The ratio of aldosterone-to-renin activity is currently recommended as a screening test for primary aldosteronism (PA). There are many factors interfering the interpretation of aldosterone-renin ratio (ARR) and could hamper in-time diagnosis of PA. Here, we first report a patient with underlying Page phenomenon and an accidentally disclosed adrenal incidentaloma. High renin secretion from Page phenomenon had masked higher ARR into normal ARR obscuring the diagnosis of PA. However, adrenal venous sampling (AVS) confirmed the autonomous aldosterone secretion with left adrenal vein plasma aldosterone concentration (PAC) 124.1 ng/dl and a lateralization ratio 3.3. AVS may discriminate masked PA due to high renin secretion from Page kidney. It is suggested that clinicians should cautiously interpret aldosterone-renin ratio and consider diagnostic AVS if hyperaldosteronism is highly suspected especially in the background of other secondary hypertension.