Endocrine Abstracts

Introduction: Growth hormone stimulation test (GST) is pivotal in diagnosing Growth Hormone Deficiency (GHD). Two abnormal GSTs are usually required to diagnose GHD (NICE and BSPED guidelines). Our centre moved from Insulin Tolerance Test (ITT) as a first-line GST to Arginine stimulation test (AGT) considering the significant risks associated with ITT and the need for close medical supervision for a longer period.

Aim: To assess the specificity of AGT compared to ITT as a first-line GST in diagnosing GHD.

Methodology: Retrospective case notes review of 118 children who underwent AGT or ITT as the first GST (2019-2022) in diagnosing GHD. End of growth GST and patients with other pituitary hormone deficiencies or structural pituitary abnormalities and brain tumours were excluded. Peak GH level > 6.7 µg/l was considered normal response.

Results: 88 children (males-63, females-25) with a mean age of 9.26 years (range 2.94-16.71) and a mean baseline height SDS of -2.7 (-4.7-+0.6) had AGT as the first GST. 22 received sex steroid priming. 24 patients had a peak GH level <6.7μg/l. 16 had a second test (ITT or glucagon) to confirm GHD of which five were non-GH deficient (false positive 5.6%). Patients with false positives had a mean peak GH of 3.74μg/l (range 2.1-6.2) and all had normal IGF-1. 30 children with a mean age of 11.04 years (range 6.4-16.4) and a mean baseline height SD of -2.5 (-4.1-1) had ITT as the first GST. 14 were GH deficient on ITT of which 9 were confirmed as non-GH deficient with AGT (false positive 30%). The mean peak GH on false positives were 4.39μg/l (range 0.9-6) and 89%(n = 8) had normal IGF-1. In this cohort, the specificity of AGT is 92.75% (84.13%- 96.87%) with a positive predictive value (PPV) of 79.17% (95% CI- 59.53-90.76%) in contrast to specificity of 64% (95% CI 44.52-79.75) and PPV of 35.71% (95% CI 16.34-61.24) in ITT. AGT has a superior specificity in diagnosing GST in children compared to ITT(P = 0.0138)

Conclusion: We suggest AGT is a more specific test to diagnose GHD compared to ITT and is also less expensive in terms of resources.