Growth hormone (GH) provocation tests and the response to GH treatment in GH deficiency

OBJECTIVE: To identify factors, particularly the growth hormone (GH) provocation test result, affecting growth response to GH treatment in children with GH deficiency (GHD). SUBJECTS: A total of 337 prepubertal GHD patients aged <10 years from the UK Pharmacia KIGS database (GH response to provocation test <20 mU/l). OUTCOME MEASURE: Annual change in height standard deviation score (SDS) (revised UK reference) in the first and second years of treatment. RESULTS: Height increased by 0.74 SDS units (SD 0.39) in the first year of treatment and 0.37 units (SD 0.27) in the second. Adjusting for age, height, weight, midparent height, and injection frequency, the strongest predictor of first year growth response was the GH provocation test result; halving the result predicted an extra height increment of 0.09 units (p<0.0001). It predicted the second year response less well (p<0.0002) and after adjusting for the first year response was not predictive at all. CONCLUSIONS: Among patients referred for possible GHD, the GH provocation test, though not a gold standard for diagnosis, is a valuable predictor of growth response in the first year of treatment. A year's treatment is recommended for cases with a marginal provocation test result, with the option to continue treatment if the response is adequate. The value of unified protocols for single or repeated provocation tests needs to be assessed.