3-4
Measurement of albuminuria in screening forof chronic kidney disease
Fang Wang1, Luxia Zhang1, Puhong Zhang2, Haiyan Wang1
1Renal Division, Department of Medicine, Peking University First Hospital, Beijing, China
2Beijing Center for Disease Control and Prevention

Background:
Albuminuria was a marker widely used in screening of chronic kidney disease(CKD). The Kidney Disease: Improving Global Outcomes (KDIGO) initiative recommends repetitive measurement of albuminuria to confirm chronic kidney damage. The aim of this study was to assess the necessity of repetitive measurement of microalbuminuria. The accuracy of urinary albumin-to-creatinine ratio (ACR) and the Micral-Test II test strip in random urine specimens for microalbuminuria screening in general population were also evaluated.

Methods:
Urinary ACR of random spot urine specimens was measured among a random selected sample of 659 participants from Beijing citizens. Five months later, two random spot urine samples and 24h urine sample in the same day were collected from these participants. We compared ACR and Micral-Test II test strip results with albumin measured in the 24h urine sample.

Results:
The area under the ROC curves for ACR of random urine (0.927ｱ0.011) was better than Micral-Test II test strip (0.835+0.018). The sensitivity and specificity for a cutoff value of 30mg/g were 79.1% and 90.9%, respectively. For a cutoff point of 20 mg/l as for Micral-Test II test strip , sensitivity and specificity were 90.3% and 41.1%. Kappa value of agreement measurement between ACR of random spot urine in the same day was 0.72 (P=0.000). For individuals with albumiuria in the first random urine, 89% were still positive in the second random spot urine in the same day. But among individuals with microalbuminuria at the first screening, only 52.7% had microalbuminuria or macroalbuminuria at the second visit 5 months later. Concerning the participants with normoalbuminuria at the first visit, 90% still had normoalbuminuria at the second time. Eighty-three percent individuals with macroalbuminuria had macroalbuminuria or microalbuminuria at the second visit. Kappa value of agreement test of albuminuria between two different days was 0.46 (P=0.000). The repetitiveness of albuminuria was progressively greater at lower kidney function (48.7% in stage 1, 62.8% in stage 2, 78.26% in stage 3 , 83.3% in stage 4 ). By repeated micro albuminuria measurement, the rate of albuminuria reduced by 43.9% in our study population.

Conclusions:
Repeated microalbuminuria measurement over a more than 3 months interval was necessary to confirm persistent albuminuria. Considering of the convenience and diagnostic accuracy, we recommend use of the Micral-Test II test strip for the first visit,and urinary albumin-to-creatinine ratio for the second visit to confirm albuminuria in screening forof chronic kidney disease in the general population.