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Test Code LAB1230014 Cortisol, Post Suppression (Dexamethasone Suppression Test)

Important Note

This test is used to measure cortisol levels after suppression with a dexamethasone supplement.

This test does not measure dexamethasone.

Useful For

  • The assessment of excess cortisol production
  • Normal individuals will show a marked decrease in plasma and urine free cortisol after administration of dexamethasone (dexamethasone suppression).  Patients with excess cortisol production will not.

Methodology

Electrochemiluminescence Immunoassay (ECLIA)

Performing Laboratory

Bozeman Health Laboratory Services

Specimen Requirements

Procedure:

Give patient 1 mg of dexamethasone orally at bedtime, between 8 p.m. and midnight.

 

Specimen Collection:

Specimen Type: Plasma or Serum
Container/Tube: Light-green top (lithium heparin gel), red top, or gold top
Specimen Volume: 1 mL

Specimen Minimum Volume: 0.5 mL

Collection Instructions:  Draw blood at 8 a.m. from a fasting patient.  Indicate time of draw on specimen.

Specimen Rejection:

  1. Hemolyzed samples may be rejected.
  2. 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.

Specimen Transport Temperature

Ambient <24 hours/Refrigerated >24 hours

Specimen Stability

Specimen Type Temperature Time
Plasma or Serum Ambient 24 hours
  Refrigerated 4 days
  Frozen 1 year

Reference Values

0.0-5.0 ug/dL

 

Normal patients suppress their plasma cortisol values to <5 µg/dL. Failure to suppress is characteristic of Cushings syndrome but also may be seen in patients with stress, endogenous depression, or phenobarbital or phenytoin therapy.

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding

82533