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

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 <. 005) with estimated glomerular filtration rate (eGFR) (mL/min/1.73 m), with 95th percentile being 1.2 in controls, 3.0 in G2, 3.2 in G3a, 4.3 in G3b, 4.7 in G4, 5.7 in G5, and 7.1 in G5D. In the exploratory cohort, basal 8 Am cortisol and ACTH, and post-ONDST dexamethasone were similar among controls and CKD subgroups. ONDST ACTH (for evaluating the hypothalamo-pituitary-adrenal axis) was slightly higher in G5/5D vs controls (8.9 vs 6.1 pg/mL), while it was similar in G3b/G4 vs controls. Median 8 Am ONDST cortisol was similar on CLIA and LC-MS/MS in controls and higher on CLIA in G3b/4 (1.7 vs 1.1 μg/dL; P = .012) and G5/5D (2.4 vs 1.7 μg/dL; P = .002) than LC-MS/MS. Post-ONDST serum cortisol drop from 8 Am to 4 Pm was significant in controls (0.5-<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.