GH Stimulation testing is unnecessary in patients with hypothalamic–pituitary disease, preserved pituitary function, and IGF-I SDS ≥ 0

PURPOSE: In adults with hypothalamic-pituitary disease, the presence of at least three additional pituitary hormone deficiencies, with or without markedly reduced IGF-I levels, is considered diagnostic of growth hormone deficiency (GHD) without the need for stimulation testing. In all other cases, dynamic testing is required despite its well-recognized limitations. To date, no formal strategy has been proposed to exclude GHD without performing stimulation tests. This study aims to develop a probabilistic model to estimate the likelihood of GHD in adults with hypothalamic-pituitary disease but no additional pituitary hormone deficiencies, based on IGF-I standard deviation scores (SDS). METHODS: We combined literature-derived data on: (1) the probability of an impaired GH response to stimulation tests in patients with hypothalamic-pituitary disease and preserved anterior pituitary function; and (2) the probability that adults with isolated GHD present IGF-I SDS values ≥ 0, ≥ 0.5, or ≥ 1. A Bayesian approach was applied to estimate the post-test probability of GHD in patients meeting these criteria. RESULT: Across all models, the estimated probability of adult-onset GHD ranged from 6.5% to 19.8%, while the probability of childhood-onset GHD ranged from 2.9% to 9.1%, consistently remaining below 20%, regardless of the IGF-I SDS cut-off applied. CONCLUSION: In adults with hypothalamic-pituitary disease but no additional hormonal deficiencies, IGF-I SDS values ≥ 0 identify a subgroup with a low, clinically acceptable probability of GHD, in whom stimulation testing may reasonably be avoided. This proof-of-concept model supports a simplified, probability-based diagnostic approach.