Background/Purpose: Twenty-four hour proteinuria (24hp) has been the gold standard for the screening and follow up of glomerular disease. The use of protein/creatinin urinary index (PCI) in a spot urine sample, has been proposed as an alternative to 24hp due to its low cost and simple recollection of the sample. This method has been validated in patients with diabetic and non-diabetic nephropathy, with less data in patients with Systemic Lupus Erythematosus (SLE). The aim of this study was to measure the correlation and concordance between this two methods in patients with SLE

Methods: Paired samples of 24hp (in grams in 24 hours) and PCI (first urine sample, expressed in mg/g) in SLE diagnosed patients with or without lupus nephropathy, collected between June 2015 and May 2018, in Señor del Milagro’s Hospital at Rheumatology Unit were included for the analysis. PCI value is 1000 times higher than 24hp. Walser’s index (WI) which evaluates the quality of the collected sample on 24hp, calculated with estimated and measured urine creatinine, age and weight was performed. A WI between 0.75 to 1.25 reflects well collected 24hp. Qualitative data was expressed in frequency and percentages, quantitative data in medians and interquartile range (IQR) or media and standard deviation (SD) depending on its distribution. Spearman test was performed to assess correlation between 24hp ande PCI was. In order to analyze concordance between PCI and 24hp, the PCI was multiplied by 1000. Interclass Concordance Coefficient (ICC), with (crohnbach’s alpha) was calculated. Receiver operating curves (ROC) with under the curve area (UCA) were calculated for 24hp values of ≥ 0.3, 0.5, 1 and 3.5 grams per 24 hours, in order to calculate IPC cutpoints. A p value < 0.05 was considered significative.

Results: 68 patients, 60 (88.2) female, median age 33 years (IQR: 27-48), and 187 paired urine samples were included. Spearman’s correlation between the 2 methods was 0.84. ICC was > 0.9 for the whole sample, 0.92 when WI was acceptable (n=88) and only dropped to 0.88 in the context of “non-acceptable” WI (n=99). Considering only acceptable WI samples, ROC curves showed cutpoints of 333 mg/g, 407 mg/g, 984 mg/g and 3013 mg/g had good sensitivity and specificity (S 77, Sp 87 or higher) to predict 24hp of 0.3 g, 0.5 g, 1 g and 3.5 g.

Conclusion: In this sample of SLE patients, 24ph and PCI had a good ICC and correlation, considering an acceptable WI. The use of PCI could replace 24ph in the assessment of glomerular disease in SLE patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/protein-creatinin-urinary-index-has-concordance-with-24-hour-urinary-proteinuria-in-patients-with-systemic-lupus-erythematosus/