Simultaneous quantitation of urinary albumin and creatinine for rapid clinical albuminuria diagnostics using high-throughput paper spray mass spectrometry

Abstract

Albuminuria is a clinical condition associated with poor kidney function, diagnosed by determining the ratio of albumin to creatinine concentrations in patient urine samples. We present a high-throughput paper spray mass spectrometry (PS-MS) method for simultaneous quantitation of urinary albumin and creatinine for potential diagnosis of albuminuria. Minimal (urine dilution) or no sample preparation is required. The analytical performance of the method was evaluated, achieving linear calibration curves (R² > 0.99) with little inter-day variability in the slope (N = 5 days), exhibiting coefficient of variation (CV) of 8% and 3% for albumin and creatinine, respectively. LOD and LOQ for albumin were 2.1 and 7.0 mg L⁻¹, and for creatinine were 0.01 and 0.03 mmol L⁻¹, respectively. Intra- and inter-day (N = 5) precisions (%CV) and accuracies (%bias) were <10% and ±11%, respectively, for both analytes. The method was applied to determine albumin-to-creatinine ratios in anonymous human patient urine samples (N = 56), and a correlation of R² = 0.9744 was achieved between the PS-MS results and validated clinical method results. This work demonstrates the utility of PS-MS to simultaneously quantify a large (albumin) and a small (creatinine) molecule directly in patient urine samples, and its potential as a tool for clinical albuminuria diagnostics.