Cortisol (Serum)

Cortisol is the body's primary stress hormone, produced by the adrenal glands and regulated by the pituitary gland. It plays a central role in blood sugar control, blood pressure regulation, immune function, and the body's response to physical and emotional stress. A serum cortisol test measures the amount of cortisol circulating in the bloodstream at the time of collection, offering a direct snapshot of adrenal function.

This test is typically requested when a clinician suspects an adrenal disorder, such as Addison's disease (adrenal insufficiency), Cushing's syndrome (cortisol excess), or when investigating persistent fatigue, unexplained weight changes, low blood pressure, or symptoms of hormonal imbalance. It is also used to monitor patients already receiving steroid therapy or those with known pituitary or adrenal conditions.

Because cortisol levels fluctuate naturally throughout the day, the timing of the sample is important. Morning collections are most common, as cortisol typically peaks shortly after waking. Your clinician will advise on the most appropriate timing for your circumstances.

Biomarkers

Adrenal Hormones
- Serum cortisol

Why it matters
Cortisol affects nearly every organ system in the body. Abnormal levels can manifest as chronic fatigue, anxiety, weight gain or loss, high blood pressure, poor immune response, and disrupted sleep. Identifying whether cortisol is too high or too low is the first step towards targeted treatment, whether that involves medication, lifestyle adjustment, or specialist endocrine referral. A clear, accurate cortisol result gives you and your doctor the foundation for informed decisions about your hormonal health.