Qualitative analysis of hCG variants and glycoforms in urine, using matrix-assisted laser desorption ionization time-of-flight mass spectrometry: A potential companion diagnostic tool to immunoassays in pregnancy and cancer

Human chorionic gonadotropin (hCG) is a very heterogeneous molecule which has been employed as a diagnostic marker in pregnancy for almost a century and to a lesser extent as a biomarker in cancer where it has found particular use in the diagnosis and monitoring of gestational trophoblastic disease and testicular cancer. The mass of hCG is often reported as around 36kDa, in reality the mass range of the intact holo-hormone ranges between 34 and 40kDa. As such, the term hCG is a collective term encompassing a range of heterogeneous molecules with both subtle and more extensive peptide and oligosaccharide variation. The variation in the size and structure of hCG has been shown to be indicative of different stages in pregnancy as well as associating with certain cancer types and other disorders, and we question whether a simple immunoassay is sufficient to discriminate when quantitative methods may be more helpful. MALDI-TOF MS has great potential in standardizing a qualitative approach to documenting hCG molecular variation which has been challenging using immunoassays. MALDI can easily assign each hCG species to a specific mass range which would allow a qualitative reference to each standard sample preparation and thus guide selection for international standards for different applications. Therefore, direct analysis of urine by MALDI, in combination with quantitative data, which is now also possible by MALDI as well as traditional immunoassays, could lead to a better-informed diagnosis and management of pregnancy and also in cancers where hCG is produced.