Endocrine Abstracts

In many centres a test dose (TD) of octreotide is administered prior to commencing LAR. The value of the TD as a predictor of subsequent response to therapy remains uncertain. We have studied the relationship of the GH response to a TD to the subsequent response to LAR in 26 patients (median age 59 years, range 20- 84). After baseline GH sampling, 50mcg subcutaneous octreotide was administered and sampling continued for six hours. Results of the TD were compared to the lowest mean GH achieved on LAR (77% achieved target GH of <5mU/l).

Median baseline GH was 17.7mU/l (range 2.2 to 180) and during the TD fell by a median of 76.7% (43.1 to 97.1) to a median of GH 3.4mU/l (1.0 to 26.6), with a positive correlation between baseline GH and nadir GH (r=0.733, p<0.001). Furthermore, a correlation was found between the nadir GH during the TD and the subsequent GH response to LAR (r=0.52, p=0.003), no such relationship existed for % fall in GH during the TD. Optimal predictive value of the TD was achieved with a TD GH nadir of <5mU/l. At this level the positive predictive value of the TD for a subsequent mean GH on LAR of <5mU/l was 87%, and 85% for >50% fall, but the former had a better negative predictive value of 50% compared to 0% for % fall.

Dividing patients by baseline GH <25, 25-50 and >50 mU/l reveals 87%, 33% and 0% respectively achieve a nadir GH <5mU/l during the TD, and during LAR 87%, 67% and 50% respectively achieve GH <5mU/l.

A relatively low baseline GH and a nadir during the TD of <5mU/l are both predictive of a good response to LAR therapy but a poor response during a TD does not exclude a good response to LAR therapy.