Comparison of Proteinuria Determination by Urine Dipstick, Spot Urine Protein Creatinine Index, and Urine Protein 24 Hours in Lupus Patients

Abstract

A simple, convenient, and accurate method for detecting urine protein excretion in lupus nephritis is crucial. The objectives of the study were to determine the sensitivity and the specificity of the qualitative urine dipstick test value to detect 0.50 g or greater of the quantitative 24-hour urine protein (24-hUP) in lupus patients, to evaluate an overall agreement of the dipstick test results and the magnitude of 24-hUP, and to examine the correlation between the spot urine protein creatinine index (S-UPCI) and the 24-hour UPCI with that of the 24-hUP. A prospective study was conducted in 92 patients with lupus. All dipstick test values from 5 dipstick assays (Bayer, Roche, Meditest USA, Standard Diagnostics, and Arkray) and the S-UPCI were obtained within 6 hours of the 24-hUP collection. Of 149 urine samples, only 39% were collected properly and were used for analysis. The sensitivity and specificity of a ≥ 2+ dipstick test result to detect 0.50 g or greater 24-hUP were 56-% to 80% and 67% to 92%, respectively. The agreement of the urine dipstick test values and the magnitude of 24-hUP was fair (κ = 0.23-0.32). The correlation between the S-UPCI and the 24-hUP was 0.83 (P < 0.0001), and that of the 24-hour UPCI and the 24-hUP was 1 (P < 0.0001). Using 24-hUP 2 g/d or less, the bias ± 1.96 SD of the difference of S-UPCI and 24-hUP was 0.23 (SD, 0.96) g. A ≥ 2+ dipstick test is relatively sensitive to detect significant proteinuria, but it is poorly correlated with quantitative 24-hUP. The S-UPCI and the 24-hUP can be used interchangeably for follow-up in lupus nephritis patients with proteinuria of less than 2 g/d.