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PTD - 212

Test Directory -  Cortisol


Compound F

Clinical Indications

For the investigation of possible Addison's disease (primary adrenocortical insufficiency) or Cushing's disease. Monitoring steroid replacement.

Request Form

Combined Pathology Blood form (Yellow/Black)


On request. 

Specific Criteria

Same day

Patient Preparation

Cortisol shows considerable diurnal variation and samples must be collected between 8.00am and 9.00am for meaningful results to be obtained.

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


If an ACTH is also requested the samples must be collected at Basildon Hospital and brought to the laboratory immediately.

Turnaround Time

Same day




2 ml


Yellow top (SST) tube or

Paediatric orange top (lithium-heparin)

Causes for Rejection

Unlabelled sample.

Reference Range

Early morning sample: 171 - 536 nmol/L

Random sample: 65 - 536 nmol/L

Reference: Roche method insert


Critical Difference 58 nmol/L

Investigation of Addison's. Normal results do not exclude Addison's and a short synacthen test may be required.

Investigation of Cushing's. Normal results do not exclude Cushing's and a dexamethasone suppression test may be required.

Cortisol secretion is closely regulated by ACTH, which is secreted in an episodic manner superimposed on a circadian rhythm. Cortisol secretion occurs in parallel to the secretion of ACTH. Cortisol secretion is low in the evening and continues to decline into the first few hours of sleep, after which there is an increase. After waking, an individual’s cortisol secretion gradually declines throughout the day, with fewer secretory episodes of smaller magnitude. ACTH (and thus cortisol) secretion is stimulated by stress.

Please note that hydrocortisone, methylprednisolone, or prednisolone all cross-react with the cortisol assay.

Lab. Handling


Processing: Analysed from primary tube and stored at 4°C in the cold room (CB23)

Version 1.3 / February 2015                                                                                                         Approved by: Consultant Biochemist