Which monitoring is essential when initiating a mineralocorticoid receptor antagonist in HFrEF?

• A. Potassium and creatinine
• B. Sodium and chloride
• C. Glucose and HbA1c
• D. Calcium and phosphate

Answer: (A)

Monitoring potassium and kidney function is essential when starting a mineralocorticoid receptor antagonist in HFrEF. These drugs block aldosterone, which normally promotes potassium excretion in the distal nephron. By reducing aldosterone activity, they can cause potassium to accumulate, raising the risk of hyperkalemia, especially in patients with borderline kidney function or those taking other potassium-increasing medications. They can also affect renal function, so serum creatinine (or eGFR) must be tracked to detect any decline in filtration capacity. Baseline values are important, and you should recheck potassium and creatinine soon after initiating therapy and again with any dose change, then at regular intervals to ensure safety while continuing the mortality and morbidity benefits of therapy. Other lab checks (like sodium, chloride, glucose/HbA1c, or calcium/phosphate) are not the primary safety focus for MRAs in this context.