Tuberculin: skin test in screening for tuberculosis (TB)

By Cristiano Antonino On Dec 20, 2022

The tuberculin skin test is considered the primary means of screening for tuberculosis (TB) infection

Tuberculin is a protein fraction of the tubercle bacillus that provokes a delayed immune response in the body.

When the tuberculin test is performed

The tuberculin test is performed whenever one wants to know whether there has been previous contact with the Mycobacterium Tuberculosis, responsible for tuberculosis: a positive reaction indicates that the test subject has had previous contact with the tuberculosis bacterium, which is not always the same as being ill.

It is usually considered appropriate as an initial screening test in asymptomatic individuals and is recommended for

those who have spent time with a person with TB in the infectious phase
those who live in places and countries where TB is widespread
intravenous drug users, the immunocompromised and those infected with HIV.

As part of special prevention programmes, the test is also performed on primary and secondary school pupils and hospital staff.

How the tuberculin test is performed

After the skin has been thoroughly disinfected, 1/10 ml of tuberculin is injected into the dermis of the volar surface of the forearm using an insulin syringe and a very fine needle.

The injection, which is not painful, causes a pomphoid sensation on the skin that should not be rubbed or covered with a plaster to avoid possible skin allergies that would alter the test, and which slowly reabsorbs (intradermal Mantoux).

In addition, the inoculation area should not be washed or scratched

In addition to the Mantoux intradermoreaction, a pre-packaged test called the ‘tine test’ can also be used, which consists of a plastic disc with four tuberculin-soaked tips that is applied like a stamp in the same arm area as the Mantoux intradermoreaction.

The test result awaits the skin response, which manifests itself 48/72 hours after inoculation and, in the case of a positive result, causes an area of hardened skin, papule, surrounded by erythema of varying size.

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