ß2-microglobulin measurement with dried urine spots for congenital anomalies of the kidney and urinary tract screening in 3-year-old children.

BACKGROUND: Screening using dipstick urinalysis has long been performed in 3-year-old children; however, it is ineffective in detecting congenital anomalies of the kidney and urinary tract (CAKUT). Measurement of the urinary ß2-microglobulin (ß2MG)/creatinine (Cr) ratio may be more effective for this purpose. Analysis of dried urine spots (DUS) on filter paper is suitable for mass screening since operational costs are low and samples are easy to collect and transport. We examined the accuracy of measuring the urinary ß2MG/Cr ratio in DUS on filter paper. METHODS: We collected 2,623 urine samples from 3-year-old children. ß2MG and Cr levels were measured in DUS on filter paper. We examined the correlation between the ß2MG/Cr ratios measured in DUS and using the conventional method in 640 samples using the coefficient of determination test. Children with high ß2MG/Cr ratios (>0.6 µg/mg Cr) in DUS samples were further examined to establish a definitive diagnosis. RESULTS: There was strong correlation between the two methods for determination of ß2MG levels (r2 = 0.68; P < 0.001) and ß2MG/Cr ratios (r2 = 0.69; P < 0.001). Of the 2,623 children, 38 (1.45%) had ß2MG/Cr ratios >0.6. Thirty-five children were subsequently examined, resulting in findings of renal hypodysplasia (n = 2, 0.08%), horseshoe kidney (n = 1, 0.04%), renal tubular dysfunction with hepatoblastoma (n = 1, 0.04%), data abnormality (high urine ß2MG level, n = 6, 0.23%; high serum Cr level, n = 1, 0.04%), and normal values (n = 24, 0.91%). CONCLUSIONS: We evaluated a practical method for measuring ß2MG/Cr ratios in DUS as a screening method to detect CAKUT in 3-year-old children.