Endocrine Abstracts (2004) 7 P87

Association between serum insulin-like growth factor-1 and serum growth hormone levels across an oral glucose tolerance test in assessing disease activity in acromegaly

J Ayuk, SE Stewart, MC Sheppard & PM Stewart

Division of Medical Sciences, University of Birmingham, Queen Elizabeth Hospital, Birmingham, UK.

Debate surrounds the optimal biochemical assessment in the follow-up of patients with

acromegaly, particularly with the introduction of GH receptor antagonists to the treatment algorithm. Consensus statements suggest target values for GH of < 1microgram per litre with normal age and sex matched IGF-1 values. A number of groups have reported on the correlation between IGF-1 and GH levels in small cohorts of acromegalic patients. We retrospectively

analysed IGF-1 and GH data from 349 OGTTs performed on 108 patients (63 females) diagnosed with acromegaly between 1966 and 2001 and with varying degrees of disease activity. Mean age at diagnosis was 45 years (range 16-69). 70 patients had macroadenomas. 24 were treated with primary medical therapy while 84 had been treated with surgery and/or radiotherapy. The

association between simultaneous serum IGF-1 and mean, fasting, nadir and peak GH levels was explored using Spearman correlation analysis. Overall there was a strongly positive correlation between IGF-1 and mean (r=0.66, p<0.0001), fasting (r=0.62, p<0.0001) and nadir (r=0.70, p<0.0001) GH levels. This correlation remained when the confounding effect of repeated measurements on the same patient was eliminated by restricting analysis to the first assessment performed on each patient (mean r=0.67*, fasting r=0.61*, nadir r=0.70*; *p<0.0001). However, only 58% of patients with normal age-matched IGF-1 levels had a nadir GH < 2mU/L, while 87% with elevated IGF-1 levels had a nadir GH > 2mU/L. The correlation

between IGF-1 levels and mean GH levels varied according to treatment modality, ranging from r=0.61 (p<0.0001) with primary medical therapy to r=0.72 (p<0.0001) with surgery. The correlation was stronger in males (r=0.77, p<0.0001) than in females (r=0.58, p<0.0001). We conclude that IGF-1 levels correlate most strongly with nadir GH during an OGTT in patients with acromegaly, but normal IGF-1 levels do not always predict a nadir GH less than 2mU/L.

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