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Test Code CORTO Cortisol, Free and Total, Serum

Advisory Information

For confirming the presence of synthetic steroids, order SGSS / Synthetic Glucocorticoid Screen, Serum.


Cushing syndrome is characterized by increased serum cortisol levels. However, the 24-hour urinary free cortisol excretion is the preferred screening test for Cushing syndrome, specifically CORTU / Cortisol, Free, 24 Hour, Urine that utilizes liquid chromatography-tandem mass spectrometry. A normal result makes the diagnosis unlikely.


The most common cause of increased plasma cortisol levels in women is a high circulating concentration of estrogen (ie, estrogen therapy, pregnancy) resulting in increased concentration of corticosteroid-binding globulin. This does not result in an increase in the free, bioactive cortisol fraction. For this reason, measurement of 24-hour urinary free cortisol (CORTU / Cortisol, Free, 24 Hour, Urine) or demonstration of absent diurnal variation (ie, by midnight salivary cortisol measurement SALCT / Cortisol, Saliva) are the preferred means of diagnosing spontaneous Cushing syndrome.


This test is not recommended for evaluating response to metyrapone; DCORT / 11-Deoxycortisol, Serum is more reliable.


A low plasma cortisol level does not give conclusive indication of congenital adrenal hyperplasia. DCORT / 11-Deoxycortisol, Serum; OHPG / 17-Hydroxyprogesterone, Serum; and DHEA_ / Dehydroepiandrosterone (DHEA), Serum provide a more accurate and specific determination of the enzyme deficiency.

Additional Testing Requirements

If multiple specimens are drawn, send separate order for each specimen.

Necessary Information

Include time of draw.

Specimen Required

Container/Tube: Red top

Specimen Volume: 1.85 mL

Collection Instructions: Morning (8 a.m.) specimens are preferred. The 8 a.m. cortisol can be referred to as the a.m. cortisol and can be drawn anywhere between 6 a.m. and 10:30 a.m. in the morning.

Useful For

Assessment of cortisol status in cases where there is known or a suspected abnormality in cortisol-binding proteins or albumin


Assessment of adrenal function in the critically ill or stressed patient, thus preventing unnecessary use of glucocorticoid therapy


Second-order testing when cortisol measurement by immunoassay (eg, CORT / Cortisol, Serum) gives results that are not consistent with clinical symptoms, or if patients are known to, or suspected of, taking exogenous synthetic steroids


An adjunct in the differential diagnosis of primary and secondary adrenal insufficiency


An adjunct in the differential diagnosis of Cushing syndrome

Profile Information

Test ID Reporting Name Available Separately Always Performed
CINP Cortisol, S, LC-MS/MS Yes Yes
CORTF Cortisol, Free, S Yes Yes

Special Instructions

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

Cortisol, Free and Total, S

Specimen Type

Serum Red

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Refrigerated (preferred) 28 days
  Ambient  28 days
  Frozen  28 days

Reject Due To


Mild OK; Gross reject


Mild OK; Gross OK


Mild OK; Gross reject



Reference Values


6-10:30 a.m. Collection: 0.121-1.065 mcg/dL



p.m.: 2-14 mcg/dL

Day(s) and Time(s) Performed

See Individual Unit Codes

Analytic Time

3 days

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information



LOINC Code Information

Test ID Test Order Name Order LOINC Value
CORTO Cortisol, Free and Total, S In Process


Result ID Test Result Name Result LOINC Value
84279 Cortisol, S, LC-MS/MS 2143-6
65423 Cortisol, Free, S 2145-1
23606 AM Cortisol 9813-7
23607 PM Cortisol 9812-9