Mycobacterium tuberculosis

Question 1

Describe the Tuberculin skin test (TST) to test for TB.

Answer 1

Small amount of tuberculin is injected into the skin. Patient returns 48-72 hours later to have reaction read where they measure induration (firm swelling) not redness.

Question 2

What result would be indicative of a positive TST test?

Answer 2

Induration >15mm for people with no known risk factors.

Question 3

Describe the Interferon gamma release assay.

Answer 3

Special collection vials coated with non-infectious TB antigens. Interferon gamma is released in TB patients and can be detected through ELISA.

Question 4

What are the advantages of the Interferon gamma release assay over the TST?

Answer 4

Only 1 blood test needed, not subject to bias, and not affected by vaccination.