was low.

Conclusion: Discrepancies were observed between the results of urine dipstick test for proteinuria and U-ACR. In dilute urine, the probability of false-negative results was high. With more concentrated urine, the probability of false-positive results increased. Given these diagnostic pitfalls, urine dipstick test for proteinuria is problematic, therefore, U-ACR is recommended in annual health checkups.