Tezuka Y, et al. - In order to clarify the importance of clinical and pathological parameters of peripheral 18-oxocortisol (18oxoF) for the detection of aldosterone-producing adenoma (APA) in patients with primary aldosteronism, researchers analyzed 48 cases of APA, with the presence of KCNJ5 mutation in 35 cases. A wide range of peripheral 18oxoF concentration was detected, from 0.50 to 183.13 ng/dL. Findings revealed a positive correlation of peripheral 18oxoF level with intratumoral areas stained positively for steroidogenic enzymes. A functional deviation of aldosterone biosynthesis from the normal zona glomerulosa could be responsible for enhanced 18oxoF synthesis in APA, and the prevalence of KCNJ5 mutation in an APA could have an impact on the usefulness of peripheral 18oxoF measurement. These findings were generated for the first time in this investigation.