The urine albumin-to-creatinine ratio: assessment of its performance in the renal transplant recipient population

Background and objectives: Microalbuminuria predicts graft loss and death in the renal transplant population. Measurement of the urinary albumin-to-creatinine ratio (UACR) is recommended for its detection. There is uncertainty regarding the optimal UACR cutoff values. Few studies have examined the accuracy of UACR in the general population and none have been conducted in renal transplant recipients. The aim of this study is to determine the performance of UACR in the renal transplant population.

Design, setting, participants & measurements: Renal transplant recipients with a daily urinary albumin excretion rate of up to 300 mg accurately carried out a 24-hour urine collection and provided a morning urine sample for the measurement of albuminuria and UACR. The performance measures of UACR for the detection of microalbuminuria (30 to 300 mg/d) were calculated using different cutoffs.

Results: Median albuminuria was 23 mg/d, and median UACR was 17 mg/g. The area under the receiver-operating characteristic curve was 0.94 in men and 0.98 in women. The optimal cutoff was 21 mg/g in men and 24 mg/g in women. In men, the 30-, 17-, and 21-mg/g cutoffs provided a sensitivity of 0.79, 0.89, and 0.87. In women, the 30-, 25-, and 24-mg/g cutoffs provided a sensitivity of 0.90, 0.97, and 1.0.

Conclusions: These data show that in the renal transplant population, lower gender-specific cutoffs should be used for the detection of microalbuminuria than the recommended 30-mg/g cutoff. These data support the need for a reappraisal of the 30-mg/g cutoff for the detection of microalbuminuria.