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Different methods to estimate serum free cortisol: a comparison during cortisol tetracosactide testing
Clinical Chemistry and Laboratory Medicine
|November 11, 2014
Summary
Saliva and ultrafiltration methods for serum free cortisol (FC) estimation are convenient and correlate well with total cortisol (TC) during ACTH testing, suggesting their utility as surrogate assays.
Area of Science:
- Endocrinology
- Clinical Chemistry
Background:
- Serum cortisol is routinely measured by immunoassays.
- Serum free cortisol (FC) is a better survival indicator than total cortisol (TC) in intensive care units.
- Various methods exist to estimate FC, including saliva sampling.
Purpose of the Study:
- To compare five different methods for estimating FC.
- To evaluate FC estimation before and after an ACTH stimulation test.
- To assess methods in patients suspected of adrenal insufficiency.
Main Methods:
- Collected serum and saliva from 130 patients before and after tetracosactide injection.
- Estimated FC using serum ultrafiltration, quadratic/cubic equations, TC/cortisol-binding globulin ratio, and saliva cortisol.
- Determined total cortisol (TC) for comparison.
Main Results:
- FC concentrations from different techniques were significantly correlated.
- Saliva FC (salFC) and ultrafiltration FC (filtFC) showed good linearity with other methods.
- salFC and filtFC, along with cubic FC (cubFC), demonstrated the best ROC curves post-ACTH test.
Conclusions:
- Different FC estimation techniques show significant but not identical correlations with TC.
- salFC and filtFC are more convenient than cortisol-binding globulin assays.
- salFC and filtFC are preferred surrogate assays due to better correlation with TC during ACTH tests.
