8185 The diagnosis of primary aldosteronism: testing 2 screening approachesin a large reference laboratory population

Abstract Disclosure: M. Marcelli: Employee; Self; Quest Diagnostics. Stock Owner; Self; Quest Diagnostics. C. Bi: Employee; Self; Quest Diagnostics. J.W. Funder: None. M.J. McPhaul: Employee; Self; Quest Diagnostics. In many practices, the screening for primary aldosteronism (PA) relies on a single blood draw for plasma aldosterone concentration (PAC) and plasma renin activity (PRA) to establish an aldosterone-to-renin ratio (ARR). ARR cut-off levels vary between expert centers and between repeated assays in the same individual, emphasizing the potential variability of this screening approach. We conducted a study in 2 cohorts and used 2 screening approaches to identify probable PA (ARR ≥30 vs PRA suppressed to <1 ng/mL/h). Methods: Cohort A consisted of 94,829 consecutive paired PRA and PAC samples submitted by clinicians to evaluate the presence of PA. Cohort B is a subgroup of cohort A consisting of 27,893 patients in whom serum K was measured on the same day as PRA and PAC. Results: Based on ARR, 13.9% of cohort A (95%CI 13.6-14.1) and 13.9% of cohort B (95%CI 13.4-14.3) tested positive; based on PRA, 45.9% of cohort A (95%CI 45.5-46.2) and 45.2% of cohort B (95%CI 44.6-45.8) tested positive. A range of aldosterone levels was observed in cohort A vs B samples that screened positive using ARR vs PRA. PAC >15 ng/dL was present in a similar proportion of patients in both cohorts, regardless of the screening test used; however, PAC 5 to 15 and <5 ng/dL were present in higher proportions of patients positive for PRA than ARR in both cohorts A (25.2% vs 8.4% and 15.1% vs 0.7%) and B (26% vs 8.6% and 13.3% vs 0.5%), respectively. Hypokalemia was tested in cohort B and was more frequent than in an equal number of random controls not tested for the ARR test code (5.4% vs 1.8%) and when examining specific age groups (eg, age 50-70) in both women (4.9% vs 1.3%) and men (7.5% vs 1.5%). Conclusions•In both cohorts screened for PA, more individuals were identified by focusing on PRA < 1 than on ARR ≥ 30. This finding prompts a reassessment of the screening procedures for PA. •The proportion of positives for PA identified by the 2 screening tools was similar in cohort A vs B, suggesting that serum K should not be a routine test in the workup for PA.•Compared with the ARR test, Tthe PRA screening test identified more patients than the ARR test with PAC with 5 to 15 and <5 ng/dL in both cohorts A and B, while thethe tests identified a similar proportion of patients with PAC >15 ng/dL in both cohorts. This indicates that an ARR test of ≥30 is as effective as the PRA <1 for identifying florid cases of PA, but unlike PRA, is unable to identify less florid (and more common) cases of PA. •Hypokalemia was more frequent in cohort B than random controls, even after controlling for age (50-70) and sex, indicating that this cohort is enriched with a classic biochemical marker of PA. Presentation: 6/1/2024