The effect of body mass index on the diagnosis of GH deficiency in patients at risk due to a pituitary insult.

Objectives: Diminished GH response to stimulation has been demonstrated in obesity, leading to erroneous diagnosis of GH deficiency. The aim of this study was to evaluate the influence of body mass index (BMI) on GH responsiveness in patients at risk for pituitary function deficits.

Methods: A total of 59 healthy subjects and 75 patients with a pituitary insult underwent insulin tolerance test or pyridostigmine+GHRH test in order to assess GH secretory reserve. Normal subjects and patients were classified as normal weight (BMI <24.9 kg/m(2)), overweight (BMI 25-29.9 kg/m(2)), and obese (BMI >30 kg/m(2)).

Results: All normal individuals with BMI <24.9 kg/m(2) demonstrated adequate GH responses, while three of the 21 overweight (14.3%) and nine of the 28 obese subjects (32.1%) did not respond to GH stimulation. Among patients, four of 14 (28.6%) with BMI <24.9 kg/m(2), 18 of 22 (81.8%) who were overweight, and 28 of 39 (71.7%) who were obese did not respond to GH stimulation. Of the 46 nonresponder patients with increased BMI, nine (19.6%) had normal insulin-like growth factor 1 (IGF1) values and no other pituitary hormone deficits, raising questions about the accuracy of somatotroph function assessment, while all nonresponders with BMI <24.9 kg/m(2) had low IGF1 values and panhypopituitarism.

Conclusions: Our results indicate that BMI >25 kg/m(2) has a negative effect on GH response not only in normal healthy subjects but also in patients at risk for pituitary function deficit as well. Parameters such as IGF1 levels and anterior pituitary deficits should be taken into account to accurately assess GH status in these patients.