Question

After doing a chest x-ray, your doctor says the results are inconclusive. So, you are put on a six-month course of isoniazid to be safe. About six months later, while sitting in your medical microbiology class during a lecture on tuberculosis, you suddenly realize why you had that positive reaction to the skin test six months earlier. It had nothing to do with being infected, but was because you were born in Norway and your family moved to the United States when you were four years old.

3. What is going on here? Discuss in detail. 4. A while later, you told a friend of yours who is HIV-positive about your TB scare. She said that her doctor doesn't typically use the TB skin test on her, even though people with HIV are more susceptible to TB. Why is the skin test not always a reliable TB test for those with HIV?

Answer 1

Tuberculin skin test also called Mantoux test is used to diagnose the latent TB, it does not tell about the active TB infection.

So in this there is positive Mantoux test and inconclusive XRay due to:-

1. There might be a latent infection that means the there is inactive TB bacteria in body. These scanning be passed to others.

2.When migrating from Norway to USA he must have been Vaccinated with BCG vaccine. Due to previous vaccinaton of BCG there is positive Montoux test.

Tuberculin skin test is not done in Patients with HIV because:-

1. As already the patiests are immunocompromised so due to decreased immunity the tests shows false negative values.

Sensitivity is lost of this test during HIV patient.

So in HIV infected patients, the cutoff value of the tuberculin skin test is often reduced from an induration of 10 mm in diameter to one of 5 mm in diameter to compensate for loss of sensitivity.