Measurement of cortisol in serum and saliva
- Lynnette K Nieman, MD
Lynnette K Nieman, MD
- Section Editor — Adrenal Disease
- Senior Investigator
- Bethesda, MD
Measurements of cortisol in serum (or occasionally plasma) are extremely useful in the diagnosis of hypercortisolism and adrenal insufficiency. It is important to appreciate the many factors that can affect the serum cortisol concentration and in particular the episodic secretion of cortisol and the resulting diurnal variation in serum cortisol, which makes the interpretation of a single value hazardous. Measurements of the salivary cortisol may offer some advantages over measurements of serum cortisol. Methods of interpretation of cortisol assays will be reviewed here. Their use in the diagnosis of adrenal disorders is reviewed separately. (See "Establishing the diagnosis of Cushing's syndrome" and "Diagnosis of adrenal insufficiency in adults".)
MEASUREMENT OF SERUM CORTISOL
Cortisol has been measured in serum by several methods. Although many of them are no longer in routine use, the important assays are mentioned to permit one to interpret the older literature.
Methods of measurement
Porter-Silber chromogens — Serum cortisol was first measured by assay of Porter-Silber chromogens (17,21-dihydroxy-20-ketosteroids, referred to as 17-hydroxycorticosteroids, or 17-OHCS) . This method is no longer used.
Competitive protein-binding assay — This assay uses competition for binding sites on cortisol-binding globulin (CBG, or transcortin) to quantify cortisol [2,3]. Its advantage is lack of drug interference; its disadvantage is that prednisolone and several endogenous steroids, some of which may be increased in pregnancy, adrenal carcinoma, congenital adrenal hyperplasia, and after administration of adrenal enzyme inhibitors, bind to CBG and falsely elevate serum cortisol values. Interfering steroids can be removed before assay by solvent partition or thin layer chromatography (TLC).
Fluorometric assay — This assay exploits the fluorescence of 4-11-beta, 21-dihydroxy-3,20-ketosteroids (11-hydroxycorticosteroids, or 11-OHCS) in sulfuric acid and alcohol . Cortisol and corticosterone are detected by this assay; potent synthetic glucocorticoids are not. Its advantages are simplicity and relative specificity; its disadvantage is that spironolactone, quinine, quinidine, niacin, and benzoyl alcohol also fluoresce in those solvents and therefore falsely elevate cortisol values.
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- MEASUREMENT OF SERUM CORTISOL
- Methods of measurement
- - Porter-Silber chromogens
- - Competitive protein-binding assay
- - Fluorometric assay
- - Radioreceptor assay
- - Radioimmunoassay
- - Other immunoassays
- - Structurally-based assays
- Normal values
- Important caveats
- - CBG
- - Hepatic and renal dysfunction
- - Thyroid hormone
- - Body weight
- - Age
- - Depression
- - Synthetic glucocorticoids
- - Non-glucocorticoid drugs
- - Alcohol abuse
- - Sepsis
- SERUM FREE CORTISOL
- CORTISOL PRECURSORS
- Normal values
- MEASUREMENT OF SALIVARY CORTISOL CONCENTRATION
- Normal values