Detection and quantification of beta-2-microglobulin using mass spectrometric immunoassay

The use of mass spectrometric immunoassay (MSIA) in analyzing beta -2-micro globulin (beta (2)m) present in human biological fluids (tears, saliva, pla sma, and urine) is described, Pipettor tips containing porous affinity frit s, derivatized with polyclonal anti-beta (2)m immunoglobulin, mere manufact ured and used to selectively isolate and concentrate beta (2)m from the bio fluids, after which matrix-assisted laser desorption/ionization time-of-fli ght. mass spectrometry was used to detect beta (2)m unambiguously at its ch aracteristic molecular mass. The affinity tips were found rapid to use, req uiring approximately 15 min per analysis, and exhibited low nonspecific bin ding properties that yielded essentially interference-free analyses. The be ta (2)m MSIA was made quantitative by inclusion of an internal standard int o the analysis for signal normalization. The resulting assay had a Linear d ynamic range (R-2 = 0.983) covering a beta (2)m concentration range of 0.01 0-1.0 mg/L with a standard error of approximately 5%. In application, urine samples from healthy individuals were screened and compared with sample fr om an individual suffering from renal infection. Results indicated an appro ximately 30-fold increase in beta (2)m levels in samples taken from the inf ected individual. During the screening, MSIA was able to distinguish betwee n wild-type and glycosylated forms of beta (2)m, which made possible the ac curate quantification of mild-type beta (2)m without interference from glyc osylated versions of the protein. These results demonstrate a new approach to the rapid and accurate detection/quantification of beta (2)m present in biological fluids. (C) 2001 Academic Press.