Objective: It is still not clear what is the most suitable method for monitoring progress of acromegaly. The aim of this study was to assess the relative merits of serum GH, serum IGF-I and urinary GH (uGH) excretion in the follow-up of acromegalic subjects.
Subjects and methods: Thirty-six acromegalic patients each had a GH day series performed consisting of five serum GH measurements, together with an estimate of serum IGF-I and uGH. The first sample taken for serum GH was fasting (basal) whilst the third (1430h) was arbitrarily chosen as a random value. uGH was measured from two overnight collections and the mean value used for subsequent data analysis.
Measurements: Serum GH and IGF-I were measured by radioimmunoassay whilst uGH was estimated by an immunoradiometric assay using commercially available reagents.
Results: There is a highly significant linear correlation between serum GH and IGF-I following log transformation of these two variables (r = 0.85; P < 0.0001). Analysis of the raw data shows that the relation is in fact curvilinear rendering IGF-I less useful as a surrogate for integrated GH secretion at high levels of serum GH. There is a strong linear correlation between both a singleton basal serum GH and uGH (r = 0.78; P < 0.001) and the mean of five measurements (day series) and uGH (r = 0.81; P < 0.0001). Both uGH and IGF-I are excellent predictors of those patients with persistent elevation of serum GH, identifying 95 and 96% respectively with serum GH > 5mU/l. We have identified a number of patients, however, with persistent elevation of IGF-I in the presence of serum GH < 5mU/l and normal uGH. Until the significance of these findings with respect to long-term outcome is known, serum GH should continue to be used in the follow-up of these patients. An alternative, which reflects integrated overnight GH secretion, is uGH which is convenient and easy to collect as an outpatient and correlates strongly with serum GH.
Conclusion: Acromegalic patients can be conveniently followed on an outpatient basis using a combination of uGH and serum IGF-I. Measurements of serum GH can be reserved for those with discrepant results.