Automated 22-kD Growth Hormone–Specific Assay without Interference from Pegvisomant

Abstract

BACKGROUND:Large variability exists among different growth hormone (GH) assays owing to differences in calibration, antibody specificity, isoform recognition, and interference from GH binding protein (GHBP). The GH receptor antagonist Pegvisomant presents a new challenge because Pegvisomant interferes with many GH assays. A recent consensus conference established criteria for standardization and evaluation of GH assays. Following consensus recommendations, we developed a new GH assay on an automated analyzer (IDS-iSYS, Immunodiagnostic Systems). METHODS:A monoclonal antibody not cross-reacting with Pegvisomant was combined with a monoclonal antibody specific for 22-kD GH. Isoform specificity and interference from GHBP was tested and compared to that seen in 2 existing automated GH assays (Siemens Immulite, Diasorin Liaison). We also compared GH concentrations measured by the 3 assays for healthy volunteers and patients with acromegaly receiving different treatments. Using the iSYS assay, we also established nadir GH values during oral glucose load and analyzed changes in endogenous GH during Pegvisomant treatment. RESULTS:Analytical and functional sensitivities were 0.01 g/L and 0.04 g/L, with a dynamic range from 0.04 to 100 g/L. Intraassay CVs were 2%-4%, whereas interassay CVs were 5%-7% at GH concentrations between 1.7 and 27.5 g/L. The assay was specific for 22-kD GH and not affected by GHBP. The presence of Pegvisomant, which leads to a negative bias on the Immulite and dramatic overestimation of GH on the Liaison, had no impact on the iSYS GH assay. CONCLUSIONS:The new assay fulfils recent consensus recommendations and presents a useful new tool for reliable measurement of GH.

MANAGEMENT OF ENDOCRINE DISEASE: Acromegaly and pregnancy: a contemporary review

“…GH isoforms cross-react in most immunoassays, but specific assays for 22K-GH, 20K-GH, for both, and for GH-V have been developed (8,19,28).…”

“…As a result, single-center case series (2) and multicenter retrospective (3,4) and prospective studies (5) on pregnancy in patients with acromegaly that have been published in recent years have added new and relevant information to the preexisting literature (6,7). Moreover, the development of GH immunoassays with selective specificities (8,9) and the increasing knowledge of the expression of the various genes (10,11) have allowed substantial improvement in our understanding of the changes in the somatotrophic axis that take place during pregnancy.…”

Pitfalls of Insulin-like Growth Factor-I and Growth Hormone Assays

“…Literature only reports few GH assays that are free of pegvisomant interference, whereas most investigated assays greatly overestimate or underestimate GH levels in presence of pegvisomant. 26 "Go permissive or go specific?" is a traditional question when designing an assay for GH.…”

Exploiting Nanobodies in the Detection and Quantification of Human Growth Hormone via Phage-Sandwich Enzyme-Linked Immunosorbent Assay

“…GH immunoassays vary significantly because of the differences in calibration, isoform recognition, interference with GH-binding proteins, and antibody specificity (45). There are several isoforms of GH circulating in blood together with the binding proteins (growth hormone-binding protein) making the measurement of GH a complicated task.…”