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Spot urine protein/creatinine ratio (PCR) is often used clinically to estimate 24-hour (24-h) proteinuria. However, urine PCR shows considerable hour to hour variability.1 ,2 In lupus nephritis (LN), spot PCR reveals this variability, while longer timed collections conceal it.3–5 Spot PCR performs well in cohort studies, where its variability is mitigated by averaging the data.6 However, spot PCR variability becomes a liability for individual patient management. This work is the first to compare spot PCR variability in LN and chronic kidney disease (CKD).
For LN, we used the published works (N=3, 165 patients) that documented the completeness (creatinine content) of the 24-h urine collections3–5 (LN studies A, B, and C, respectively). For CKD, we used a standard CKD cohort (ramipril efficacy in nephropathy (REIN) Trial, 98 patients), which documented completeness of the collections.6 Almost all spot PCRs were from morning collections.
As shown in the calibration …