Introduction: The presence of glucose metabolism disorders and their possible correlation with degree of cortisol secretion were evaluated in patients with non-functioning adrenal incidentalomas (NFAIs).

Material and methods: The study group consisted of 131 patients with hormonally inactive adrenal incidentalomas. In each patient, besides hormonal and radiological evaluation, was assessed for fasting glucose and insulin concentrations, and the oral glucose tolerance test (OGTT) was performed in all participants without previous history of glucose disturbances. The HOMA-IR, QUICKI, and TyG indices were calculated.

Results: Diabetes was diagnosed in 30.5% of the studied group. Among glucose tolerance abnormalities, impaired fasting glucose (IFG) was found in 23.7%, impaired glucose tolerance (IGT) in 4.6%, and combined IFG and IGT in 11.5%. Normoglycaemia was recognised in 29.8% of NFAIs patients. The occurrence rate of glucose aberrations increased with age. There was a significant difference in all insulin resistance indices shown between normoglycaemic patients and those with impairments in glucose tolerance. There was no significant correlation between fasting glucose, insulin resistance indices, and adrenal tumour size or degree of cortisol secretion.

Conclusions: The prevalence of diabetes and impaired fasting glucose among NFAIs patients is much higher than in the general population. Therefore, patients with incidentally discovered adrenal tumours should be tested for glucose tolerance.