I've tutored dozens of med students through board prep, and TB questions are free points — if you avoid these common traps.

1. Primary TB is in the LOWER lobes, reactivation is in the UPPER lobes.

Students constantly mix these up. Primary = where air goes first (middle/lower lobes). Reactivation = where O₂ is highest (apices). The obligate aerobe loves oxygen.

2. Read TST induration, not erythema.

The redness around the injection site means nothing. You're measuring the firm, raised area (induration) at 48-72 hours. And yes, the cutoff changes based on risk factors.

3. IGRA > TST in BCG-vaccinated patients.

BCG causes false-positive TST results. IGRA uses Mtb-specific antigens (ESAT-6, CFP-10) that aren't in the BCG strain, so it won't cross-react.

4. INH causes peripheral neuropathy. The answer is always B6.

INH depletes pyridoxine (vitamin B6). Give B6 prophylactically. In INH overdose, the treatment is also IV B6.

5. MDR-TB = resistant to INH AND Rifampin.

Not just one. Both. If GeneXpert shows rifampin resistance, treat as MDR until proven otherwise.

I built a full course that breaks all of this down — pathophys, diagnosis, pharmacology, special populations, and a final quiz.