The urine protein to creatinine ratio (P/C) as a predictor of 24-hour urine protein excretion in renal transplant patients.

Abstract

The purpose of this study was to examine the utility of the random urine protein to creatinine ratio (P/C) in evaluation and longitudinal management of proteinuria in adult renal transplant recipients with or without overt nephropathy in an outpatient clinic. A total of 289 adult renal transplant recipients provided 24-hr urine collections for total protein and creatinine, followed by a random urine for protein and creatinine. For longitudinal analysis, 192 of these patients provided two 24-hr urine collections with concomitant random urine specimens separated on average by 6.8 months. As well, 134 patients provided a total of 851 multiple-paired spot and 24-hr urine samples (range 2 to 12) over a 2-year period. The log random urine P/C ratio correlated significantly to the log 24 UP (r=0.749, P<0.0001) with or without nephrotic range proteinuria. High sensitivity (74.4-90%) and specificity values (93-98%) were found for estimating proteinuria from 0.5 to 2 g/day. However, the precision of estimation decreased as the level of urinary protein excretion increased to >3 g/day. The positive predictive value decreased as proteinuria became >3 g/day, perhaps because of the low prevalence of patients with high level proteinuria in our sample. The direction of change in P/C ratio longitudinally was accompanied by a similar direction of change in 24 UP, which was highly significant (r=0.7555, P<0.0001). We conclude that the urine P/C ratio is a useful and convenient screening and longitudinal test for proteinuria.