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. 2024 Nov 21;25(1):418.
doi: 10.1186/s12882-024-03804-7.

The urine protein/creatinine ratio as a reliable indicator of 24-h urine protein excretion across different levels of renal function and proteinuria: the TUNARI prospective study

Gabriel Brayan Gutiérrez-Peredo  1   2   3   4 , Iris Montaño-Castellón  5   6   7 , Andrea Jimena Gutiérrez-Peredo  5   6   8 , Marcelo Barreto Lopes  5   6   9   10 , Fernanda Pinheiro Martin Tapioca  11 , Maria Gabriela Motta Guimaraes  11 , Sony Montaño-Castellón  12 , Sammara Azevedo Guedes  11 , Fernanda Pita Mendes da Costa  11 , Ricardo José Costa Mattoso  11 , José César Batista Oliveira Filho  5 , Keith C Norris  13 , Antonio Raimundo Pinto de Almeida  5   6   14 , Antonio Alberto Lopes  5   6   10   14
Affiliations

The urine protein/creatinine ratio as a reliable indicator of 24-h urine protein excretion across different levels of renal function and proteinuria: the TUNARI prospective study

Gabriel Brayan Gutiérrez-Peredo et al. BMC Nephrol. .

Abstract

Background: The 24-h urine protein (24-hUP) excretion is the gold standard for evaluating proteinuria. This study aimed to evaluate the diagnostic efficacy of protein/creatinine ratio (PCR) for estimating 24-hUP at various levels of renal function and proteinuria levels.

Methods: A cross-sectional study was conducted between December 2021 and December 2023 in Salvador, Bahia-Brazil, as an extension of previously published data from the TUNARI study. The study included 217 samples from 152 patients with various levels of renal function and proteinuria. PCR in isolated samples and 24-hUP were determined conventionally within a 24-h timeframe. Patients were classified into three groups according to the level of renal function (Group 1 = 10 to < 30 mL/min, Group 2 = 30-60 mL/min, and Group 3 = > 60 mL/min) and level of proteinuria (< 0.3 g/day, 0.3-3.5 g/day, and > 3.5 g/day). The data were analyzed using the Spearman correlation (rs), coefficient of determination (r2), Bland-Altman plots and receiver operating characteristic (ROC) curve. Likelihood ratios, positive (LR +), and negative (LR-) were derived from the sensitivity and specificity of PCR.

Results: Mean age was 41.5 ± 15.7 years, 61.8% were women, 36.8% Black and 52% Mixed-race. Glomerulopathies constituted 80.3%; 46.1% with lupus nephritis. Of the total urine samples, we observed a high correlation between PCR in the total sample of 24-hUP sample (rs = 0.86, p < 0.001) across different levels of renal function. However, agreement between PCR and 24-hUP was reduced at higher levels of proteinuria. The ROC analysis showed an AUC of 0.95 (95% CI = 0.92, 0.98), sensitivity of 91% and specificity of 86.5% (LR + 6.7; LR- 0.1), with an optimal cut-off of 0.77. These results were similar across renal function levels. Proteinuria ≤ 0.3 g/day showed a high sensitivity of 83.3% and specificity of 90%, with an area under (AUC) of 0.85 (95% CI = 0.71; 0.94). In the 24-hUP range > 0.3-3.5 g/day, the sensitivity was 64.1%, the specificity was 84.6%, and the AUC was 0.76 (95% CI = 0.67; 0.84), PCR detected all cases > 3.5 g/day.

Conclusions: PCR is a suitable measure to be used as an indicator of 24-hUP at different levels of renal function, but may have limitations at higher levels of proteinuria. Analysis of PCR by proteinuria level found that agreement as well as sensitivity decreases at higher levels, but it maintains good specificity and is able to identify nephrotic range proteinuria.

Keywords: 24-h urine protein; Nephrology; Proteinuria creatinine ratio; Renal function.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: The Research Ethics Committee of HUPES at the Federal University of Bahia approved the study protocol, with Certificate of Presentation of Ethical Appreciation (CAAE): 64362522.7.0000.0049 and case number 5.909.208. All patients gave their informed consent to participate. The present investigation was carried out in accordance with the Declaration of Helsinki of the World Medical Association. Consent for publication: This study has the informed consent form duly applied and signed by the participants in accordance with the ethical standards for the publication of their clinical and/or imaging data. This study included obtaining and signing informed consent from participants, in compliance with ethical standards for the publication of their clinical data and images. The anonymity and confidentiality of the information provided was strictly guaranteed. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Flow diagram
Fig. 2
Fig. 2
A Total scatter plot of the protein/creatine ratio (PCR) and 24-h urine protein (24-hUP). B Bland–Altman graph in the evaluation of the concordance between the PCR and the 24-hUP. C Analysis of the receiver operator characteristic (ROC) curve (sensitivity and specificity) between the PCR with 24-hUP
Fig. 3
Fig. 3
Scatter plot of the protein/creatine ratio (PCR) and 24-h urine protein (24-hUP) by three levels of renal function. A Group 1 = 10 to < 30 mL/min. B Group 2 = 30–60 mL/min. C Group 3 = > 60 mL/min
Fig. 4
Fig. 4
Bland–Altman graph according to renal function. A Group 1 = 10 to < 30 mL/min. B Group 2 = 30–60 mL/min. C Group 3 = > 60 mL/min
Fig. 5
Fig. 5
Analysis of the receiver operator characteristic (ROC) curve (sensitivity and specificity) between the protein/creatine ratio (PCR) sample with 24-h urine protein (24-hUP), according to three levels of renal function. A Group 1 = 10 to < 30 mL/min. B Group 2 = 30–60 mL/min. C Group 3 = > 60 mL/min
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