Quantitation of Albumin and Creatinine in Urine by MALDI-TOF Mass Spectrometry

Chronic kidney disease or kidney complications resulting from another systematic disorder can impact the organ's blood filtering capability and cause the passage of high molecular weight, blood-born proteins through the kidneys and into the urine. Clinical analyses for blood proteins in urine are performed to assess proper kidney function or to monitor a diagnosed disorder. Serum albumin is a common target in these clinical assays, and the condition of elevated levels in urine is termed albuminuria. Because of normal variability in urine content and volume, multiple measurements are often made in comparison to creatinine levels within the same urine sample and reported as an albumin/ creatinine ratio (ACR). This article describes a novel means for quantifying albumin and creatinine directly from the same urine sample using matrix-assisted laser desorption-ionization time-of-flight-mass spectrometry (MALDI-TOF-MS). The standard addition of albumin and deuterated creatinine into control urine produced a linear and quantitative response (R^sup 2^ = 0.99 and 0.98) and was used to quantify both analytes across their clinically relevant ranges. This MS-based method represents a simple, fast, and attractive alternative to current clinical methods.