Specific Gravity Improves Identification of Clinically Significant Quantitative Proteinuria from the Dipstick Urinalysis.

BACKGROUND:CKD is often underdiagnosed during early stages when GFR is preserved due to underutilization of testing for quantitative urine albumin-to-creatinine ratio (UACR) or protein-to-creatinine ratio (UPCR). Semi-quantitative dipstick proteinuria (DSP) on urinalysis is widely obtained but not accurate for identifying clinically significant proteinuria. METHODS:We identified all patients with a urinalysis and UACR or UPCR obtained on the same day at a tertiary referral center. The accuracy of DSP alone or in combination with specific gravity against a gold-standard of UACR ≥30 mg/g or UPCR ≥0.15 g/g, characterizing clinically significant proteinuria, was evaluated using logistic regression. Models were internally validated using 10-fold cross validation. The specific gravity for each DSP above which significant proteinuria is unlikely was determined. RESULTS:Of 11,229 patients, clinically significant proteinuria was present in 4,073 (36%). The area under the receiver operating characteristic curve (95% confidence interval) was 0.77 (0.76, 0.77) using DSP alone and 0.82 (0.82, 0.83) in combination with specific gravity (P<0.001), yielding a specificity of 0.93 (standard error, SE=0.02) and positive likelihood ratio of 9.52 (SE=0.85). The optimal specific gravity cut-offs to identify significant proteinuria were ≤1.0012, 1.0238, and 1.0442, for DSP of trace, 30, and 100 mg/dL. At any specific gravity, a DSP ≥300 mg/dL was extremely likely to represent significant proteinuria. CONCLUSION:Adding specific gravity to DSP improves recognition of clinically significant proteinuria and can be easily used to identify patients with early-stage CKD who may not have otherwise received a quantified proteinuria measurement for both clinical and research purposes.