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Comparative Study
. 2009;113(3):c177-82.
doi: 10.1159/000232599. Epub 2009 Aug 12.

Random spot urine protein/creatinine ratio is unreliable for estimating 24-hour proteinuria in individual systemic lupus erythematosus nephritis patients

Lee A Hebert  1 , Daniel J Birmingham, Ganesh Shidham, Brad Rovin, H N Nagaraja, Chack-Yung Yu
Affiliations
Comparative Study

Random spot urine protein/creatinine ratio is unreliable for estimating 24-hour proteinuria in individual systemic lupus erythematosus nephritis patients

Lee A Hebert et al. Nephron Clin Pract. 2009.

Abstract

Background: Recently the American Rheumatologic Association (ARA) recommended random spot urine protein/creatinine ratio (P/C) to monitor systemic lupus erythematosus (SLE) glomerulonephritis (GN). Shortly afterward, 2 works were published, designated Study 1 and Study 2, which are the only studies to test spot P/C in SLE GN. Here we evaluate Study 1 and Study 2, which came to different conclusions.

Methods: Study 1 compared spot P/C to the P/C of intended 24-hour collections >50% complete, which reliably estimates 24-hour proteinuria. Study 2 compared spot P/C to the protein content of intended 24-hour collections >80% complete. To compare studies, Study 2 data were converted to P/C ratios.

Results: Study 1 and Study 2 were found to be in agreement. Both showed that spot P/C and 24-hour P/C were highly correlated, but only when compared over the entire P/C range (0-8.0) (r = 0.842). Over the P/C range 0.5-3.0 (the most common P/C range encountered in SLE GN), correlation was present, but concordance was poor, rendering random P/C ratio unreliable.

Conclusions: Random spot P/C ratio is unreliable for detecting moderate proteinuria change. For example, random spot P/C would not reliably diagnose British Isles Lupus Assessment Group (BILAG) Category A or B proteinuric flares.

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Figures

Fig. 1.
Fig. 1.
Comparison of Study 1 random spot urine P/C ratios in relationship to the paired actual (measured) 24-hour urine P/C ratios (closed circles), and in relationship to the paired imputed 24-hour urine P/C ratios (open circles). As shown, the variability between random spot urine P/C ratio and measured 24-hour urine P/C ratio is similar to the variability between random spot urine P/C ratio and imputed 24-hour urine P/C ratio. The regression of random spot urine P/C ratio on measured 24-hour urine P/C ratio (solid line) is slope 0.884, intercept 0.156, r2 = 0.553. The regression of random spot urine P/C ratio on imputed 24-hour urine P/C ratio (dotted line) is slope 0.884, intercept 0.290, r2 = 0.546.
Fig. 2.
Fig. 2.
Relationship between 24-hour P/C ratio and the ratio: (spot P/C)/(24-hour P/C) for the cohorts of Study 1 (closed circles) and Study 2 (open circles) with P/C ratios 0.5 to 3.0. These data are shown in relationship to the expected limits of agreement (dotted horizontal lines) between random spot urine P/C ratio and 24-hour urine P/C ratio, if they were equally precise in estimating 24-hour proteinuria. See text for further discussion.
Fig. 3.
Fig. 3.
Relationship between 24-hour P/C ratio and the ratio: (spot P/C)/(24-hour P/C) for the cohorts of Study 1 (closed circles) and Study 2 (open circles) with P/C ratios >3. See text for further discussion. The conventions in figure 3 are the same as those in figure 2.
See this image and copyright information in PMC

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