Received on September 9, 2005
Accepted on December 29, 2005

Endocrinology and Metabolism

Effect of Sex and Assay Method on Serum Concentrations of Growth Hormone in Patients with Acromegaly and in Healthy Controls

¹ Department of Clinical Chemistry, Helsinki University Hospital, Helsinki, Finland
² Department of Internal Medicine, Peijas Hospital, Vantaa, Finland
³ Division of Endocrinology, Department of Medicine, Helsinki University Hospital, Helsinki, Finland
⁴ Department of Internal Medicine, Jorvi Hospital, Espoo, Finland

^* To whom correspondence should be addressed. E-mail: helene.markkanen{at}hus.fi.

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 µg/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), 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). 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 µg/L), however, the difference was 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 µg/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.