Endocrine Abstracts

Introduction: Insulin stress test (IST) has long been the gold standard for testing the hypothalamus-pituitary–adrenal (HPA) axis. There are concerns about the safety of IST as hypoglycaemia can give rise to various symptoms including seizure and coma although this is rarely seen in clinical practice. Hyperinsulinaemic hypoglycaemic clamp is a common research procedure used to induce hypoglycaemia in a step-wise fashion to study the effect of hypoglycaemia.

Method: We modified the clamp procedure, aiming to reach nadir glucose of just under 2.4 mmol/l using a set insulin infusion protocol and variable rate dextrose infusion. We recruited patient referred from endocrine clinic for HPA axis assessment. Participants underwent both IST and modified clamp study at least 2 weeks apart. The primary outcome is to compare the nadir glucose level between routine IST and modified clamp. We also compared the peak cortisol and growth hormone in both the procedures.

Results: Total of nine patients were recruited, with two patients having HPA axis failure. Data reported as mean±S.D. in IST and modified clamp respectively. In all participants, the nadir glucose was 1.6±0.4 vs 2.0±0.3 mmol/l (P=0.007). Peak cortisol was 539±312 vs 531±341 nmol/l (P=0.815) and peak growth hormone was 2.4±2.1 vs 4.1±3.2 μg/l (P=0.031). In participants with intact HPA axis, the nadir glucose was 1.5±0.4 vs 2±0.3 mmol/L (P=0.023), peak cortisol 663±222 vs 656±270 nmol/l (P=0.878), and peak growth hormone 2.9±2.1 vs 5.1±2.9 μg/l (P=0.028). In participants with HPA axis failure, the nadir glucose was 1.9±0.1 vs 2.2±0 mmol/l (P=0.09), peak cortisol 106±9 vs 94±30 nmol/l (P=0.570), and peak growth hormone 0.5±0.3 vs 0.5±0.1 μg/l (P=0.861).

Conclusion: Modified clamp might be a safer way to assess the HPA axis with a higher nadir glucose level compared to IST with similar peak cortisol and growth hormone response.