What is the protocol for an AM cortisol test?

Protocol for AM Cortisol Testing

The standard protocol for AM cortisol testing requires collecting a blood sample between 8:00-9:00 AM, when cortisol levels are naturally at their peak, with the patient in a fasting state and avoiding stress prior to collection. 1

Preparation Requirements

Patient Instructions

• Timing: Sample must be collected between 8:00-9:00 AM 1
• Fasting: Patient should be fasting prior to the test
• Medication considerations:
  • Hold medications that affect cortisol levels (if clinically safe)
  • Note any recent use of glucocorticoids, as these can suppress endogenous cortisol production
  • Document medications that may affect cortisol binding globulin (CBG) levels, such as oral estrogens 1

Pre-test Restrictions

• Avoid strenuous physical activity for at least 24 hours (ideally 48 hours) before testing 1
• Avoid mental stressors prior to testing, as these can elevate cortisol levels 1
• No alcohol consumption in the 12 hours before sampling 1
• Ensure adequate sleep the night before, as sleep disturbances can affect morning cortisol levels 1

Collection Procedure

1. Verify patient identity and confirm they have followed preparation instructions
2. Collect blood sample between 8:00-9:00 AM using standard venipuncture technique
3. Use appropriate collection tubes as specified by the laboratory (typically serum separator tubes)
4. Label specimens appropriately with patient information, date, and exact collection time
5. Process samples according to laboratory protocol (usually centrifugation within 1 hour)

Interpretation Guidelines

• Normal morning cortisol reference ranges vary by laboratory but typically fall between 5-25 μg/dL (138-690 nmol/L)
• A morning serum cortisol >300 nmol/L generally excludes adrenal insufficiency 2
• A morning serum cortisol <110 nmol/L suggests adrenal insufficiency 2
• Values between 110-300 nmol/L are indeterminate and require further testing 2

Common Pitfalls and Considerations

• Timing errors: Collection outside the 8:00-9:00 AM window can significantly affect results, as cortisol has a strong circadian rhythm 1
• Stress-induced elevation: Acute stress (including the stress of venipuncture) can falsely elevate cortisol levels
• Medication interference: Many medications can affect cortisol levels or testing, including exogenous steroids, certain antidepressants, and oral contraceptives 1
• Shift workers: Patients with disrupted sleep-wake cycles may have altered cortisol rhythms, making interpretation more challenging 1
• Cyclic Cushing's syndrome: Some patients may have intermittent cortisol excess, requiring multiple samplings over time 1

Follow-up Testing

If AM cortisol results are indeterminate (between 110-300 nmol/L), additional testing may be required:

• Low-dose dexamethasone suppression test
• ACTH stimulation test
• Late-night salivary cortisol
• 24-hour urinary free cortisol collection

For suspected Cushing's disease in children and adolescents, a more comprehensive protocol including multiple tests is recommended, as outlined in recent guidelines 1.

Remember that a single AM cortisol measurement provides a snapshot of adrenal function and may not fully characterize adrenal reserve, especially in critically ill patients who show significant hourly variability in cortisol levels 3.