Endocrine Abstracts

Background: The ITT has been said to be the gold standard for diagnosing GH deficiency (GHD) for 50 years. The original 0, 20, 30, 60, 90 and 120 min time points are still used in many but a survey of current UK paediatric ITT protocols identified several variations.

Objective and hypotheses: To identify optimal GH sampling time points to avoid over diagnosis of GHD.

Methods: Results of 502 paediatric ITTs using two different sampling protocols (P1 n=459 with time points: −30, 0, 30, 60, 90, 120 min and P2 n=43 with time points −30, 0, 20, 30, 45, 60, 75, 90 min). GH deficiency (GHD) was defined by peak GH <7 μg/l for paediatric or <5 μg/l in transition age-ranges.

Results: Hypoglycaemia was achieved in 97% of tests. With P1, peak GH was measured (in decreasing order of frequency) at 60, 30, 0, −30, 90 and 120 min (46, 20, 15, 13, 4 and 1% respectively) while with P2 at 45 (25%), 60, −30, 0, 30 min (16% each).

GH concentrations above the age related cut-offs at −30 min were seen in 21 cases and represented the maximum level in 16 of them. This precluded GHD in 3% of cases (16/502). Using the same criteria, GH was precluded with the 45 min sample in 2/43 tests (5%) and with the 75 min in 1/43 tests (2%). The 90 and 120 min samples did not preclude GHD.

Conclusions: GH peaks that preclude GHD can be seen in samples even before the administration of insulin in 3% of children. 45 and 75 min samples precluded GHD deficiency in an additional 5–10% of children, avoiding potentially inappropriate and costly GH treatment or repeat tests. 120 min sampling did not contribute to GHD diagnosis.