Comparative phenotypic analyses of human plasma and urinary retinol binding protein using mass spectrometric immunoassay.

Mass spectrometric immunoassay (MSIA) is a proteomics technology that combines the selectivity of affinity capture with the sensitivity and resolution of mass spectrometric detection. This unique approach allows for intact protein identification therefore is readily capable of discriminating between protein variants, i.e., mutations, posttranslational modifications, and truncations. In this work, MSIA is used in the comparative analyses of retinol binding protein (RBP) from the plasma and urine of a small study population. Detailed RBP profiles were obtained from both biological fluids, resulting in the identification of several catabolic RBP products (present in urine) that have not been previously reported. In addition, comparative analysis of urine samples taken from healthy and renally impaired individuals revealed different breakdown profiles. These results illustrate the use of MSIA for the rapid, sensitive, and accurate profiling of RBP both within and between individuals.