Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (848 page)

CORTISOL, SERUM

   Definition

   Cortisol (hydrocortisone) is the major glucocorticoid produced and secreted by the adrenal cortex. It affects the metabolism of protein, fat, and carbohydrates; maintenance of muscle and myocardial integrity; and the suppression of inflammatory and allergic activities.

   
Normal range:

   
AM
cortisol: 8.7–22.4 μg/dL

   
PM
cortisol: <10 μg/dL

   Use

   Discrimination between primary and secondary adrenal insufficiency

   Differential diagnosis of Cushing syndrome

   Interpretation

   The most common cause of increased plasma cortisol levels in women is a high circulating concentration of estrogen (e.g., estrogen therapy, pregnancy), resulting in increased concentration of cortisol-binding globulin.

   Patients with severe illness and sepsis have reduced cortisol-binding globulin and albumin levels, resulting in lowered cortisol levels.

   Limitations

   Bound cortisol circulates in an available but temporarily inactive state. The physiologic activity of cortisol depends on levels of the small fraction of circulating unbound cortisol.