Abstract des Autors

Anti-doping laboratories routinely use immunoassays to measure urinary concentrations of human chorionic gonadotropin (hCG). To minimize immunoassay differences and false positive screen results from inactive isoforms (free β-subunit (hCGβ), β-subunit core fragment (hCGβcf)) laboratories now use intact hCG instead of total hCG immunoassays to measure hCG. To determine the distribution of hCG isoforms in urine, we determined the concentrations of intact hCG, hCGβ, and hCGβcf in male urine samples based on immunoassay total hCG concentrations using a sequential immunoextraction and a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. hCG was isolated using antibody-conjugated magnetic beads and unique tryptic peptides were quantified by LC-MS/MS. Negative samples with detectable but low total hCG concentrations (1.2–3.5 pmol/L) had intact and hCGβ concentrations <1.2 pmol/L, and hCGβcf concentrations <2.3 pmol/L by LC-MS/MS. Urine samples from an athlete receiving hCG had intact hCG concentrations ranging from 18.8 to 57.6 pmol/L, hCGβ concentrations <0.7 pmol/L, and hCGβcf concentrations ranging from 94 to 243% of the intact hCG concentration. In 27 atypical samples with total hCG concentrations ranging from 16.7 to 412.7 pmol/L with intact hCG <2.7 pmol/L by immunoassay, all samples had intact hCG concentrations <3.8 pmol/L and hCGβ concentrations <6.2 pmol/L by LC-MS/MS. hCGβcf concentrations by LC-MS/MS varied widely and ranged from 1.03 to 21.9 pmol/L. In summary, total hCG immunoassays significantly overestimate hCG concentrations and can produce false positive results. Although the intact hCG immunoassay slightly overestimates hCG concentrations compared to LC-MS/MS, it can distinguish between cases of hCG use and atypical cases with elevated total hCG concentrations.