Use of albumin creatinine ratio and urine albumin concentration as a screening test for albuminuria in an Indo-Asian population

Background. Albuminuria (> 30mg/day) based on 24h urine albumin excretion is one of the criteria for chronic kidney disease (CKD) and a predictor of cardiovascular disease (CVD). Differences in urine albumin concentration and creatinine excretion rates between Indo-Asians and other populations may require different threshold values for detection of albuminuria. We compared the use of spot urine albumin concentration and urine albumin to creatinine excretion ratio for detection of albuminuria in this population. Methods. A total of 577 subjects aged >= 40 years, 54% of whom were women, were recruited from the general population in Karachi, Pakistan. Albumin concentration (mg/l) and albumin to creatinine ratio (mg/g of creatinine) were determined in a spot morning urine sample, and albuminuria (30mg/day or greater) measured in a 24h urine collected on the subsequent day. Results. The median (25-75 percentile) of urine albumin excretion was 4.8 (3.6-10.3) mg/day: 5.4 (3.7-12.5) mg/day in men and 4.5 (3.8-8.9) mg/day in women. The overall prevalence (95% CI) of albuminuria was 11.8% (7.2-12.0%): 14.8% in men and 9.2% in women (P=0.04). The areas under the receiver operator characteristic (ROC) curves for urine albumin concentration were 0.86 (0.82-0.90) and 0.88 (0.84-0.92), respectively, in women and men. The areas under the ROC curves for albumin to creatinine ratio were 0.86 (0.82-0.89) and 0.90 (0.86-0.93), respectively, in women and men. For urine albumin concentration, the sensitivity and specificity were 37 and 97%, respectively, in women and 69 and 94%, respectively, in men at the conventionally recommended value of 2mg/dl. The discriminator value of urine albumin concentration identified in the analysis was 0.5mg/dl in women (sensitivity of 87% and specificity of 75%) and 1.7mg/dl in men (sensitivity of 74% and specificity of 93%). For the albumin to creatinine ratio, the sensitivity and specificity were 46 and 95%, respectively, in women and 60 and 97%, respectively, in men at cut-off value of 30mg/g. Conclusion. Both urine albumin concentration and albumin to creatinine ratio are acceptable tests for population screening for albuminuria in Indo-Asians. While sensitivities may be suboptimal, particularly in women, lowering the existing thresholds would compromise specificity. Those who screen positive need evaluation and management of CKD and prevention of CVD.