Can urinary albumin-creatinine ratio be used as a surrogate for protein-creatinine ratio in the diagnosis and management of pediatric steroid sensitive nephrotic syndrome?

BACKGROUND: In pediatric nephrotic syndrome (NS), conventionally, spot urinary protein-creatinine ratio (PCR) is used for diagnosis and to define relapse and remission. This study evaluates whether urine albumin-creatinine ratio (ACR) can reliably predict proteinuria status to manage NS according to existing guidelines, when PCR values are unavailable. METHODS: Children between 1 to 18 years of age with steroid sensitive NS (SSNS) were included. Blood samples for albumin, creatinine, and first or second morning urine samples for albumin, total protein, and creatinine were collected; PCR and ACR were calculated in mg/mg. Correlation between ACR and PCR was assessed using Spearman's rank correlation coefficient and agreement by Bland-Altman analysis. ACR thresholds corresponding to PCR-defined remission and relapse were derived using fivefold internal cross-validation with bootstrap resampling and linear regression modelling. Diagnostic performance was evaluated by sensitivity and specificity using PCR thresholds as the reference standard. RESULTS: In 202 patients (median age 7.4 years, 63% male, normal creatinine for age), ACR and PCR were highly correlated (rs = 0.97), with good agreement on Bland-Altman analysis. Using the internally cross-validated data, PCR values of 2 mg/mg and 0.2 mg/mg yielded median ACR cutoffs of 1.47 to 1.57 for relapse and 0.10 to 0.28 for remission. The associated sensitivities and specificities ranged between 90 to 100% and 91 to 100%, respectively, for relapse. For remission, sensitivities stayed at 100% across all five rounds, whereas specificities varied between 79 and 100%. The recommended averaged ACR thresholds are 1.50 mg/mg (relapse) and 0.19 mg/mg (remission), respectively. CONCLUSIONS: In this study, spot urinary ACR had very strong association and good agreement with PCR in children with SSNS. The ACR cutoffs obtained can be useful in diagnosis and follow-up of SSNS or in evaluating retrospective study data when ACR is available rather than PCR.