Cortisol Serum (Evening Sample)

The Cortisol Serum (Evening Sample) is a blood test that measures the level of cortisol, a steroid hormone produced by the adrenal gland. It is done in the evening because cortisol levels fluctuate throughout the day, typically peaking in the morning and dropping in the evening. This test helps diagnose conditions associated with adrenal gland functioning, such as Cushing’s syndrome or Addison’s disease.

Cortisol is a vital hormone produced by the adrenal glands, two small glands that are located above the kidneys. A gland in your brain, called the pituitary gland, makes a hormone that tells your adrenal glands how much cortisol to make.  

Cortisol affects almost every organ and tissue in your body. Its physiological functions include regulating carbohydrate metabolism and the distribution of electrolytes and water. Cortisol also has immunosuppressive and antiinflammatory activity hence it helps your body respond to stress (cortisol is sometimes called the "stress hormone"), reduce inflammation, regulate blood sugar and metabolism (how your body uses food for energy) and control blood pressure. If your cortisol levels are too high or too low, it may mean you have a disorder of your adrenal glands, a problem with your pituitary gland, or a tumor that makes cortisol.

Increased levels of cortisol are associated with Cushing syndrome, Adrenal and Pituitary adenoma/carcinoma, ectopic Adrenocorticotropic Hormone (ACTH) production, glucocorticoid therapy, stress, depression, hypoglycemia and hyperthyroidism. Decreased levels are seen in Addison's disease, generalized adrenal hypofunction or a defect in the metabolic pathway for cortisol biosynthesis.The Cortisol Serum (Evening Sample) test can help diagnose diseases such as Cushing syndrome and Addison’s disease which can lead to either too much or too little production of cortisol. This test also helps evaluate how well the pituitary and adrenal glands are working.

Cortisol levels in the body are controlled by ACTH, a hormone made by the pituitary gland. ACTH is released in response to another hormone called corticotropin-releasing hormone (CRH), which is produced by the hypothalamus. This process creates a daily cycle, with cortisol levels peaking in the early morning (6.am-8a.m) and dropping to their lowest point(nadirs) around 11 p.m.

The Cortisol Serum (Evening Sample) test is conducted in the evening to capture the natural decline in cortisol levels that typically occurs as part of the body’s circadian rhythm. Measuring cortisol levels later in the day can also help differentiate between normal cortisol levels and conditions like Cushing’s Syndrome, as cortisol levels naturally decrease towards evening. It is noteworthy that cortisol levels can be influenced by systemic diseases and stress. 

Discuss with your doctor regarding the exact time for sample collection, typically in the early evening, to ensure consistency with natural cortisol fluctuations. You may be asked not to do any vigorous exercise the day before the test.

Lab test results may vary across laboratories. Abnormal test results require an expert interpretation, therefore, never try to self-medicate at home based solely on these results, and always consult a doctor for proper understanding of the test results.