Chest Conference4 2009
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  • 1. Chest Conference TB Update Case Presentation Ramin Khashayar, MD April 7, 2009
  • 2. Presentation of the Case
    • 63 y.o. woman with a long standing diagnosis of U.C. treated with moderate to large doses of oral corticosteroid
    • Pt developed increasing cough and had a CXR and chest CT scan done as part of the work up
    • CXR revealed a new RUL infiltrate
  • 3. Presentation of the Case
    • Chest CT confirmed the presence of RUL infiltrate without associated LAD or pleural effusions
    • She reported 2 week h/o of low grade fevers and mild night sweats but no wt loss
    • There was no hemptysis
  • 4. Presentation of the Case
    • Laboratory testing was otherwise negative
    • TST was negative (no controls done)
    • Patient lives in W.C but had an extensive travel history in Asia and Africa
    • She denies know TB exposure and had not traveled in fungal endemic areas
  • 5. Presentation of the Case
    • She was seen in the office 3 days ahead of a planned air travel to Hawaii
  • 6. TB overview
    • Approxiamtely 1/3 of the work population had LTBI
    • An estiamted 10 million people worlwide have active TB
    • 2 million people a year die of tuberculosis
  • 7. TB overview
    • In the US, foreign-born persons from high TB risk areas have a 10-fold increased risk of developing TB
    • The risk of TB is highest in first five years after arrival but continues to be higher throughout their lives
    • The risk of TB in immigrant who travel back to the country of origin is higher than their cohort who don’t travel back
  • 8. TB overview
    • CDC recommend targeted screening for immigrants from high risk countries especially during the first five years after arrival
    • Local Health department recommend the use if IGRA (QuantiFERON-TB Gold assay) as this is more specific in people vaccinated with BCG
  • 9. QuantiFERON-TB Gold assay
    • One of three IGRAs, and one approved by FDA and available at JM (sent out to Sacto county lab)
    • It required heparinized fresh whole blood that needs to be tested within 12 hour as it requires viable lymphocytes
  • 10. QuantiFERON-TB Gold assay
    • Whole blood aliquots are mixed with two MTB (ESAT-6 and CFP-10) antigens, negative control mixture (saline) and a positive control mixture (mitogen) for 16-24 h
    • If the lymphocytes react to MTB antigen, they release gamma interferon that can be measures and compared to the negative and positive control samples and resultes as positive, nagative or indeterminate
  • 11. QuantiFERON-TB Gold assay
    • The major advantage of the test is lack of cross reactivity with BCG, or non-tuberculosis mycobacteria
    • It is also a one step test that does not require a second visit
    • It requires an expert lab as it is a biological test and can be subject to variability
  • 12. QuantiFERON-TB Gold assay
    • It requires fresh heparinized blood
    • It’s performance in children and immuno-compromized host (HIV/ steroids) is not known
    • Hard to study as TST itself is a poorly sensitive and non-specific test
  • 13. QuantiFERON-TB Gold assay
    • In one study, comparing two types of IGRA with TST, TST was found to be less sensitive than IGRA in HIV, liver transplant and hematologic malignancy patients (15-18% vs 10% positive rates)*
    • * Richeldi et al, Chest, April 2, 2009
  • 14. QuantiFERON-TB Gold assay
    • A study of 44 suspected pulmonary and 21 extrapulmonary TB pts, found QFT-G to be 75% and 76% sensitive vs 68% and 62% for TST*
    • *Ak et al, Jon. J. Infec. Dis., 2009
  • 15. QuantiFERON-TB Gold assay
    • In one study, 90 pts underwent bronchoscopic evaluation for TB
    • 28 had proven TB, 52 did not
    • In TB pts QFT-G was positive in 79%, TST in 57%
    • *Kobashi et al, Internal Medicine, 2007
  • 16. QuantiFERON-TB Gold assay
    • Locally, we quote a 20% false negative rate.
    • The sensitivity is probably higher that TST, and it is not complicated by BCG vaccination
    • The false negative pts with QFT-g and TST do not overlap
    • One study suggested that if both tests are negative, TB is even less likely (?)
  • 17. TB Review, PT classification
    • TB1: No evidence of TB or LTBI
    • TB2: LTBI
    • TB3: Active TB
    • TB4: Old TB (CXR w/o change for 3 mo, no clinical or microbiologic suspicion for TB
    • TB5: TB suspect, high prob or low prob
  • 18. TB