RESUMO
Quantification of IGF-I is relevant in both doping control as a biomarker of growth hormone (GH) misuse in sports, and in the clinical field for longitudinal follow-up of patients with disorders related to the GH axis. Currently, better standardization of IGF-I measurements using mass spectrometry is in our best interest as it would enable long-term monitoring of an athletes' IGF-I levels by its addition to the Athlete Biological Passport (ABP). Here, a simplified and rapid top-down LC-HRMS method for quantification of IGF-I in human serum is presented. A ten-minute precipitation-based offline sample preparation is combined with online sample clean-up and separation on a conventional LC, resulting in a total runtime of nine minutes in between injections. The method was validated in the relevant range of 50-1000 ng/mL for the following parameters: linearity, precision, bias, Limit Of Quantification (LOQ), carry-over, selectivity, recovery and ion suppression. As proof of concept, the presented LC-HRMS assay was compared with results from a previous inter-laboratory study on intact IGF-I quantification using four human GH administration samples. It was additionally compared with the IDS-iSYS immunoassay using 47 athlete serum samples, showing good overall agreement with a slight positive bias of 24.2 ng/mL for the LC-HRMS assay at a mean sample concentration of 234 ng/mL. Also, a discrepancy between commercially available IGF-I reference material for the calibration of quantitative assays is discussed. This is of importance if LC-MS assays for IGF-I are to be harmonized.
