Isotopic differences in human growth hormone preparations.

The 13C/12C isotope ratios have been measured for human pituitary growth hormone and three commercial growth hormone products in an attempt to differentiate endogenous versus exogenous origin. This might be a strategy to detect doping, as has recently been recognized for testosterone. While all preparations are statistically different from each other, we find that only Humatrope from Lilly has a carbon isotope ratio that is markedly different from those of human growth hormone or Genentech's Nutropin and Protropin. The low renal clearance of growth hormone reduces the applicability of this concept.