**Core Concept**
Infliximab is a monoclonal antibody against tumor necrosis factor-alpha (TNF-alpha), used in the treatment of rheumatoid arthritis and other inflammatory conditions. TNF-alpha plays a crucial role in systemic inflammation and is involved in the pathogenesis of rheumatoid arthritis.

**Why the Correct Answer is Right**
Before initiating infliximab therapy, patients should be tested for latent tuberculosis (TB) infection using either the Mantoux tuberculin skin test (TST) or an interferon-gamma release assay (IGRA). This is because TNF-alpha is essential for maintaining the latency of Mycobacterium tuberculosis, and suppression of TNF-alpha with infliximab can reactivate latent TB. Reactivation of TB can be severe and even life-threatening. IGRA tests, such as the QuantiFERON-TB Gold test, are preferred over TST in patients with a history of BCG vaccination or in those with a recent history of TB exposure.

**Why Each Wrong Option is Incorrect**
**Option A:** Hepatitis B serology - While important for patients on immunosuppressive therapy, hepatitis B serology is not directly related to the initiation of infliximab therapy.

**Option B:** Complete Blood Count (CBC) - Although a CBC may be performed as part of a routine pre-treatment evaluation, it is not a specific test required for patients starting infliximab.

**Option C:** Renal function tests - These may be important for patients with pre-existing renal impairment, but are not a specific test required for the initiation of infliximab therapy.

**Clinical Pearl / High-Yield Fact**
Infliximab and other biologic agents can also increase the risk of reactivating hepatitis B virus (HBV) in patients with chronic HBV infection, making hepatitis B serology an essential evaluation before starting treatment.

**Correct Answer:** C. TB screening using either Mantoux TST or IGRA.