Tuberculosis: Screening

Question 1

What is the main technique used to screen for latent TB?

Answer 1

The Mantoux test.

Question 2

In recent years, what other test has been used to detect latent TB?

When might it be used?

Answer 2

Interferon-Gamma Blood Test

• The Mantoux test is positive or equivocal
• People where a tuberculin test may be falsely negative

Question 3

Tell me about how the Mantoux test is injected, how much, when & how to interpret it?

Answer 3

• 0.1 ml of 1:1,000 purified protein derivative (PPD) injected intradermally
• result read 2-3 days later
• < 5mm - negative. If unvaccinated can be given BCG.
• 5-15mm - Should not be given BCG - may be due to TB infection or BCG. Consider Interferon Gamma Release Assay.
• >15mm - strongly positive - suggests TB infection.

Question 4

What can cause the Mantoux test to be falsely negative?

Answer 4

• Miliary TB
• Sarcoidosis
• HIV
• Lymphoma
• Very young age (e.g. < 6 months)

Question 5

What test is no longer used?

Answer 5

The Heaf test