HY lecture info:
TB diagnosis2
PPD skin test is performed first diagnostically. If history of BCG vaccine, do interferon-gamma release assay (IGRA) instead. Do not do IGRA in addition to PPD.
If PPD is negative, repeat after one week. If negative again, no further studies indicated. Repeats performed within 1 week may cause a false (+) secondary to a “booster reaction.”2
If IGRA is negative, no further studies indicated.
If PPD or IGRA is positive, do CXR. Do not repeat positive PPD tests.
If CXR is negative, treat for latent TB / give TB prophylaxis. On the USMLE, “treatment for latent TB” and “administer TB prophylaxis” mean the same thing.
If CXR is positive, treat for active TB.
Positive PPD test3
Measure induration only. Erythema does not count.4
5+ mm
- Recent contact with people with active TB
- HIV + status
- Organ transplant recipients
- Chronic prednisone use (>15mg/day for >1 month); anti-TNF-α agent use
- Findings consistent with TB on CXR
10+ mm
- Immigrant status (Western countries not included)
- IV drug users
- Healthcare workers; prison workers; homeless shelter personnel
- TB laboratory personnel
- Children under 4 years of age
15+ mm
- Everyone
Tx of latent TB5
- 9 months INH + pyridoxine (vitamin B6) – The USMLE Steps 1 and 2CK assess this as the answer.
- 4 months rifampin
- 3 months INH + rifapentine + pyridoxine
- Vitamin B6 must be given with INH to prevent vitamin B6 deficiency.6
Tx of active TB7
- Rifampin, INH, pyrazinamide, ethambutol (RIPE) for 2 months, followed by RI alone for 4 more months (6 months total)
- And of course add pyridoxine (annoying that it sounds similar to pyrazinamide)
2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3481914/
3) https://www.cdc.gov/tb/topic/treatment/decideltbi.htm
4) https://www.cdc.gov/tb/publications/posters/images/Mantoux_wallchart.pdf
5) https://www.cdc.gov/tb/topic/treatment/ltbi.htm
