ASSESSMENT OF GH STATUS IN ACROMEGALY USING SERUM GROWTH-HORMONE, SERUM INSULIN-LIKE GROWTH-FACTOR-I AND URINARY GROWTH-HORMONE EXCRETION

OBJECTIVE It is still not clear what is the most suitable method for m onitoring progress of acromegaly. The aim of this study was to assess the relative merits of serum GH, serum IGF-I and urinary GH (UGH) excr etion in the follow-up of acromegalic subjects. SUBJECTS AND METHODS T hirty-six acromegalic patients each had a GH day series performed cons isting of five serum GH measurements, together with an estimate of ser um IGF-I and UGH. The first sample taken for serum GH was fasting (bas al) whilst the third (1430 h) was arbitrarily chosen as a random value . UGH was measured from two overnight collections and the mean value u sed for subsequent data analysis. MEASUREMENTS Serum GH and IGF-I were measured by radioimmunoassay whilst UGH was estimated by an immunorad iometric assay using commercially available reagents. RESULTS There is a highly significant linear correlation between serum GH and IGF-I fo llowing log transformation of these two variables (r=0.85; P<0.0001). Analysis of the raw data shows that the relation is in fact curvilinea r rendering IGF-I less useful as a surrogate for integrated GH secreti on at high levels of serum GH. There is a strong linear correlation be tween both a singleton basal serum GH and uGH (r=0.78; P<0.001) and th e mean of five measurements (day series) and UGH (r=0.81; P<0.0001). B oth uGH and IGF-I are excellent predictors of those patients with pers istent elevation of serum GH, identifying 95 and 96% respectively with serum GH>5 mU/l, We have identified a number of patients, however, wi th persistent elevation of IGF-I in the presence of serum GH<5 mU/l an d normal uGH. Until the significance of these findings with respect to long-term outcome is known, serum GH should continue to be used in th e follow-up of these patients. An alternative, which reflects integrat ed overnight GH secretion, is UGH which is convenient and easy to coll ect as an outpatient and correlates strongly with serum GH. CONCLUSION Acromegalic patients can be conveniently followed on an outpatient ba sis using a combination of UGH and serum IGF-I. Measurements of serum GH can be reserved for those with discrepant results.