Somatomedin C in treated acromegaly: poor correlation with growth hormone and clinical response

To determine the usefulness of commercially available somatomedin C levels in the evaluation of the treatment of acromegaly, 15 patients were tested at 0.25-15.4 yr after onset of therapy. Clinical response, as determined by a numerical scoring system, was compared with RIA of GH and somatomedin C. Symptomatic response was poorly correlated with somatomedin C (r = 0.033) as well as with GH (r = 0.24). The correlation of GH and somatomedin C was also poor (r = 0.46, P greater than 0.05). Eighty-three percent of patients with clinical improvement had GH less than or equal to 10 ng/ml, 50% had GH less than or equal to 5 ng/ml, while 42% had somatomedin C less than or equal to 3.0 U/ml. All patients who were evaluated at 1 yr or less after therapy had elevated somatomedin C levels with normal or near normal GH values. In contrast only 2 of 11 patients evaluated at more than 1 yr after therapy had a mild persistence of somatomedin C elevation with normal GH levels. Determination of somatomedin c costs more than GH determinations and appears to offer no apparent advantage over GH in following patients treated for acromegaly.