A 55-year-old female presents with headaches and generalized weakness. Her mental status is intact. Her vital signs are blood pressure (BP) 170/80 mm Hg, HR 120/min, respiratory rate (RR) 18/min, and temperature 36.8°C.
What is the next best test to determine the cause of this acid-base abnormality?A. Serum cortisol
Correct Answer: B
The patient has a pH of 7.48, with a bicarbonate level of 34 mEq/L, suggesting metabolic alkalosis as the acid-base disorder. Hypokalemia is also noted with potassium of 3.1 mEq/L consistent with metabolic alkalosis. In differentiating the cause of metabolic alkalosis, urine chloride levels can be utilized. Urine chloride level less than 10 mmol/L suggests volume responsive or contraction alkalosis that can be corrected with saline replacement. Urine chloride greater than 20 mmol/L is associated with alkalosis that is resistant to volume expansion such as excess aldosterone, severe potassium deficiency, diuretic therapy, or Bartter syndrome. Metabolic alkalosis can be a feature of Cushing syndrome, but ordering a serum cortisol level would not be the first-line investigation (choice A). Liver function tests and serum ionized calcium are not typically useful for the investigation of metabolic acidosis (choices C and D).