Assessment of disease activity in acromegaly by means of a single blood sample: comparison of the 120th minute postglucose value with spontaneous GH secretion and with the IGF system

OBJECTIVE It has been suggested that the threshold of 1 mug/l of GH nadir after glucose load for definition of controlled acromegalic disease proposed in the 2000 consensus statement should be lowered to 0.30. We evaluated these two cut-off values in comparison with IGF-I, ALS and IGFBP-3 in a group of acromegalic patients. With the aim of simplifying the follow-up protocol in these patients we also tested if one single sample taken after glucose load could replace the nadir value. DESIGN AND MEASUREMENTS GH secretion was evaluated by oral glucose tolerance test (OGTT), and by studying spontaneous secretion (GH day curve) with sampling at hourly intervals from 08.00 to 18.00 h; from the day curve, mean (MGHDC) and minimum (TRGH) values were considered. IGF-I, ALS, and IGFBP-3 were measured in the basal state at the first testing. PATIENTS Fifty acromegalic patients (26-83 years, 31 females, 19 males) in various phases of disease activity. Forty-two patients had previously undergone pituitary surgery (10 also radiotherapy), 23 were treated with SMS analogues and three with dopamine agonist drugs. RESULTS The nadir GH value after glucose load correlated most significantly with the 120th-minute sample (R = 0.95). Comparison of the postglucose 120th minute at the two cut-off values with IGF-I, IGFBP-3 and ALS showed higher concordance of postglucose level at 0.3 with IGF-I, while concordance was similar for the two cut-off values with ALS and IGFBP-3. When the 120th minute postglucose GH value is lower than 1 mug/l and IGF-I is within 2SD for age nearly all other parameters are normal. IGF-I correlated more with ALS (R = 0.78) than with IGFBP-3 (R = 0.50) and the latter was less concordant with GH secretion parameters than the previous two. CONCLUSIONS A sample taken at the 120th minute after glucose load, together with IGF-I and/or ALS evaluation can give sufficient information for a routine assessment of disease activity, both in the diagnosis and in the follow-up to treatment. If GH is lower than 1 mug/l and IGF-I/ALS are normal, then the patient can be classified as 'nonactive' or 'controlled'; a pathological IGF-I and/or ALS value is a sign of disease activity irrespective of the GH values, while normal IGF-I/ALS with an elevated GH requires further assessment.