(CSEMP076) COMPARISON OF THE EQUIVALENCE OF INTRAVENOUS AND ORAL SODIUM OVERLOADS FOR THE DIAGNOSIS OF PRIMARY ALDOSTERONISM : PRELIMINARY RESULTS

Abstract:

Introduction: Primary aldosteronism (PA) is the most common cause of secondary hypertension and is currently underdiagnosed. Consequently, it represents a significant cause of mortality and increased morbidity among hypertensive patients, which could potentially be prevented. Salt Infusion test (SIT) and oral salt loading (OSLT) are two recommended methods to confirm the diagnosis of PA, according to the "Endocrine Society Clinical Practice Guideline." However, several studies have reported divergent results regarding their performance, with insufficient evidence to definitively favor one approach. Also, up to now, no study compares the diagnostic performance of those two.

Method: Our retrospective study include hypertensive patients assessed by the Endocrinology Department of CIUSSS-de-l'Estrie-CHUS, who had a positive RRA (renin-to-aldosterone ratio) screening test (N 79) between 2015 and 2023. These patients subsequently underwent both SIT and OSLT, and we directly compared the rates of positivity. The standard positive threshold for the SIT was an aldosterone of 163 pmol/L at the end of the 4h of salt infusion. For the OSLT the standard threshold for a positive test was a 24h urinary aldosterone of 33 pmol with a 24h urinary sodium excretion of 170mEq or more. An intermediate threshold of 27 pmol was also considered. We compared the rate of positivity for both threshold for the SIT compared to the OSLT.

Results: Up to now, among the 79 included patients, 49 had at least one positive diagnostic test using the standard threshold (28 with SIT and 35 with OSLT). When using the intermediate threshold for the OSLT, 45 were positive. Comparing positive cases between SIT and OSLT, we found that the average screening RRA was significantly higher in cases detected by the intravenous method than the oral one, 268.89 vs. 193.50 (p = 0.025). Using standard threshold, the SIT and OSLT were concordant in 73.4% (95% CI: 62.8-81.9) of cases. When using intermediate threshold, they were concordant in 68.4% (95% CI: 57.5-77.6). The McNemar test suggests that the OSLT with an intermediate threshold is not equivalent to the SIT (p < 0.001), while there is no significant difference with the standard threshold (p=0.189).

Discussion: These results suggest that OSLT using an intermediate might be more sensitive to confirm PA than SIT, likely due to an increased detection of milder cases. We also think it is explained by the integration of all the aberrant stimuli that regulate aldosterone in PA over a day instead of 4 hours during SIT.