Background
Cortisol, also known as hydrocortisone, is the primary coricosteroid secreted by the adrenal cortex.  Cortisol is synthesized from cholesterol and may be found in the blood as free cortisol or bound to corticosteriod-binding globulin.  The release of cortisol is controlled by Adrenocorticotropic hormone (ACTH) which is produced in the anterior pituitary.  Plasma cortisol levels are highest in the morning and decrease throughout the day.  Cortisol concentration in plasma also elevates in response to stress.  Cortisol has an anti-inflammatory effect and aids in carbohydrate metabolism, renal function and the promotion of glucogenesis.

Measurement of plasma cortisol levels is useful in diagnosing conditions related to functions of the adrenal cortex, including Cushing’s syndrome (hypercortisolism), Addison’s disease (hypocortisolism) and adrenal tumors.  Abnormal cortisol levels may also possibly be linked to prostate cancer, depression and schizophrenia.

Assay Principle
This is an ELISA for the quantitative analysis of Cortisol levels in biological fluid.  This test kit operates on the basis of competition between the hormone conjugate and the Cortisol in the sample for a limited number of binding sites on the antibody coated plate.

The sample or standard solution is first added to the microplate.  Next, the diluted hormone conjugate is added and the mixture is shaken and incubated at room temperature for one hour.  During the incubation, competition for binding sites is taking place.  The plate is then washed removing all the unbound material.  The bound hormone conjugate is detected by the addition of substrate which generates an optimal color after 30 minutes. Quantitative test results may be obtained by measuring and comparing the absorbance reading of the wells of the samples against the standards with a microplate reader at 450nm or 650nm.  The extent of color development is inversely proportional to the amount of Cortisol in the sample or standard.  For example, the absence of Cortisol in the sample will result in a bright blue color, whereas the presence of Cortisol will result in decreased or no color development.

If using urine as a sample it is recommended to run our Creatinine Assay kit (CR01) in conjunction with your samples since urinary creatinine levels may be used to normalize the rate of excretion of other analytes.