OR34-03 Variable and Pulsatile Circulating Aldosterone Levels in Primary Aldosteronism: Implications for Diagnosis and Sub-Type Differentiation

Introduction: Considerable intra-individual variability in circulating aldosterone levels has been observed in patients with primary aldosteronism (PA). The magnitude and implications of this phenomenon are not well characterized. Objective: To evaluate the acute variability in aldosterone in patients with confirmed PA. Methods: 373 patients with confirmed PA underwent adrenal venous sampling (AVS) after appropriate catheterization of bilateral adrenal veins. Peripheral venous aldosterone levels were measured 2 hours prior to AVS while in supine posture. After anesthesia induction with fentanyl and midazolam, AVS was performed while in the same supine posture, and aldosterone levels were drawn from the inferior vena cava (IVC) and in triplicate from the bilateral adrenal veins over 10 minutes. Differences between the pre-AVS and intra-AVS IVC aldosterone levels were analyzed, and regression models used to identify independent predictors of change. Coefficients of variation (COV) between triplicate aldosterone levels in each adrenal vein were calculated. Results: 81% of patients demonstrated a decrease in aldosterone concentration from pre-AVS to the intra-AVS IVC measurement. The mean decrease in aldosterone was 10.5 ng/dL (95% CI: 7.6–13.3) and the mean relative decrease in aldosterone was 39% (95% CI: 27–51%, P<0.0001). The absolute decrease in aldosterone was striking, with 48% of patients who had a decrease in aldosterone exhibiting an IVC aldosterone of less than or equal to 5 ng/dL. The absolute decrease in aldosterone was significantly associated with a higher aldosterone level (p<0.001) and lower systolic blood pressure at diagnosis (p=0.02). A wide variation in triplicate aldosterone values was seen in the span of 10-minute sampling, ranging from 1–300%, with COV of 21.0% in the left adrenal vein and 25.0% in the right adrenal vein. If the lowest of three aldosterone-to-cortisol (A/C) ratios on the dominant side and highest of three A/C ratios on the contralateral side were used instead of the average of the three values, the interpretation of the AVS would have changed from unilateral PA to bilateral PA in 15.9% of cases. Conclusions: These findings underscore the pulsatile and variable nature of circulating aldosterone levels in patients with bona fide PA. Aldosterone levels substantially declined in 81% of patients within a period of 2 hours while maintaining a fixed and supine posture. In half of these patients, aldosterone levels declined to 5 ng/dL or below, a threshold typically considered incompatible with PA. Further, adrenal venous aldosterone levels exhibited large variations on repeated sampling within a 10-minute span that could have influenced the interpretation of sub-type differentiation in nearly 16% of cases. Single circulating aldosterone values lack precision and reproducibility and may result in incorrect diagnosis and sub-type differentiation.