What is the procedure for cortisol level testing?

How to Draw a Cortisol Level

To properly assess cortisol levels, draw a morning serum cortisol sample between 7-9 AM, or perform a late-night salivary cortisol test, 24-hour urinary free cortisol collection, or overnight dexamethasone suppression test, depending on the clinical scenario. 1, 2

Morning Serum Cortisol Testing

Standard Procedure:

• Collect blood sample between 7:00-9:00 AM (when cortisol levels are at their peak)
• Patient should be fasting for at least 8 hours
• No special preparation of the venipuncture site is required
• Use standard venipuncture technique with appropriate collection tubes (typically red-top or gold-top serum separator tubes)
• Sample volume: 3-5 mL of whole blood is usually sufficient

Important Considerations:

• Morning cortisol values ≥300 nmol/L (≥10.8 μg/dL) generally exclude adrenal insufficiency 3
• Values <110 nmol/L (<4 μg/dL) suggest adrenal insufficiency 3
• Values between 110-300 nmol/L require further testing with stimulation tests 4, 3
• Immunoassays are commonly used but may lack specificity compared to LC-MS/MS 5

Alternative Cortisol Testing Methods

Late-Night Salivary Cortisol (LNSC):

• Collect saliva sample at bedtime (typically 11:00 PM) using a specialized collection device
• Patient should avoid eating, drinking, smoking, or brushing teeth for 30 minutes before collection
• Particularly useful for Cushing's syndrome screening 1, 6
• Advantages: non-invasive, reflects free (biologically active) cortisol, can be done at home

24-Hour Urinary Free Cortisol (UFC):

• Patient collects all urine over a 24-hour period in a specialized container
• Start collection after discarding the first morning void
• Include the first morning void of the following day
• Refrigerate sample during collection period
• Particularly useful when serum cortisol may be affected by altered binding protein levels 1, 2

Overnight Dexamethasone Suppression Test (DST):

• Patient takes 1 mg dexamethasone orally at 11:00 PM
• Blood sample drawn at 8:00 AM the following morning
• Normal response: cortisol <1.8 μg/dL (50 nmol/L) 1
• Useful for screening Cushing's syndrome

Special Situations

Pregnancy or Oral Contraceptive Use:

• Serum total cortisol may be elevated due to increased cortisol-binding globulin (CBG)
• Use UFC or salivary cortisol instead of serum total cortisol 2, 5

Critically Ill Patients:

• Interpretation of cortisol levels is challenging due to altered protein binding
• Consider using free cortisol measurements when available 5

Patients on Shift Work:

• LNSC testing should not be performed in patients with disrupted day/night cycles 1
• For these patients, serum cortisol should be drawn 30-60 minutes after waking

Cyclic Cushing's Syndrome:

• Multiple, periodic LNSC tests are particularly useful for longitudinal surveillance 1

Pitfalls to Avoid

• Collecting morning cortisol outside the 7-9 AM window (leads to falsely low values)
• Not accounting for medications that affect cortisol levels or dexamethasone metabolism
• Failing to consider altered binding protein states (pregnancy, liver disease, nephrotic syndrome)
• Using inappropriate reference ranges for the specific assay method
• Not considering diurnal variation when interpreting results

By following these guidelines, you can ensure accurate cortisol level assessment for proper diagnosis and management of adrenal disorders.