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Test Code LAB4954 Dexamethasone Suppression Reflex

Performing Laboratory

Barnes-Jewish Hospital Laboratory

Methodology

Electrochemiluminescence Immunoassay (ECLIA)

Literature References:

1. Package insert: Cortisol II Roche Corporation 05/2021

 

 

Specimen Requirements

Specimen Type: Plasma and Serum

Container/Tube: Mint green top (lithium heparin) and Red top tube

Specimen Volume: Full tube

Collection Instructions:

1. Give patient 1 mg of dexamethasone by mouth between 2300 and 2400.

2. Draw specimen at 0800.

Additional Information:

1. Prednisolone can interfere with this assay by causing a false-positive reaction.

2. Test performed is Cortisol, Plasma.

Day(s) Test Set Up

Monday through Sunday

 

Turnaround Time:
Routine: 4 hours after receipt in laboratory

If Cortisol is ≥1.8 ug/dL, Dexamethasone will be sent to Esoterix Endocrinology Lab. 

Test Classification and CPT Coding

82533 and 80375 

Reference Values

Normal cortisol suppression with overnight Dexamethasone is <1.8 mcg/dl
An abnormal test does not establish a diagnosis of Cushing’s syndrome.

In conditions with elevated levels of cortisol binding globulin (pregnancy, estrogen therapy, hyperthyroidism), a false-positive test is likely and use of another screening test (eg, LAB382 Cortisol/Cortisone, Free, Urine) is preferable.

A false-positive test may occur because of:

1. Low dexamethasone levels—noncompliance or increased metabolism of dexamethasone (eg, phenytoin, phenobarbital)

2. Interference with cortisol assay (eg, prednisone)

3. Temporary loss of suppressibility (eg, depression, alcoholism)

Specimen Transport Temperature

Ambient

Additional Information

For BJH Laboratory Use Only
Alternate Tube:

Red-top tube

Dark green tube (Li Hep)

Purple top (K2 & K3 EDTA)

Separator gel tube is acceptable

Analyte Stability:

See Analyte Stability Chart in Special Instructions.

Laboratory Processing Instructions:

Test performed in BJH Core Lab. Test performed is Cortisol, Plasma.  Processed by automated line for delivery to the Cobas 8000.  Completed specimens are stored refrigerated for 5 days.

Special Instructions