False-negative aldosterone-to-renin ratio in a primary aldosteronism patient complicated with primary polydipsia: case report.

Aldosterone-to-renin ratio is the most reliable screening method of primary aldosteronism and has been widely used in clinical practice, but the index is influenced by many factors, some of which cause it false-negative, consequently leading to primary aldosteronism underdiagnosed. We report a rare case of a 27-year-old woman complaining of elevated arterial blood pressure and spontaneous hypokalemia but whose aldosterone-to-renin ratio were negative consecutively. She also had symptoms of polydipsia and polyuria for more than 20 years, with the volume of water intake and urine output up to 17 liters per day. Confirmatory tests of saline infusion test and captopril challenge test could not suppress plasma aldosterone concentration to the cutoff value. Abdominal contrast-enhanced CT suggested an adenoma on the right adrenal gland. After excluding other known causes of hypertension with hypokalemia, the patient was ultimately diagnosed with aldosterone-producing adenoma complicated with primary polydipsia. Complete clinical remission was achieved after unilateral adrenalectomy. The histopathology showed typical features of adrenocortical adenoma which was positive for CYP11B2 by immunohistochemistry, and next-generation sequencing results of tumor tissues revealed a missense mutation of the gene [chr11:128781619, c.451 (exon 2) G>A]. All these findings supported the diagnosis of aldosterone-producing adenoma. This study has shown that negative aldosterone-to-renin ratio screening result cannot simply exclude primary aldosteronism. Comprehensive patient's evaluation should be taken to avoid missed diagnosis in clinical work, especially for those who have potentially curative surgery.