Background: Primary aldosteronism (PA) is a common, curable and high-risk subset of hypertension, mandating detection. In all but the most severe cases, learned society guidelines recommend confirmatory testing. Whilst a variety of confirmatory tests exist, data describing their safety are limited. Concerns centre around the potential of some tests to precipitate hypokalaemia or a hypertensive emergency in a patient with PA on sub-optimal anti-hypertensive medication. In this study, we evaluated the intra-test effect on blood pressure and potassium of the two most widely used confirmatory tests for PA, the saline infusion test (SIT) and the captopril challenge test (CCT).
Methods: Retrospective analysis of patients being investigated for PA and who underwent either SIT or CCT between 2014 and 2021 at two tertiary centres in London. Identical protocols were used. Blood pressure was measured hourly from the start of each test. Serum potassium was measured at the start and end of each test.
Results: 96 SITs and 71 CCTs were performed in 159 patients (final diagnosis of PA in 115; 72.3%). The SIT was associated with a fall in serum potassium (mean change -0.18 mmol/l, P < 0.01) and rise in systolic blood pressure (median change +3 mmHg, P < 0.01). No episodes of hypertensive emergency were observed although one SIT was terminated due to hypertension. No alteration in either serum potassium or blood pressure was seen with the CCT.
Conclusions: The SIT, but not the CCT, was associated with a statistically significant decrease in serum potassium and increase in systolic blood pressure. Whilst this suggests that the CCT might be a more appropriate confirmatory test than the SIT in patients with problematic hypokalaemia or hypertension control (assuming equivalency of diagnostic performance), the absolute change in systolic blood pressure was small and test discontinuation was rarely required.
08 Nov 2021 - 10 Nov 2021