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Cosyntropin (ACTH) Stimulation - Cortisol Blood Level

Dexamethasone Suppression Test - Overnight, Serum Cortisol, Dexamethasone Suppression of Cortisol Test, Overnight, DEXSO, DEXCO

Test Codes

EPIC: LAB1230313

Department

Chemistry

Instructions

Specimen should be drawn between 7:00 am and 8:00 am following oral intake of 1.0 mg dexamethasone between 11:00 pm and midnight the night before.

NOTE: The physician ordering the test MUST prescribe the 1.0 mg dexamethasone tablet. This is not supplied by the Lab. 

Specimen Collection Criteria

Collect: One Gold-top SST tube. (Minimum Whole Blood: 4.0 mL)

Contact the Laboratory for acceptability of other tube types.

Physician Office/Draw Specimen Preparation

Let SST specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged SST tube within two hours of collection.

Preparation for Courier Transport

Transport: Centrifuged SST tube refrigerated (2-8°C or 36-46°F). (Minimum: 1.0 mL)

Rejection Criteria

Specimens not collected and processed as indicated. Consult a pathologist prior to specimen rejection or test cancellation for any timed tests.

In-Lab Processing

Let SST specimens clot 30-60 minutes. Centrifuge SST tubes or Microtainers^® to separate serum from cells. Deliver immediately to the appropriate testing station.

Storage

Specimen Stability for Testing:

Centrifuged SST Tubes and Microtainers^® with Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 8 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): Unacceptable

Red-top Tubes and Microtainers^® without Separator Gel
Room Temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Serum Specimens (Pour-Overs)
Room Temperature (20-26°C or 68-78.8°F): 8 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 7 days

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 5 days

Laboratory

Dearborn Chemistry Laboratory
Royal Oak Automated Chemistry Laboratory
Troy Chemistry Laboratory

Performed

Monday – Saturday.
Results and interpretation within 48 hours of receipt in the Laboratory.

Reference Range

Normal Dexamethasone Suppression Test: Serum Cortisol is suppressed to a value of less than 1.8 mcg/dL.

Test Methodology

Chemiluminescent Immunoassay for Cortisol.

The patient ingests 1.0 mg dexamethasone at between 11:00 pm and midnight. A blood sample is collected the following morning between 7:00 am and 8:00 am. 

Interpretation

If the cortisol level does not suppress, the patient should be investigated further. If the AM serum cortisol is less than 1.8 mcg/dL the patient most likely has a normally suppressible pituitary-adrenal axis. However, this test should not be used as the sole criterion to rule out Cushing syndrome. Additional investigations include 24-Hour Urine Free Cortisol or Salivary Cortisol (collected at midnight).

It should be noted that one percent of normal individuals, 13% of obese, about 25% of hospitalized or chronically ill patients, and women with increased cortisol binding proteins due to increased estrogens (e.g. pregnancy) give a false positive result. Less than 2% of false negative values are expected. Additional testing would include 24-Hour Urine Free Cortisol, Salivary Cortisol, and/or a 2-Day, Low Dose Dexamethasone Suppression Test.

Interference: 11-deoxycortisol (arising from metyrapone treatment) and cortisone have cross reactivities of 7.3 and 7.4 respectively. Prednisolone, 6-methyl-presnisolone and prednisone have cross reactivities of 27.0, 20.9, and 6.6% respectively.

Clinical Utility

This assay should be used as a screen for Cushing's syndrome. If positive, follow-up investigations are necessary to confirm.

CPT Codes

82533

Contacts

Last Updated

4/24/2025