Measurement of Late-Night Salivary Cortisol and Cortisone by LC-MS/MS to Assess Preanalytical Sample Contamination with Topical Hydrocortisone

To the Editor: Measurement of increased late-night salivary cortisol (LNSC)1 is now a mainstay in the diagnosis of endogenous Cushing syndrome (1). Patients typically sample their saliva at home and are carefully instructed to avoid using potential contaminants, such as topical creams or ointments containing hydrocortisone (authentic cortisol). Using these creams or ointments can cause preanalytical contamination of the saliva sample that cannot be distinguished from endogenous cortisol as measured by either immunoassay or liquid chromatography–tandem mass spectrometry (LC-MS/MS). With endogenous cortisol production, the cortisone concentration in the saliva is usually higher than the cortisol concentration, and typically the cortisol-to-cortisone ratio is <1, owing to the transfer of cortisone from the plasma and the conversion of cortisol to cortisone by 11-β-hydroxysteroid dehydrogenase type 2 (11-β-HSD2) in the salivary gland (2, 3). Contamination of the saliva with topical or oral hydrocortisone (cortisol) during sample collection would not be expected to increase salivary cortisone because there is no 11-β-HSD2 activity in collected saliva (3). Furthermore, topical hydrocortisone is usually not absorbed into the plasma compartment in substantial quantities. Therefore, topical hydrocortisone constitutes true contamination of the saliva and is not converted to cortisone. We hypothesized that a very high cortisol-to-cortisone ratio would be strong evidence that an increased salivary cortisol value was due to contamination with topical or oral hydrocortisone. Such a finding is prima facie evidence of contamination and is justification for the clinician to reinterview the patient.