Too Much of a Good Thing: A Woman with Hypertension and Hypokalemia

Abstract

A 64-year-old woman with a history of paranoid schizophrenia, hypertension, hyperlipidemia, and unexplained chronic hypokalemia presented in the outpatient psychiatric clinic for a routine follow-up visit with no specific complaints. Her history and review of systems revealed no remarkable findings. Her medications included an over-the-counter oral potassium supplement (equivalent to 2.5 mmol 3 times daily) and olanzapine (10 mg daily). She appeared well, and her physical exam was notable only for hypertension (188/105 mm Hg). A blood sample was obtained and blood chemistry tests were performed for routine monitoring. Laboratory evaluation showed concentrations within reference intervals for the patient’s serum sodium (142 mmol/L), urea nitrogen [2.9 mmol/L (8 mg/dL)], creatinine [53 μmol/L (0.6 mg/dL)], magnesium [1.0 mmol/L (2.4 mg/dL)], and glucose [5.2 mmol/L (94 mg/dL)]. Her total carbon dioxide was high at 43 mmol/L (reference interval 22–32 mmol/L), and her serum potassium was critically low at 1.9 mmol/L (reference interval 3.7–5.2 mmol/L). The critical potassium result was reported to the ordering physician, who arranged patient transport to the emergency department. In the emergency department, the patient was persistently hypertensive (170–180/95–110 mmHg). Review of the patient’s earlier records showed prior hypokalemia (2.1 and 3.3 mmol/L). Her electrocardiogram was normal. The patient reported no prescription diuretic use, laxative abuse, prolonged fasting, diarrhea, or vomiting. A repeat serum potassium measurement was 2.1 mmol/L, and at that time the patient’s serum osmolality was calculated to be 301 mOsm/kg. No arterial or venous blood gas measurements were performed. An untimed urine collection showed urine creatinine of 884 μmol/L (10 mg/dL), urine sodium 73 mmol/L, urine potassium 21 mmol/L, and urine osmolality 226 mOsm/kg. The primary abnormal findings were hypertension with concurrent hypokalemia and metabolic alkalosis. The patient was placed on continuous cardiac monitoring and given intravenous and oral potassium. Morning aldosterone [<0.06 nmol/L (<2.0 ng/dL)] …