Effect of sex and assay method on serum concentrations of growth hormone in patients with acromegaly and in healthy controls

Background: Diagnosis and follow-up of acromegaly is based on measurements of serum growth hormone (GH) concentrations during an oral glucose tolerance test (OGTT). A nadir value <1 mu g/L is commonly used to define a normal response, but some authors suggest lower cutoff values. Methods: To compare the results and subsequent patient classification obtained with 3 GH assays, we obtained basal serum samples from 78 apparently healthy adult controls (43 women and 35 men; median age, 32.5 years) and from 71 treated (44 women and 27 men; median age, 55.2 years) and 7 untreated acromegaly patients (4 women and 3 men; median age, 54.6 years), and OGTT was performed on all patients and on 72 of the 78 controls. GH was determined by 2 immunometric assays-a double monoclonal (AutoDELFIA; Wallac) and a monopolyclonal (Immulite 2000; DPC) assay-and in a limited set of samples by an RIA (Spectria RIA; Orion). Results: There was a strong correlation (r=0.995; P<0.001) between the 2 immunometric methods, but the results obtained with the Immulite 2000 were, on average, 1.4-fold higher than those obtained with the AutoDELFIA. At concentrations around the cutoff (1 mu g/L), however, the difference was similar to 2-fold. Overall, the Orion RIA method also showed a good correlation (r=0.951-0.959) with the other methods, but it did not measure concentrations <2 mu g/L. Women had higher basal and OGTT nadir GH concentrations than men. Conclusion: Reference intervals should be determined separately for each method, and the need for establishing sex-specific reference values should be investigated. (C) 2006 American Association for Clinical Chemistry.