Gamma interferon assay Misuse?

Gamma interferon measurement should be use cautiously in INDIA.


Gamma interferon produced by lymphocytes against tubercular antigens is measured and utilized to test the patient’s immune reactivity against tubercular bacteria. It means the results of this test are depends upon the concentration of gamma interferon produced by lymphocytes. These tests are available by the name of TB FERON TEST, QUANTIFERON TB (TB GOLD) test. I want to highlight some point about this test.

1. This test detects infection of tubercular bacteria. This actually means that body of patient is infected with TB bacillus. However the disease may be latent or active. This means the test actually cannot differentiate active or inactive tuberculosis. In India I have seen that many doctors are relying on this test for diagnosis of active disease which leads to wrong treatment.

2. The other test for detection of Infection of tuberculosis is Tuberculin skin test or Mantaux test. Mantaux test is very cheap in comparison to measurement of gamma interferon and provides similar information.

3. With both of the above test additional test are needed for exclusion of active TB or confirm latent TB.

4. India is a country where the infection rate is very high and latent TB is usually not treated because of fear of development of resistant against Isoniazed (Drug for latent TB).So in most of the cases these results should be positive. If this test result comes negative one should think of immune- compromised status of patient.

5. To conclude I suggest interferon gamma measurement is diagnostic of TB infection not TB disease (Active tuberculosis). Mantaux test can provide similar information in most of the cases and quite cheap. Interferon gamma measurement should be reserve for special situation or where Mantaux test are contra indicted for Eg. Severe dermatitis. Comparison of two test ............

Tuberculin skin test                                             Gamma interferon

Cheap                                                                                Costly

available anywhere                                                        require good lab (ELISA)

Reader skills required but can be learn easily                  Lab training required

Reader bias may be present                                           Reader bias not present

May be positive in BCG vaccinated                               Not affected with BCG Vaccination

May be positive in infection with NTM                          Not affected by NTM

Booster phenomenon may be                                        No booster phenomenon

Two visit needed                                                                      Single visit