Effect of a Prior Two-Hour Postural Test on Seated Saline Suppression Test Results in Patients Predominantly Evaluated for Adrenal Incidentalomas

Background/Objectives: The Seated Saline Suppression Test (SSST) is widely used for investigation of primary hyperaldosteronism (PA); however, the impact of a one-hour sitting period prior to SSST (as recommended by the Endocrine Society, with a 7.8 ng/dL aldosterone cut-off) on the test outcome remains unclear. Methods: In 82 individuals (23 males) aged 57.3 ± 12.6 years, BMI 27.1 ± 5.1 kg/m2, where the majority were diagnosed with adrenal incidentalomas (n = 75), we performed an SSST preceded by a 120 min postural test (first protocol), or immediately after waking (second protocol, a cross-over design). Results: Though aldosterone and renin concentrations before the onset of SSST were higher after the first protocol (p < 0.001), an overall suppression of aldosterone was not different after the first versus the second protocol (6.34 ± 0.68 ng/dL (mean ± SEM) versus 5.74 ± 0.66 ng/dL, p = 0.124). There was no significant difference between the number of individuals with aldosterone > 10 ng/dL, i.e., nine (11%) for the first protocol versus eight (9.75%) for the second protocol, p = 1.00, and for the “grey zone” aldosterone of 7.8–10 ng/mL after SSST (five (6.1%) in each group, p = 1.0). Aldosterone-to-direct-renin ratio (ADR ratio) was higher in those who failed to suppress aldosterone (p < 0.001) but offered a poor prediction of SSST outcome with the lowest ADR ratio of 0.398 ng/dL/µIU/mL in those with aldosterone > 7.8 ng/dL, and the highest ADR ratio of 26.04 ng/dL/µIU/mL for those with aldosterone < 7.8 ng/dL on SSST. Conclusions: Two-hour postural test before SSST does not significantly impact aldosterone suppression after saline infusion, while the ADR ratio does not fully discriminate between those who suppress and those who do not suppress aldosterone secretion on SSST, at least in those with adrenal incidentalomas.