How useful is IGF-I in adults with GH deficiency?
S DeSilva, A Soni, C Tsametis, A Marland, N Karavitaki, S Suliman, HE Turner & JAH Wass
INTRODUCTION: Although IGF-I is considered to reflect the daily GH secretion, its value in establishing the diagnosis of adult growth hormone deficiency (GHD) and in predicting the presence of further anterior pituitary deficits has not been elucidated in a large series.
AIM: To evaluate the diagnostic utility of a subnormal IGF-I in patients with GHD and to investigate whether a low IGF-I is associated with the presence of further anterior pituitary deficits.
PATIENTS AND METHODS: The records of 97 patients (53 females, median age 50 years [range 17-78]) who presented to our Department with GHD were reviewed. The diagnosis was established by peak GH<10 mU/L in an ITT (n=46 [27 females], median age 47 [17-72], BMI 29±4.9) and/or a Glucagon test (n=52 [26 females], median age 49 [19-78], BMI 29.6±5.2). All subjects were well nourished, on optimal hormone replacement therapy (if necessary) and with normal liver and renal function at the time of IGF-I measurement.
RESULTS: Subnormal IGF-I was found in 50% of the patients in the ITT group and 38.5% in the Glucagon group. BMI did not differ between patients with normal or subnormal IGF-I (ITT:28.4±5.3 vs 29.5±4.6, Glucagon test:29.9±3.9 vs 29.1±6.7). IGF-I values and peak GH levels were significantly correlated in the ITT group only (r=0.466, p=0.003). 60% of the patients with low IGF-I had complete hypopituitarism, 26% 2 more deficits and 5% one more. The corresponding values for subjects with normal IGF-I were 44.6&, 21.4% and 25%, respectively. The number of patients with low IGF-I and 2 or more pituitary deficits was significantly higher than the number of patients with normal IGF-I and 2 or more deficits (p<0.01).
CONCLUSIONS: IGF-I levels do not reflect the GH secretory reserve in adults with GHD. A subnormal IGF-I in these patients is likely to be associated with multiple hormonal deficits.