RATIONALE: Since the introduction of the aldosterone-to-renin ratio (ARR) as a screening tool for primary aldosteronism (PA), there has been a marked increase in the reported prevalence of this condition among hypertensive, even normotensive, subjects. PATIENT CONCERNS: But ARR as a spot blood draw for estimating a patient's aldosterone secretory status is influenced by many factors. DIAGNOSES: Here, we describe a series of patients with biochemically confirmed PA, whose diagnosis was delayed by the initial ARR assessment with non-suppressed renin. INTERVENTIONS: Patient 1 had a history of resistant hypertension for many years and had a negative initial screening for secondary hypertension (including ARR). At the reevaluation, ARR was close to cutoff still with normal renin after strict and extended drug washout, and the further workup for PA demonstrated a unilateral aldosterone producing adenoma that was surgically removed, with subsequent complete biochemical remission and partial clinical success. Patient 2 was diagnosed with idiopathic hyperaldosteronism combined with obstructive sleep apnea syndrome, which could increase renin resulting in a negative ARR, and finally got a better treatment effect with PA-specific spironolactone, as well as continuous positive airway pressure. Patient 3 with hypokalemia as the main presentation was finally diagnosed with PA after excluding other diseases, and proceeded to laparoscopic adrenalectomy and histologically confirmed an aldosterone producing adenoma. Postoperatively, patient 3 achieved complete biochemical success without any medicine. OUTCOMES: The clinical status of all three patients was effectively managed, resulting in either complete resolution or notable improvement of their respective conditions. LESSONS: After rigorous standardized diagnostic evaluation, there are still many reasons for ARR negative in PA, but they all basically occur in the background of normal or normal-high renin without suppression. A negative screening test result should be repeated and analyzed carefully if this is not consistent with the clinical picture. If, despite a repeatedly negative ARR, clinical suspicion remains high, we recommend consideration of further evaluation, including confirmatory tests and adrenal venous blood sampling (AVS) or even 68Ga-pentixafor PET/CT to better confirm the diagnosis and improve patient outcomes.