GROWTH HORMONE TESTING

Growth hormone stimulation tests in 25 children were reviewed to determine concordance among 3 tests, oral L-dopa, arginine infusion and insulin induced hypoglycemia. The validity of test results was examined using current growth velocity and response to hGH therapy. Patients were classified as to their ability to attain an hGH level of ≥ 6ng/ml on any of the 3 tests and then similarly on the basis of only 2 tests, L-dopa and arginine. Data from 25 patients with short stature who received all provocative tests were analysed. Eighteen of the 25 received DES prior to the tests. After an overnight fast, the 3 tests were done sequentially. Using all 3 tests for classification as to ability to produce an hGH level of ≥ 6ng/ml, 11 of 25 were classified nonresponders. Using only L-dopa and arginine results, 12 were nonresponders; 1 child had an hGH level ≥ 6ng/ml only in response to insulin. Eliminating insulin from our testing would have led to misclassifying 1 normal responder as abnormal, an error rate of 4%. Of the 11 classified as nonresponders, 3 had normal growth velocity. The 3 tests together yield an incidence of false abnormal results of 12%. Eliminating the insulin test raises the number of false abnormal tests to 16%. Using growth velocity to assess the validity of these tests, the 3 tests together were 88% accurate, and L-dopa and arginine only were 84% accurate. Insulin induced hypoglycemia added little information in the population reviewed. We propose it be eliminated from routine testing in favor of sequential oral L-dopa and arginine infusion tests with prior DES preparation.