Overnight 1-mg DST Serum Cortisol in Various Stages of Chronic Kidney Disease - Normative Data and Underlying Mechanisms

Abstract

Context: Data on the overnight 1 mg-dexamethasone suppression test (ONDST) in renal dysfunction are limited. Objective: We aim to determine the normative range of ONDST cortisol across chronic kidney disease (CKD) stages and reasons for its alteration. Methods: Prospectively, 180 CKD (30 each in G2-G5/5D) patients and 30 healthy controls underwent ONDST 8 Am serum cortisol (chemiluminescent immunoassay [CLIA]). In an exploratory cohort, 45 (15 each: G3b/G4, G5/G5D, and healthy controls) individuals' blood biochemistry for basal (8 Am) cortisol and adrenocorticotropin (ACTH), post-ONDST 8 Am dexamethasone, ACTH, cortisol (CLIA and liquid chromatography-tandem mass spectrometry), and 4 Pm cortisol was collected. Results: Post-ONDST cortisol (μg/dL) correlated inversely (r = 0.47; P <0.2 μg/dL) and G3b/4 (1.7-1.2 μg/dL), but not in G5/5D (2.4-2.2 μg/dL). Conclusion: The normative data of ONDST serum cortisol with eGFR-based cutoffs are useful in evaluating Cushing syndrome in CKD. Prolonged cortisol half-life and immunoassay-related assay cross-reaction are likely contributors to higher ONDST cortisol.