SUN-478 Assessment Of Cortisol And Dexamethasone Concentrations In Capillary Blood

Abstract Disclosure: C.A. Villavicencio Torres: None. S. Ahmadian: None. K. Moehnke: None. V.M. Fell: None. R.L. Taylor: None. S.K. Grebe: None. A.D. Maus: None. I. Bancos: None. Background: Evaluation of adrenal disorders relies on total cortisol measurements at baseline or during dynamic testing. Accurate cortisol assessment that avoids phlebotomy may simplify the work up of adrenal disorders, decrease healthcare costs, and improve patient experience. Objectives: We aimed to compare cortisol and dexamethasone concentrations between venipuncture-based (clinical) and capillary blood samples. Methodology: We conducted a cross-sectional study (July 2024-April 2025) of adults undergoing standard-of-care cortisol measurements. Capillary blood samples were collected alongside clinical samples. Capillary measurements included total cortisol and dexamethasone (mass spectrometry). Clinical samples were tested for total cortisol (Roche immunoassay) and dexamethasone (mass spectrometry). Results: Of 318 patients (243, 77% women, median age 53 years, IQR 39-66), 227 (71%) underwent dexamethasone suppression test (DST) and 88 (28%) cosyntropin stimulation test (CST). Capillary blood collection failed in 13 (4%) patients. In patients undergoing DST, median post-dexamethasone serum cortisol was 1.3 mcg/dL (IQR 0.8-2.2), and serum dexamethasone was 0.41 mcg/dL (IQR 0.27-0.59), while median capillary cortisol was 1.5 mcg/dL (IQR 1-2.5), and capillary dexamethasone was 0.33 mcg/dL (IQR 0.21-0.51). Capillary cortisol (r=0.95, 95% CI [0.93, 0.96], p<.0001) and capillary dexamethasone (r=0.93, 95% CI [0.90, 0.95], p<.0001) showed strong correlation with their respective clinical measurements. In patients undergoing CST, median baseline serum cortisol was 7.5 mcg/dL (IQR 5-10), and median baseline capillary cortisol was 8.5 mcg/dL (IQR 6-12). Median post-CST 60-minute serum cortisol was 23 mcg/dL (IQR 20-25), while capillary cortisol was 25 mcg/dL (IQR 21-28). Baseline (r=0.77, 95% CI [0.66, 0.85], p<.0001) and post-CST 60-minute capillary cortisol (r=0.88, 95% CI [0.81-92], p<.0001) strongly correlated with clinical measurements. Post-dexamethasone cortisol in paired DST samples showed that capillary measurements were higher than serum cortisol (median difference 0.20 mcg/dL (95% CI [0.12, 0.42], p<.0001), while paired capillary dexamethasone concentrations were lower than serum dexamethasone concentrations (median difference 0.04 mcg/dL (95% CI [0.03, 0.07], p<.0001). In CST, paired baseline capillary and serum cortisol concentrations were similar (median difference 0.10 mcg/dL, 95% CI [0.3, 0.3], p=.3660), while paired post-CST 60-minute capillary cortisol was higher than serum cortisol by a median of 2.8 mcg/dL (95% CI [2, 3.2], p<.0001). Conclusion: Capillary cortisol and dexamethasone concentrations demonstrate excellent correlation with venipuncture-based measurements. Following validation with at-home collection, capillary blood measurements may serve as an alternative for evaluating adrenal disorders. Presentation: Sunday, July 13, 2025