What might be a key indicator to check before starting INH therapy?

Before initiating Isoniazid (INH) therapy, it is critical to assess liver function. INH is metabolized by the liver, and one of the important considerations for therapy is the potential for hepatotoxicity, which can lead to liver damage. Monitoring liver function tests (LFTs) helps to ensure that the patient has adequate hepatic function to safely process the medication and to identify any pre-existing liver conditions that could be exacerbated by the treatment.

Liver function is particularly essential to evaluate because patients with compromised liver function may have an increased risk of developing serious side effects. Understanding the patient's liver health at the outset allows for informed clinical decisions regarding the initiation of therapy and the management of potential adverse reactions throughout the treatment course.

Other factors, such as body mass index or blood pressure levels, may be relevant for a patient's overall health but do not specifically influence the safety profile of INH the way liver function does. Similarly, while prior tuberculosis treatment might inform the clinical approach, it does not directly affect the initiation of INH therapy in regards to the risk of hepatotoxicity.