Internal Medicine Grand Rounds

March 14, 2019
Pulmonary TB: Hobby, Hoofbeats, and Paradox
Douglas Hornick, MD

LTBI Testing upgrade:

Skin test – contains multiple antigens. Cross reacts with BCG

QuantiFERON family: Positive IGRA test is not positive because of prior BCG vaccine. That’s one of the values of the test.

IGRA – done in test tube while TST is done in vivo

No boosting phenomenon with IGRA test, only one test is needed. TST requires patient to return for reading.

IGRA has one standard and no inter-reader variability. Different thresholds for TST while there is only one standard fro IGRA.

When Can IGRA replace TST

  • Contact investigation

  • bcg vaccination history

  • low risk person

  • screening homeless and other unreliable people

Latent TB Infection Dx and treatment


Chest x-ray to rule out evidence for active TB

Treatment options

  • INH 300 mg daily x 6-9 months OR

  • Rifampin 600 mg daily x 4 months OR

  • INH and Rifapentine 900 mg Qwk x 12 doses (most expensive option but often covered by public health officials)

    • Public health officials will monitor treatment and make sure it is complete. They will get the medication covered in Iowa. They are very helpful in the state of Iowa.

Active TB diagnosis and Treatment

  • Tests required for diagnosis:

    • typical chest x-ray

      • heterogeneous (fibronodular infiltrate

      • Upper lobe

      • apical pleural thickening

      • volume loss (Hildur retraction upward, trachea shifted towards, diaphragm tenting

    • AFB stain and culture from sputum

      • culture-based drug susceptibility phenotype remains “gold” standard

    • Molecular (genotypes) methods emergent

      • UIHC Xpert MTB/RIF

        • PCR test. Identifies TB and amplifies rpoB gene within 1 day.

        • Sensitivity and specificity over 95%

        • Closed system, no biohazard.

CDC: molecular detection of drug resistance.

Whole genome sequencing *WBS) w/in 203 days

Improving resistance predictions for 1st, 2nd, line and new drugs

daveats: discordance with phenotypic data, clinical outcomes

Negative IGRA doesn’t rule out active TB. Start treatment for those you suspect have drug resistance.

Diagnose with sputum AFB, sputum NAAT, IGRA

culture more sensitive than NAAT. NAAT is aimed at specificity.

Need 10,000 bacteria per cc for positive smear. culture can go all the way down to 50 per cc, much more sensitive. Even BAL is not that sensitive for smears.

CT chest is not needed when upper lobe, caviars consolidation. May help define lymphadenopathy, pleural or pericardial effusion, or military pattern. May reveal alternative dx. If suspect TB, obtain sputum smear, if positive you do not need CT.

4 drugs x 26 weeks given by directly observed therapy.

8 weeks intensive phase (INH, RIF, PZA, EMB

18 weeks INH, RIF


90% of patients even in the areas where totally resistant strains are the most prevalent, are sensitive to first line drugs.

HIV, anti-TNF, malnutrition, Vit D deficiency, viral infection put patients at risk to progress from latent TB to active TB. Will often be asymptomatic when in sub-clinical phase. May be picked up from screening.

Noon Conference Lecture

Dr. Hornick

March 2017