Improving the urine spot protein/creatinine ratio by the estimated creatinine excretion to predict proteinuria in pediatric kidney transplant recipients.

Background: Since the daily creatinine excretion rate (CER) is directly affected by muscle mass, which varies with age, gender, and body weight, using the spot protein/creatinine ratio (Spot P/Cr) follow-up of proteinuria may not always be accurate. Estimated creatinine excretion rate (eCER) can be calculated from spot urine samples with formulas derived from anthropometric factors. Multiplying Spot P/Cr by eCER gives the estimated protein excretion rate (ePER). We aimed to determine the most applicable equation for predicting daily CER and examine whether ePER values acquired from different equations can anticipate measured 24 h urine protein (m24 h UP) better than Spot P/Cr in pediatric kidney transplant recipients.

Methods: This study enrolled 23 children with kidney transplantation. To estimate m24 h UP, we calculated eCER and ePER values with three formulas adapted to children (Cockcroft-Gault, Ghazali-Barratt, and Hellerstein). To evaluate the accuracy of the methods, Passing-Bablok and Bland-Altman analysis were used.

Results: A statistically significant correlation was found between m24 h UP and Spot P/Cr (p < .001, r = 0.850), and the correlation was enhanced by multiplying the Spot P/Cr by the eCER equations. The average bias of the ePER formulas adjusted by the Cockcroft-Gault, Ghazali-Barratt, and Hellerstein equations were -0.067, 0.031, and 0.064 g/day, respectively, whereas the average bias of Spot P/Cr was -0.270 g/day obtained by the Bland-Altman graphics.

Conclusion: Using equations to estimate eCER may improve the accuracy and reduce the spot urine samples' bias in pediatric kidney transplantation recipients. Further studies in larger populations are needed for ePER reporting to be ready for clinical practice.