Determination of Urea in Human Serum and Epithelial Lining Fluid Using LCMS; Benchmarking to a Traditional Diagnostic Colorimetric Kit

Difficulties are common in estimating the actual concentration of recovered pharmaceutical entities in epithelial lining fluid (ELF) following a bronchoalveolar lavage (BAL) procedure due to uncertainty around existing ELF volume. Therefore, an endogenous biomarker (urea) is typically used to determine the volume of recovered ELF (relative to volume of saline instilled), after a BAL procedure. The most widely used method for urea determination in clinical laboratories utilizes a colorimetric assay kit such as QuantiChrom™, which is designed to measure urea directly in a variety of biological matrices without any sample pretreatment. Current FDA guidance requiring in-lab validation of diagnostic kit-based assays, along with a possible 40% positive bias when analyzing serum samples using a kit, make a selective and accurate LC-MS assay essential and cost-effective to explore.