One of the main influencing factors for hGH immunoassays is the presence of GHBP (5).
Impact of GHBP interference on estimates of GH and GH pharmacokinetics.
The previously mentioned experiments indicated that AN98 specifically reacted with porcine GHBP
. Next, we further identified the reaction of A98 with pGHR (full-length pGHR) expressed on target cells.
Recombinant GHBP interference was tested more extensively in 4 samples containing low, medium, and high endogenous GH concentrations.
Cross-reactivity of 20-kD GH and interference from Pegvisomant and GHBP were also investigated in the Siemens Immulite and Diasorin Liaison.
Information available in a manufacturer's assay literature should specify the following: the identity of the reference preparation; calibration information, including traceability to the international reference standard; assay cross-reactivity with 20-kDa GH, placental GH, and therapeutic GH analogs; GHBP interference; limits of quantification; assay performance at the upper and lower limits of the normative reference intervals; and QC data.
 Nonstandard abbreviations: GH, growth hormone; IGF-I, insulin-like growth factor I; GHBP, GH-binding protein; IGFBP, IGF-binding protein; IS, international standard; NIBSC, National Institute of Biological Standards and Control.
Plasma GHBP and urine insulin-like growth factor (IGF)-1 have also been evaluated in a group of subjects (20 males and 20 females for GHBP, and 30 males for IGF-1).
GH (urinary and plasma) and GHBP values (MBC and B/F) of the population studied.
 Nonstandard abbreviations: GHD, growth hormone deficiency; GH, growth hormone; PD, pyridostigmine; GHRH, growth-hormone-releasing hormone; and GHBP
, growth-hormone-binding protein.
In addition, the importance of two other suspected sources of variability in GH measurements (i.e., GH isoforms and GHBP) was evaluated.
GHBP (generously donated by Genentech, South San Francisco, CA) at 16, 31, 63,125, 250, and 500 pmol/L was added to serum samples, and GH concentrations were measured by the p-IRMA and trIFMA.