Applications of Top‐Down Protein Analysis in Clinical Diagnostics

This review evaluates the applications of top-down mass spectrometry (TDMS) and intact mass measurement of proteins in clinical laboratories. Both methods involve the measurement of intact proteins in a mass spectrometer without the use of enzymatic or chemical digestion to convert the protein into smaller peptides, and TDMS includes fragmentation of selected proteins. These analytical techniques offer significant advantages in the ability to distinguish pathologically relevant proteoforms from nonpathologic proteoforms compared to alternative immunoassays, and the potential to reduce laboratory turnaround times relative to proteolysis-aided approaches. As a result, TDMS and intact MS have already penetrated the clinical laboratory for many tests that require high analytical specificity and high throughput. This article describes several examples for which TDMS and intact MS methods are currently used in clinical diagnostics, including hemoglobinopathy determination, myeloma isotyping, transferrin glycosylation measurement, and the quantitation of endogenous and exogenous hormones (e.g., insulin and therapeutic variants), while examining new TDMS-based clinical tests which may soon be offered in clinical laboratories. The overall outlook of future TDMS clinical testing is also discussed.