Diurnal cortisol levels, dehydroepiandrosterone (DHEA), and secretory immunoglobulin A (sIgA) are used to evaluate adrenal function.

That is because they reflect the activity of the hypothalamic-pituitary-adrenal (HPA) axis and the immune system, which are closely related.

1. Diurnal cortisol levels: Cortisol is a hormone produced by the adrenal glands and is regulated by the HPA axis. Cortisol levels naturally fluctuate throughout the day, with peak levels in the morning and low levels at night. Abnormal cortisol patterns, such as high levels in the evening or nighttime, can indicate adrenal dysfunction.
2. DHEA: DHEA is a hormone produced by the adrenal glands and plays a role in regulating the immune system and metabolism. Low levels of DHEA can indicate adrenal insufficiency.
3. sIgA: sIgA is a protein produced by the immune system and plays a role in protecting against infection. Low levels of sIgA can indicate adrenal dysfunction, as cortisol is also involved in regulating the immune system.

Together, these measurements can provide a comprehensive evaluation of adrenal function and help to identify any underlying HPA axis or immune system dysregulation. However, it is important to note that these tests should be interpreted in the context of a patient’s overall clinical presentation and should be used in conjunction with other tests and assessments.