A 32-year-old man with Crohn's disease (Montreal classification: ileocolonic, inflammatory, without perianal disease) is on azathioprine with partial response. He is considered for biologic therapy. Anti-TNF therapy with infliximab is planned. Prior to initiating infliximab, which screening is most critical?
- A TPMT genotyping to assess azathioprine metabolite levels
- B Serum infliximab trough level before first infusion
- C Screening for latent tuberculosis (IGRA or tuberculin test) and HBV serology ✓
- D Colonoscopy with biopsies to exclude dysplasia prior to anti-TNF therapy
Explanation
Before initiating anti-TNF therapy, the critical safety screens are: (1) latent TB screening — infliximab can reactivate latent TB, which is potentially fatal; IGRA (preferred) or TST should be performed and prophylactic isoniazid started for 4–8 weeks before infliximab if IGRA positive; (2) HBV surface antigen and core antibody — anti-TNF can cause HBV reactivation, requiring prophylactic antivirals (entecavir/tenofovir) in HBsAg+ or HBcAb+ patients. TPMT genotyping is relevant for azathioprine dosing (before starting thiopurine), not anti-TNF. Trough levels are used for monitoring during therapy, not pre-screening.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.