TB Flashcards
Control of TB replication is dependent on what factors?
TNF alpha, IFN gamma, T cell
How does a mantoux test work?
Intradermal injection of purified protein derivative, if previously exposed will show a delayed-type hypersensitivity reaction
What compromises the specificity of the mantoux test?
Previous BCG exposure
Previous exposure to non-tuberculosis mycobacteria
Inter operator variability
How does the quantiferon gold test work?
If infected with TB, the circulating T lymphocytes will produce IFN gamma when re-exposed and this is measured
What is the advantage of quantiferon gold over mantoux?
Not affected by previous B G or other mycobacterium exposure
What are the 4 tubes in a quantiferon gold test?
Positive control (tests ability to produce interferon gamma)
Negative control (adjusts for background level of interferon gamma)
CD4 T cell response
CD4 and CD8 T cell response
What does an indeterminate quantiferon gold test mean?
In the positive control test there is inadequate interferon gamma production
What are the disadvantages of the quantiferon gold test?
May be negative in active disease and level does not predict active vs latent TB
What is the sensitivity and specificity of nucleic acid amplification tests for TB detection of sputum samples?
Sensitivity 85% specificity 98%
How long does it take to culture TB?
6-8 weeks
What are the CSF findings for TB meningitis?
High WCC (lymphocytic), high protein, low glucose
What is the most important risk factor for progression to active TB?
HIV
What is the treatment for latent TB?
9 months of isoniazid
Can also use 4 months of rifampicin
What is the side effect of isoniazid?
Severe hepatotoxicity, rash, peripheral neuropathy
What percentage of the worlds TB is resistant to isoniazid?
15%
