EVALUATION OF ACROMEGALY BY RADIOIMMUNOASSAY OF SOMATOMEDIN-C

We measured serum concentrations of somatomedin-C by radioimmunoassay in 57 acromegalic patients and compared them with various indicators of disease activity. The mean fasting somatomedin-C concentration was 6.8 U per milliliter (range, 2.6 to 21.7) for the acromegalics and 0.67 U per milliliter (range, 0.31 to 1.4) for 48 normal, fasting adults. The somatomedin-C concentration correlated significantly with: heel-pad thickness (r = 0.73), fasting glucose (r = 0.74), and one-hour postprandial glucose (r = 0.77). In contrast, “glucose-suppressed” growth hormone correlated weakly (r = 0.34, 0.36, 0.34) with these clinical indexes of severity. Fasting growth hormone levels showed no correlation (r = 0.14). Five active acromegalics had “normal” growth hormone levels after glucose suppression, but they had elevated somatomedin-C. In 15 patients studied one year after treatment, changes in somatomedin-C concentrations paralleled the degree of clinical improvement. Measurement of somatomedin-C appears to provide a reliable means for confirming the diagnosis of acromegaly and of clinical disease activity than measurement of growth hormone concentrations. (N Engl J Med 301:1138–1142, 1979) THE diagnosis of acromegaly is confirmed by measuring serum growth hormone concentrations under basal conditions and after a glucose-suppression test. Clinical evaluation is sometimes unreliable since the signs and symptoms of acromegaly vary in severity and may fail to regress with reduced secretion of growth hormone.1 Although the concentration of serum growth hormone usually confirms the diagnosis, it may not correlate with the 24-hour growth hormone-secretory rate2 or the severity of the illness.3 4 5 This lack of correlation has been attributed to wide fluctuations of basal levels, paradoxical responses to glucose administration, or the variable sensitivity of a given patient to. © 1979, Massachusetts Medical Society. All rights reserved.