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Laboratory Medicine

Test Directory / Cortisol


Brown clotted serum, gel barrier

Common AbbreviationsCort, Cor
Tube typeBrown clotted serum, gel barrier
Clinical IndicationCirculating cortisol levels follow a diurnal pattern in healthy individuals. Levels are highest in the morning after waking and lowest in the evening. Disorders of the hypothalamic-pituitary adrenal axis override this diurnal pattern. Decreased cortisol levels are caused by either primary or secondary adrenal insufficiency. Addison’s disease is caused by primary adrenal insufficiency due to metabolic errors or destruction of the adrenal cortex. Secondary adrenal insufficiency is caused by pituitary destruction or failure, resulting in loss of ACTH stimulation of the adrenal gland. Cushing’s syndrome is caused by increased levels of cortisol due to either primary or secondary adrenal hyperfunction. Please note that a 24-hour urinary cortisol measurement is the method of choice in the initial screening for Cushing’s syndrome not serum cortisol. Increased cortisol levels are induced by pregnancy and by stress due to depression, trauma, surgery, hypoglycemia, alcoholism, uncontrolled diabetes, and starvation.
Specimen TypeBlood
Sample typeSerum
Minimum Volume0.5mL If requesting more than 10 tests please send an additional brown clotted serum sample.
Special PrecautionsNo special requirements
Stability24 hours at 20 - 25°C, 4 days at 2 - 8°C and 12 months at -20°C
Turnaround TimeInpatient: 24 hours Outpatient/ GP: 24 hours
LaboratoryYork and Scarborough
Reference IntervalSamples collected between 6 - 10am: 133 - 537 nmol/L (Quoted by manufacturer)
LimitationsAnalysis should not be performed on grossly haemolysed, icteric or lipaemic samples. The assay is unaffected by biotin < 287 nmol/L or < 70 ng/mL. No interference was observed from rheumatoid factors up to a concentration of 600 IU/mL. No interference was observed from IgG < 5.0 g/dL; IgA < 1.0 g/dL; IgM < 1.0 g/dL Samples should not be taken from patients receiving therapy with high biotin doses (i.e. > 5 mg/day) until at least 8 hours following the last biotin administration. In vitro tests were performed on 16 commonly used pharmaceuticals. No interference with the assay was found. In rare cases, interference due to extremely high titres of antibodies to analyte specific antibodies, streptavidin or ruthenium can occur. In samples from patients who have been treated with prednisolone, 6Methylprednisolone or prednisone, falsely elevated concentrations of cortisol may be determined. During metyrapon tests, 11deoxycortisol levels are elevated. Falsely elevated cortisol values may be determined due to cross reactions. . Patients suffering from 21hydroxylase deficiency exhibit elevated 21deoxycortisol levels and this can also give rise to falsely elevated cortisol results.
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