GH Doping Detection

Detecting injected growth hormone is hard because the recombinant molecule is identical to the dominant natural one, so mass or immunoreactivity alone proves nothing. The isoform differential test exploits the fact that the pituitary secretes a mixture, with the 22 kDa form predominating but other variants always present, whereas recombinant somatropin is pure 22 kDa. Two immunoassays are run, one recognising the 22 kDa form and one the wider pituitary mixture, and an elevated ratio between them indicates that exogenous hormone has displaced endogenous secretion.

That ratio normalises quickly, giving a detection window measured in tens of hours after the last injection. The biomarker approach, developed as the GH-2000 project and introduced in international competition around the 2012 Games, measures IGF-1 and the N-terminal propeptide of type III procollagen, extending the window to roughly one to two weeks because those markers respond slowly.

For interpreting a result, the asymmetry matters: a positive is strong, a negative is weak. Given the windows involved, a clean sample says little about use weeks earlier, which is the argument for out-of-competition testing and for the longitudinal reasoning behind the athlete biological passport. The biomarker score also needs context, because P-III-NP is a collagen turnover marker that rises with soft-tissue injury, fracture and heavy training.

The claim that growth hormone is undetectable is a decade out of date, but the more consequential misunderstanding is narrower. Athletes routinely assume only recombinant hormone is prohibited, when section S2 of the WADA Prohibited List covers releasing factors as a class, including GHRH analogues and the growth hormone releasing peptides. Those are sanctionable in their own right, and the biomarker test does not care which route raised IGF-1.