1. Presented by Curtis Gravenmier, MD and reviewed by Claire Knezevic, PhD.

An elderly patient with leukemia, essential hypertension, and hypothyroidism is admitted to the hospital due to severe deconditioning. The patient denies fever, chills, diarrhea, and vomiting. The patient's routine medications include lisinopril, rosuvastatin, and levothyroxine. The patient is also receiving chemotherapy for leukemia, as well as acyclovir, levofloxacin, and posaconazole for antimicrobial prophylaxis.

Initial vital signs are BP 208/93, HR 59, RR 20, and T 36.9 C. Laboratory studies are remarkable for serum potassium of 2.6 mmol/L, low plasma renin activity, and serum aldosterone less than 1 ng/dL (reference range ? 28 ng/dL). Posaconazole is discontinued, resulting in correction of both hypertension and hypokalemia.

Question:
Which of the following tests could be used to further investigate suspected non-aldosterone mineralocorticoid activity?