Screening for primary aldosteronism (PA) involves measuring the aldosterone-to-renin ratio (ARR). Cessation of interfering antihypertensive medications is recommended prior to screening to improve accuracy, but this adjustment is not always tolerated. The effects of these medications on ARR have not been studied in Australia. This study aims to evaluate the impact of different medications on ARR and determine optimal thresholds for PA screening.
We retrospectively identified patients referred to the Monash Health Endocrine Hypertension Service between July 2016 to December 2023 who had ARR measured on and subsequently off interfering medications (n=237). ARR above 70 was considered a positive screening result. Discordant results were negative ARR on interfering medications followed by positive ARR off interfering medications or vice versa.
Using confirmatory testing off interfering medications, 140 patients were diagnosed with PA, 79 did not have PA, and 18 had indeterminate diagnoses. 50/140 (36%) patients with PA had a false negative ARR on interfering medications, while 25/79 (32%) patients without PA had a false positive ARR. 41/48 (85%) patients taking beta blockers had a false positive ARR, while 21/55 (38%) on MRA, 11/42 (26%) on diuretics and 27/122 (22%) on ACE inhibitor or ARB had a false negative ARR. A lower ARR threshold of 20 pmol/mU had a sensitivity of 92% for PA, if measured on interfering medications. A plasma renin concentration (PRC) of < 10mU/L, off interfering medications, had a sensitivity of 90% for PA, while a PRC < 30 mU/L had a sensitivity of 94% for PA on interfering medications.
Beta-blockers and MRAs had the most significant impact on the ARR with increased false positive and false negative ARRs respectively. Revised ARR and PRC cutoffs can be utilised when screening patients on interfering hypertensives where medication switching is unfeasible.