A nurse is caring for a patient who has a new prescription for metformin. Which of the following laboratory tests should the nurse monitor? Which lab test should the nurse monitor for metformin?

The correct answer is D: Renal function tests. Metformin is primarily excreted by the kidneys, so monitoring renal function tests like serum creatinine and estimated glomerular filtration rate (eGFR) is crucial to assess kidney function and prevent potential metformin-induced lactic acidosis. Monitoring liver function tests (A) is not essential for metformin therapy, as metformin is not metabolized by the liver. Thyroid function tests (B) are not directly affected by metformin. Complete blood count (C) is not typically monitored specifically for metformin therapy. Therefore, the most appropriate choice is D as it directly reflects metformin's clearance and potential for toxicity.