Endocrine Abstracts

Introduction: The insulin tolerance test (ITT) is the gold standard for hypothalamic–pituitary adrenal axis assessment. There are different protocols depending on the number and timing of serum samples. Our study aimed to investigate the kinetics of serum glucose and cortisol levels during ITT and to determine the most appropriate times for blood samples.

Methods: Our study was cross-sectional and descriptive. One hundred patients with suspected adrenal insufficiency (AI) were evaluated. The patients had 12 h fasting prior to the ITT. An intravenous rapid insulin bolus of 0.1 to 0.2 units/kg was administrated. Eight serum samples for glucose and cortisol measurements were taken: before the insulin injection (T0), at the time of hypoglycemia (Thypo) and samples every 10 min for 60 min after hypoglycemia (T10, T20, T30, T40, T50 and T60). We considered an adequate response a serum cortisol level above or equal to 18 μg/dl after a serum glucose level below 40 mg/dl.

Results: The mean age was 41.4±15.2 years and the sex ratio (F/H) was 0.2. The mean serum glucose lower cut point was 0.29±0.07 g/l and the mean time to achieve venous hypoglycemia (below 0.40 g/l) was 27.9±8.7 min. Forty-two patients (42%) had an adequate response and 58 patients (58%) had AI. Basal cortisol level was correlated with serum cortisol peak (r=0.56 P<0.001). A cutoff point of 9.75 μg/dl had a sensitivity of 59% and a specificity of 73% to predict an adequate response, it for. Twenty-six patients (62%) had an early response and 16 patients (38%) had a late response. A basal cortisol level ≤11.2 μg/dl had a sensitivity of 62% and a specificity of 82% to predict a late response. Finally, the most appropriate times for serum cortisol measurements were T30, T40 and T50 or T20, T30 and T50 with a sensitivity of 95%.

Conclusions: It is necessary to multiply the number of cortisol level samples after hypoglycemia, especially beyond 30 min, in order to increase the sensitivity of ITT and avoid misdiagnosis.

Key words: cortisol, insulin, hypoglycemia, adrenal insufficiency, diagnosis