A short acute octreotide test for response prediction of long-term treatment with somatostatin analogues in acromegalic patients

The usefulness of the acute octreotide test in the selection of acromegalic patients for chronic somatostatin depot analogues treatment is controversial. The aim of the present study was to determine its accuracy for chronic response prediction, and the reliability of a short version of the classic 6-hour test. The data from 26 acromegalics (19 women, 7 men, mean age 52.6 +/- 13.1 years) studied with an acute octreotide test (6 hours sampling for GH measurement after octreotide 100 mu g s.c.) were retrospectively analyzed. Eighteen of them followed chronic somatostatin depot analogues treatment for 12 months. GH nadir was always detected at 2 hours (mean decrease 75.9 +/- 24%). GH levels at 2 hours positively correlated with the other time-points (r(s), 0.97, 0.98, 0.97, 0.96 at 3,4,5 and 6h, respectively; p < 0.0001). During chronic treatment with maximal effective dose for 12 months, 61% of the patients achieved IGF1 < 3 SD and 22% reached lGF1 < 2 SD. GH nadir correlated with lGF1 decrease at 12 months (r(s), 0.76, p < 0001). GH nadir of 9.2 ng/ml predicts IGF1 < 3 SD with 82% sensitivity and 58% specificity (75% PPV, 67 % NPV); for IGF1 < 2 SD, 75 % sensitivity and 58 % specificity are obtained for GH nadir 3.6 ng/ ml, with 33 % PPV and 89 % NPV. Acute octreotide test reliably predicts response to long-term treatment; the short, 2-hour version is fully informative for therapeutic decisions in acromegalic patients.