Salivary Metabolite Could Replace Blood Tests in Cortisol Suppression Testing
A novel saliva-based marker for dexamethasone absorption may enable at-home Cushing's screening, cutting clinic visits.
Summary
The overnight dexamethasone suppression test is a standard tool for detecting abnormal cortisol production, but it typically requires a clinic blood draw the next morning. Researchers at Manchester University NHS Foundation Trust explored whether a dexamethasone metabolite found in saliva, called 11-dehydrodexamethasone, could serve as a reliable stand-in for blood dexamethasone measurement. Using a newly developed highly sensitive assay, they found that salivary 11-dehydrodexamethasone correlated reasonably well with blood dexamethasone levels, while dexamethasone itself measured directly in saliva performed poorly. This suggests patients could take the test drug at home, collect a morning saliva sample, and mail it to a lab, potentially streamlining diagnosis of conditions like Cushing's syndrome and adrenal tumors without requiring a hospital visit.
Detailed Summary
Accurate diagnosis of hypercortisolism — conditions involving excess cortisol, including Cushing's syndrome — relies heavily on the one-milligram overnight dexamethasone suppression test. In this test, a patient takes dexamethasone at bedtime and has blood drawn the following morning to check whether cortisol is appropriately suppressed. Measuring dexamethasone itself in that blood sample improves diagnostic accuracy by confirming the drug was actually absorbed. The problem is that this process requires a clinic visit, creating a burden for patients and healthcare systems alike.
Researchers at Manchester University NHS Foundation Trust set out to determine whether salivary sampling could replace blood sampling. They introduced the concept of measuring 11-dehydrodexamethasone — a metabolite produced when the salivary duct enzyme 11β-hydroxysteroid dehydrogenase type 2 converts dexamethasone — as a surrogate marker for drug absorption. Crucially, a parallel system already exists for cortisol: cortisone in saliva reflects serum cortisol well, a principle already used in home-based testing.
The team collected 90 paired blood and saliva samples the morning after the suppression test. Using liquid chromatography-tandem mass spectrometry, they measured serum cortisol, serum dexamethasone, and salivary cortisol, cortisone, dexamethasone, and 11-dehydrodexamethasone. Dexamethasone measured directly in saliva correlated very poorly with blood levels. However, salivary 11-dehydrodexamethasone showed a meaningful positive correlation with serum dexamethasone, achieving an R-squared of 0.75.
This finding opens the door to a fully home-based testing pathway. Patients could take dexamethasone at home, collect a morning saliva sample, and mail it for analysis — eliminating the need for clinic attendance while still capturing both cortisol suppression and drug absorption data.
Caveats include the fact that the correlation becomes less linear at higher dexamethasone concentrations, suggesting variability at the upper end. The study is based on the abstract only, limiting evaluation of full methodology, confounders, and clinical cutoff data needed for real-world implementation.
Key Findings
- Salivary 11-dehydrodexamethasone correlated with blood dexamethasone at R-squared 0.75, far better than direct salivary dexamethasone.
- Direct salivary dexamethasone measurement showed very poor correlation with serum levels (R-squared 0.135).
- A novel LC-MS/MS assay was developed to simultaneously measure four analytes in a single saliva sample.
- The approach could enable a fully at-home dexamethasone suppression test, removing the need for clinic blood draws.
- The salivary cortisol-to-cortisone relationship mirrored the dexamethasone-to-11-DHD relationship, validating the metabolite concept.
Methodology
Ninety paired serum and saliva samples were collected at 9 AM following the standard one-milligram overnight dexamethasone suppression test. Independent LC-MS/MS assays were used for serum analytes; a newly developed LC-MS/MS assay measured four salivary analytes simultaneously. Correlations were assessed using Pearson's R-squared.
Study Limitations
This summary is based on the abstract only, as the full paper is not open access, limiting assessment of statistical detail, patient demographics, and confounding factors. The serum DXM to salivary 11-DHD correlation becomes curvilinear and more variable at higher dexamethasone concentrations, which may affect reliability in some patients. The assay is novel and not yet validated in prospective clinical settings or across diverse populations.
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