BACKGROUND: Although qualitative tests are often used for urinary protein evaluation in primary care and health checkups, their results are affected by urine concentration, and the possibility of false-positive or false-negative results can hinder appropriate referral to a nephrologist. We aimed to investigate whether the consideration of urine specific gravity (uSG) improves the diagnostic performance of proteinuria evaluation using qualitative analysis. METHODS: Urine protein levels (mg/gCr), qualitative data, and uSG were extracted over the past 5 years in our nephrology outpatient department. Qualitative results were classified as (-) to (4+), quantitative as A1 <
150, A2 <
500, A3 ≥ 500, A4 ≥ 1000. The second test was performed 1 year later. RESULTS: In total, 37% of (-) were A2 or higher and 14% of (±) were A3 or higher. In (±), 57% in uSG <
1.010 was A3 or higher, and 72% in uSG >
1.020 was A1. The AUC, with urine specific gravity as the explanatory variable and proteinuria of A2 or higher as the outcome, was 0.878 (95% CI 0.871-0.884). The result did not change significantly even after excluding severe hematuria, multiple myeloma and urine pH ≥ 7.5. The percentage of A1 was 37% for the first quantification of two consecutive (±) and 31% for only one (±). CONCLUSION: Current qualitative tests can overestimate or underestimate the actual urinary protein levels. Consideration should be given to increasing the diagnostic performance of qualitative tests in combination with uSG.