Overview
Cortisol is a vital glucocorticoid hormone released by the adrenal glands, which are situated above the kidneys. Its secretion is regulated by adrenocorticotropic hormone (ACTH) from the pituitary gland, forming an essential part of the hypothalamic–pituitary–adrenal (HPA) axis. Cortisol plays a crucial role in helping the body respond to stress and is therefore commonly referred to as the “stress hormone.”
Physiologically, cortisol influences metabolism, immune function, nervous system activity, blood pressure, and blood glucose regulation. It counterbalances the action of insulin by increasing blood glucose through the release of stored glucose, while insulin acts to lower blood sugar. Both elevated and reduced cortisol levels can adversely affect health.
Symptoms
Abnormal cortisol levels manifest in diverse clinical symptoms.
Low cortisol levels (hypocortisolism), as seen in Addison’s disease, may present with severe weakness, fatigue, dizziness, confusion, muscle and joint pain, abdominal pain, vomiting, diarrhea leading to dehydration, reduced consciousness or delirium, mood changes, skin darkening, and low blood pressure.
High cortisol levels (hypercortisolism), associated with Cushing’s syndrome, may also cause fatigue, mood changes, muscle weakness, metabolic disturbances, and immune suppression. Cortisol imbalance significantly impacts overall physical and mental well-being.
Causes
Cortisol imbalance can arise from disorders affecting different levels of the HPA axis.
- Primary adrenal insufficiency (Addison’s disease) results from direct damage to the adrenal glands, leading to low cortisol levels.
- Secondary adrenal insufficiency occurs due to inadequate ACTH secretion from the pituitary gland.
- Tertiary adrenal insufficiency is caused by impaired corticotropin-releasing hormone (CRH) production from the hypothalamus.
Excess cortisol production may occur in endogenous Cushing’s syndrome, which can be caused by ACTH-producing pituitary adenomas, ectopic ACTH-producing tumors, adrenal gland tumors, or adrenal disease. Genetic conditions such as Multiple Endocrine Neoplasia type 1 (MEN1) and Familial Isolated Pituitary Adenomas (FIPA) may also contribute to cortisol excess.
Risk Factors
Individuals at increased risk for cortisol abnormalities include patients with adrenal, pituitary, or hypothalamic disorders, those experiencing chronic or severe stress, and individuals with a genetic predisposition to endocrine tumors. Acutely ill patients may exhibit transiently elevated cortisol levels due to stress-induced ACTH secretion.
Patients presenting with unexplained fatigue, muscle weakness, blood pressure abnormalities, metabolic disturbances, or pigmentation changes should be evaluated for cortisol imbalance.
Prevention and Diagnostic Approach
Cortisol levels vary according to the time of day, necessitating proper timing of sample collection for accurate interpretation. Blood samples are collected twice daily:
- 8:00 AM, when cortisol levels are at their peak
- 4:00 PM, when cortisol levels are at their lowest
Additionally, 24-hour urine cortisol testing is used, with boric acid added as a preservative at the start of collection and proper patient instructions provided.
Normal serum cortisol ranges:
- 8:00 AM: 10–20 µg/dL
- 4:00 PM: 3–10 µg/dL
Cortisol measurement methods include immunoenzymatic assays, quantitative electrochemiluminescent immunoassays, and mass spectrometry.
The cortisol-to-creatinine ratio is also used in diagnostic evaluation, where values greater than 17.5 × 10⁶ may indicate the presence of Cushing’s syndrome.
Interpretation of cortisol results must be correlated with ACTH levels:
- High cortisol with low ACTH suggests an adrenal tumor
- High cortisol with high ACTH indicates a pituitary tumor
- Low cortisol with low ACTH points toward hypopituitary adrenal insufficiency
- Low cortisol with high ACTH suggests adrenal gland damage
Clinical Significance
Serum cortisol testing is central to the diagnosis and management of adrenal disorders such as Addison’s disease and Cushing’s syndrome. However, cortisol estimation alone cannot identify the underlying cause of abnormal levels. Further hormonal evaluation and diagnostic testing are required to determine the exact etiology and guide appropriate treatment.
