A 50-year-old patient on high-dose immunosuppression for a renal transplant has a negative TST (Mantoux) of 5 mm. An IGRA (QuantiFERON-TB Gold) is also negative. Which statement best explains the limitation of these tests in this patient?
- A IGRA is falsely negative due to BCG vaccination
- B Both tests have reduced sensitivity in anergy due to immunosuppression ✓
- C TST is falsely negative due to prior BCG vaccination
- D IGRA is falsely negative due to cross-reactivity with NTM
Correct answer: B. Both tests have reduced sensitivity in anergy due to immunosuppression
Explanation
Both TST and IGRA depend on a functional T-cell response. In immunosuppressed patients, anergy causes false-negative results in both tests. BCG affects TST specificity, not IGRA. NTM cross-reactivity is minimal for IGRA due to ESAT-6/CFP-10 antigens.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.