Measurement of microalbuminuria using protein chip electrophoresis

Microalbuminuria reflects the progression of nephropathy and cardiovascular disease in diabetic and hypertensive patients. Most commercially available tests currently used to measure microalbuminuria are immunoassays. We developed a microfluidics-based assay using the P200 protein chip (Caliper Life Sciences, Mountain View, CA, and Agilent Technologies, Santa Clara, CA) and 2100 Bioanalyzer (Agilent Technologies) to detect microalbuminuria. The method integrates and automates the electrophoretic separation and fluorescent detection of proteins from 14 to 200 kd. The assay was linear up to 750 mg/L and demonstrated good sensitivity with a lower detection limit of 7.5 mg/L. Intrachip and interchip coefficients of variation ranged from 0% to 4% and 4.9% to 13.5%, respectively. When albumin was measured by chip and immunoturbidimetry in diabetic urine samples, the chip consistently showed higher albumin concentrations. The discrepancy may be due to the chip's ability to detect immunounreactive albumin. Overall, this simple, cost-effective assay offers a sensitive and accurate measurement of microalbuminuria that can be easily implemented in a clinical laboratory.