Endocrine Abstracts

Introduction

The insulin tolerance test (ITT) is the gold standard for the assessment of the integrity of the hyopothalamo-pituitray adrenal axis. it’s major drawbacks are the mandatory presence of an experienced physician and continuous supervision to detect any complication. Our study aims to evaluate the indications and the outcomes of the ITT performed in our department.

Patients and methods

We conducted a retrospective study of 38 patients with suspected adrenal insufficiency (AI) who underwent the ITT over two years (2018–2019) in our endocrinology department. The patients had 12 hours fasting prior to the test. Intravenous insulin ( actrapid ) was administrated. The insulin dose was determined from body weight and adjusted based on insulin resistance: 0.2 IU/Kg if the patient was considered to be insulin resistant and 0.1 IU/Kg in other cases. Four blood samples for glucose and cortisol measurements were taken: before the insulin injection (T0), at blood glucose < 50 mg/dl (T1), at 15 min (T2) and at 30min (T3) after achieved hypoglycemia. A meal was given at the moment of hypoglycemia after T1 measurements.

Results

The ITT was performed in 38 patients (10 male, 28 female). The mean age was 40.6 ± 16.4 years (range 10–72 years). Fourteen patients underwent the test for underlying pituitary adenoma, 14 patients for clinical symptoms (7 patients) or biological assessments (7 patients) (hypoglycemia, low cortisol levels.) suggesting an AI, 2 patients for a traumatic brain injury, 2 for pituitary surgery, 2 for bilateral adrenalectomy and 2 for associated autoimmune disease. Adequate hypoglycemia (venous plasma glucose < 50 mg/dl was achieved in 36 patients (94, 7%), of that 8, 7% had no symptoms, while only 2 patients had neuroglucopaenic symptoms. There were no significant adverse events recorded. Eight patients showed an adequate cortisol response (> 18 µg/dl ) with a mean serum cortisol 12.5 ± 3.8 µg/dl (T0), 15.9 ± 3.5 µg/dl (T1), 19.11 ± 2.8 µg/dl (T2) and 20.6 ± 1.9 µg/dl (T3). Twenty-eight patients showed an inadequate cortisol response, their levels of serum cortisol were: 8.3 ± 2.9 µg/dl (T0), 7.9 ± 2.7 µg/dl (T1), 10.9 ± 2.8 µg/dl (T2) and 12.4 ± 3.9 µg/dl (T3).

Conclusion

The ITT is a safe test when conducted in optimal settings. The insulin dose should be well determined to obtain appropriate hypoglycemia. Additional time and number of sampling are required to avoid misclassification and to increase the specificity of the test.