How to manage cross-reactivity with 11-deoxycortisol in cortisol measurement?

Managing Cross-Reactivity with 11-Deoxycortisol in Cortisol Measurement

To manage cross-reactivity with 11-deoxycortisol in cortisol measurement, use liquid chromatography-tandem mass spectrometry (LC-MS/MS) instead of immunoassays, especially when patients are taking medications like metyrapone, osilodrostat, or mitotane that increase 11-deoxycortisol levels. 1, 2

Why Cross-Reactivity Occurs

Cross-reactivity with 11-deoxycortisol is a significant issue when measuring cortisol levels in patients:

• It occurs primarily with cortisol immunoassays due to structural similarities between cortisol and 11-deoxycortisol
• Several medications used to treat Cushing's syndrome significantly increase this problem:
  • Metyrapone (11β-hydroxylase inhibitor) - causes rapid accumulation of 11-deoxycortisol 1
  • Osilodrostat (11β-hydroxylase inhibitor) - specifically noted to cause cross-reaction in routine assays 1
  • Mitotane - also causes cross-reaction with 11-deoxycortisol in routine assays 1

Recommended Testing Approaches

1. Use Mass Spectrometry-Based Methods

• First-line recommendation: LC-MS/MS - This technique provides superior specificity by identifying cortisol based on its exact molecular mass 3, 4
  • Eliminates cross-reactivity issues with 11-deoxycortisol
  • Offers high sensitivity with limits of quantification as low as 0.6 nmol/L for free cortisol 4
  • Provides accurate mass identification with mass accuracy <2.5 ppm 3

2. When Using Immunoassays (if LC-MS/MS unavailable)

• Be aware that prednisolone, 17-hydroxyprogesterone, and 11-deoxycortisol show statistically significant cross-reactivity in immunoassays 5
• Interpret results cautiously, especially in patients taking medications that increase 11-deoxycortisol levels
• Consider that cortisol values obtained by immunoassay may be falsely elevated compared to chromatographic methods 6

Specific Recommendations by Clinical Scenario

For Patients on Metyrapone

• Metyrapone causes rapid UFC decrease (typically in first month) but creates significant 11-deoxycortisol accumulation 1
• Always use LC-MS/MS for cortisol measurement in these patients
• If using immunoassays, be aware that cortisol levels may appear falsely elevated due to cross-reactivity 1

For Patients on Osilodrostat

• Osilodrostat is FDA-approved for CD patients when pituitary surgery isn't an option 1
• It specifically causes cross-reaction with 11-deoxycortisol in routine assays 1
• Use LC-MS/MS to avoid false cortisol readings

For Patients on Mitotane

• Mitotane is FDA and EMA approved for adrenal cancer with endogenous Cushing's syndrome 1
• It also causes cross-reaction with 11-deoxycortisol in routine assays 1
• Use LC-MS/MS for accurate cortisol assessment

Sample Collection Considerations

• For 24-hour urinary free cortisol (UFC) collections:

  • Patients should avoid strenuous physical activity for at least 24-48 hours before and during collection 2
  • Collect at least 2-3 samples to account for variability 2
  • Be aware that urine volume and glomerular filtration rate strongly predict UFC levels 1

• For late-night salivary cortisol (LNSC):

  • Multiple collections (≥2) on consecutive days improve diagnostic accuracy 1, 2
  • LC-MS/MS measurement of salivary cortisol eliminates cross-reactivity concerns 7

Key Pitfalls to Avoid

• Don't rely solely on immunoassays when monitoring patients on medications that increase 11-deoxycortisol levels
• Don't interpret cortisol levels in isolation - consider the medication history and potential for cross-reactivity
• Don't assume cortisol assays are equivalent - LC-MS/MS values may be lower than immunoassay values due to the latter's lack of specificity 6
• Don't overlook the exponential relationship between serum and salivary cortisol - this reflects CBG binding capacity saturation 7

By implementing these recommendations, clinicians can accurately assess cortisol levels in patients with potential 11-deoxycortisol cross-reactivity, ensuring appropriate diagnosis and management of conditions like Cushing's syndrome.