The patient with tuberculosis is now on isoniazid (INH). Which laboratory test should the nurse monitor?

A. Liver enzymes/ LFTs: Correct. Isoniazid (INH) is hepatotoxic and can cause liver damage. Monitoring liver function tests (LFTs) helps detect hepatotoxicity early. B. PT and PTT: These tests measure blood clotting and are not directly affected by INH. C. BUN: Blood Urea Nitrogen (BUN) measures kidney function, and while it is important, INH primarily affects the liver. D. CBC: Complete Blood Count (CBC) is useful for overall health but not specifically for monitoring INH therapy.