These differences account for the discrepancies between growth hormone concentrations measured in a 22K-growth hormonespecific assay versus an assay that measures both the 20K and other non-22K isoforms.10 The clinical use of pegvisomant, a growth hormone analogue that acts as a competitive receptor antagonist and is approved for the treatment of acromegaly, can also result in inaccurate results, and depending on the assay, the result may be high or low.11 This evidence concerns the gene GH1 and acromegaly.