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Laboratory: Clinical Biochemistry  (AUTOMATED)
Test Name:
CORTISOL - (P) (S)
Test Code: COR
Clinical Information:
Description: Plasma cortisol testing is used to screen and diagnose primary and secondary adrenal insufficiency, as well as in differential diagnosis of Cushing syndrome.
Patient Preparation InstructionsDiscontinue high dose biotin (and multivitamins) at least 8 hours prior to blood collection.
Collection Devices:
Specimen Required:


Plasma: 2.0 mL
Pediatric Plasma: 0.2 mL

Collection Information: 

1. Draw blood at indicated time:

·       AM cortisol specimens should be collected at 0700 - 0900h

·       PM cortisol specimens should be collected at 1500 - 1700h

·       All other collection times are considered random.

2. Centrifuge plasma/serum within one hour of collection.

3. Aliquot (if not tested onsite)

Specimen Stability:

Ambient: 24 hours

Refrigerated: 4 days

Frozen: 12 months, freeze only once

Referral:
Serum: 2.0 mL

Shipping & Storage: Store and ship refrigerated or frozen. Avoid repeated freeze-thaw cycles (#110-10-05 Serum / Plasma Separation Procedure & Transport)
Requisition:
Reference Values:
AgeTimeReference Interval
< 8 daysRandom55-304 nmol/L
8 d - <12 mRandom77 – 635 nmol/L
12 m - <16 yRandom80 – 580 nmol/L
³ 16 y7-9 AM140 – 690 nmol/L
3-5 PM80 – 440 nmol/L
Random80 – 690 nmol/L

Plasma cortisol levels are normally highest around 8 am and lowest around 12 am.

 

Comment added to inpatient results: “Plasma cortisol can’t be interpreted in the context of exogenous steroids, estrogens, and critically ill patients. Clinical correlation is strongly urged.”

 

Method of Analysis: Competitive ECLIA Roche immunoassay

 

Availability:
Daily
See Also:
More Information:
Interpretation & Assay Interferences: Multivitamins (45–125 µg biotin) or biotin-only supplements up to 1 mg per day do not interfere with cortisol assay. Samples should not be taken from patients receiving therapy with high biotin doses (i.e. >5 mg/day) until at least 8 hours after the last dose.

Oral contraceptives, pregnancy, or estrogen therapy cause elevated plasma cortisol levels due to an increase in binding proteins.

Prednisolone, 6-α-methylprednisolone, or prednisone treatment may cause falsely elevated cortisol results.

During metyrapone tests, 11-deoxycortisol levels are elevated. Falsely elevated cortisol values may be determined due to cross reactivity of the assay with 11-deoxycortisol. 

Patients suffering from 21-hydroxylase deficiency exhibit elevated 21-deoxycortisol levels and this can cause falsely elevated cortisol results.