Tracking growth hormone abuse in sport: a comparison of distinct isoform-based assays.

Detecting recombinant human growth hormone (rhGH) abuse in sport remains one of the major challenges in doping control. We have compared two different approaches to detect the hGH (human growth hormone) abuse. The first measures the concentrations of the 22 kDa hGH isoform (rec assay) and pituitary derived isoforms (pit assay) and a ratio rec/pit is obtained. The second measures the concentrations of 22 and 20 kDa hGH isoforms and also a ratio 22/20 kDa is derived. Using a single set (nine healthy male subjects, 7 days, 0.026 mg/kg/day of rhGH, 2 week wash out period) both approaches were compared. To quantify the agreement between the immunoassays, B.A. (Bland-Altman) analysis and P.r. (Pearson correlation) were used. To fully understand the assay readings, all relevant antibodies were characterised by surface plasmon resonance (SPR). In either approach the ratio numerator produces similar results and the denominator determines both signal-amplitude and time-frame of possible application. The rec vs pit approach displays a higher distinctive capacity to detect hGH abuse but the complex binding properties of the capture antibodies make it very difficult to evaluate the precise contributions of the individual hGH variants to the assay result. In the 22 vs 20 approach, the 20 kDa hGH concentration measures determine its applicability. Both approaches are based on a different principle, should be preferably applied within 24 h after rhGH administration, and are perfectly comparable given the results obtained. The reduced time frame of application indicates that their principle application should be preferably in an out-of-competition setting.