Final answer:
Liver enzymes should be monitored for a client taking isoniazid and rifampin, as both drugs can lead to hepatotoxicity and liver damage.
Step-by-step explanation:
The laboratory test a nurse should monitor for a client taking isoniazid and rifampin is the liver enzymes. Isoniazid and rifampin are antibiotics used in the treatment of tuberculosis and can be hepatotoxic, meaning they have the potential to damage the liver. Monitoring liver enzymes such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), which are included in a complete metabolic panel (CMP), can alert healthcare providers to any liver damage the medications might be causing. It's crucial to test these regularly since elevated levels may indicate liver dysfunction, requiring an adjustment to the treatment plan to prevent further damage.