Impacts of the use of chemiluminescent enzyme immunoassay-measured plasma aldosterone concentration in the diagnostic process of unilateral primary aldosteronism: a real-world multicenter study in Japan

Unilateral primary aldosteronism (UPA) is characterized by a severe clinical phenotype and can be cured by adrenalectomy. Establishing accurate cutoff values that indicate the need for adrenal venous sampling (AVS) is crucial. Therefore, we aimed to identify appropriate cutoff values for screening and confirmatory testing to predict UPA by LC–MS/MS-equivalent plasma aldosterone concentration (PAC) using chemiluminescent enzyme immunoassay (CLEIA). A retrospective cohort analysis was conducted as part of the JPAS-II study of 443 patients diagnosed with PA using CLEIA-measured PAC, of whom 179 were confirmed by AVS as having UPA. The screening aldosterone-to-renin ratio (sARR), screening PAC, post-captopril challenge test (CCT) aldosterone-to-renin ratio (ARR), post-CCT PAC, and post-saline infusion test (SIT) PAC were significantly higher in patients with UPA than in those with bilateral PA (p 183 pg/mL/ng/mL/h (sensitivity of 0.95). The post-CCT ARR (AUC: 0.824 ± 0.022) and post-CCT PAC (AUC: 0.845 ± 0.021) were superior predictors of UPA to post-SIT PAC (AUC: 0.782 ± 0.037). When the cutoff values were designed to maximize sensitivity without a significant reduction in specificity, cutoff values for post-CCT ARR of >153 pg/mL/ng/mL/h (sensitivity: 0.85, specificity: 0.55) and for post-SIT PAC of >48 pg/mL (sensitivity: 0.80, specificity: 0.61) were obtained. Importantly, these cutoff values contributed to a diagnosis of UPA when the presence of hypokalemia or adrenal tumor was also considered. In conclusion, LC–MS/MS-equivalent CLEIA-measured cutoff values for post-CCT ARR of >153 pg/mL/ng/mL/h and for post-SIT PAC of >48 pg/mL are considered to indicate AVS. Study registration number: UMIN ID: 000046631.