Objectives: Besides the measurement of IGF-1, GH suppression during OGTT to assess the biochemical status in acromegaly is recommended. However, as a consequence of the development of highly sensitive and specific GH assays a critical re-evaluation of the criteria for the diagnosis and follow-up management of acromegaly is mandatory. The aim of our study was to evaluate the between-method discrepancies in GH determinations by different immunoassays considering further confounders like age, gender, and BMI.
Methods: GH was measured during a 75-g OGTT in 10 controlled and 22 uncontrolled acromegalics (12 men; age 3162 years; BMI 2130 kg/m2) and in 213 apparently healthy subjects (66 men; age 2076 years; BMI 1962 kg/m2) using 3 different assays (DPC Immulite 2000, Nichols and DSL-10-19100) that are calibrated against recommended standard (IS 98/574). Ethical Committee approval was obtained.
Results: There was a strong correlation between all assays (r=0.720.994, P<0.0001). However, the results obtained with DPC were, on average, 2.4-fold higher than those obtained with Nichols and 11-fold higher than those obtained with DSL. GH-nadir in controlled acromegalics was 0.98±0.26 μg/l (DPC) and 0.5±0.15 μg/l (Nichols), whereas in those with an active disease was 7.98±1.7 and 4.5±1.2, respectively. In controls, GH-nadir was 0.13±0.01 μg/l (DPC), 0.06±0.01 μg/l (Nichols) and 0.018±0.004 μg/l (DSL). Both basal and nadir-GH were significantly higher in females than in males (DPC: 2.2±0.28 vs. 0.73±0.15 μg/L and 0.16±0.013 vs. 0.08±0.01 μg/L, P<0.001, respectively). Age, BMI and waist/hip ratio correlated negatively with both basal and nadir-GH (r=−0.2, −0.32 and −0.48, P<0.01). In multiple regression analysis age, BMI and waist/hip ratio were independent predictors for both the basal and the nadir-GH (β-values ranging from −0.2 to −0.3 and −0.14 to −0.3, respectively).
Conclusions: Post-glucose GH-nadir values are assay-, gender-, age- and BMI-specific indicating the need of individual cut-off limits for each assay.