If you are a health care worker, work in schools, nursing homes, or any profession that involves contact with people, your employer might require you to get a TB screening. In this article, we will review the various options including TB skin test called Mantoux test. 

What options are available to screen a person for Tuberculosis?

1. Tuberculin skin test
2. Qauntiferon test which is a three tube blood test

What is Mantoux TB skin test?

The Mantoux tuberculin skin test (TST) is the standard method of determining whether a person is infected with Mycobacterium tuberculosis. Reliable administration and reading of the TST requires standardization of procedures, training, supervision, and practice.

How is the TST Administered?

The TST is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) into the inner surface of the forearm. The injection should be made with a tuberculin syringe, with the needle bevel facing upward. The TST is an intradermal injection. When placed correctly, the injection should produce a pale elevation of the skin (a wheal) 6 to 10 mm in diameter.

How is the TST Read?

The skin test reaction should be read between 48 and 72 hours after administration.

What should we do if a patient fails to follow up?

A patient who does not return within 72 hours will need to be rescheduled for another skin test.

How do you measure the reaction?

The reaction should be measured in millimeters of the induration (palpable, raised, hardened area or swelling).

For most people, an induration of 15 mm or more is considered positive.

Should the redness of the reaction be included in the measurement?

The reader should not measure erythema (redness).

How do you measure?

The diameter of the indurated area should be measured across the forearm (perpendicular to the long axis).

How Are TST Reactions Interpreted?

An induration of 5 or more millimeters is considered positive in

» HIV-infected persons

» A recent contact of a person with TB disease

» Persons with fibrotic changes on chest radiograph consistent with prior TB

» Patients with organ transplants

» Persons who are immunosuppressed for other reasons (e.g., taking the equivalent of >15 mg/day of prednisone for 1 month or longer, taking TNF-α antagonists)

An induration of 10 or more millimeters is considered positive in

» Recent immigrants (< 5 years) from high-prevalence countries

» Injection drug users

» Residents and employees of high-risk congregate settings

» Mycobacteriology laboratory personnel

» Persons with clinical conditions that place them at high risk

» Children < 4 years of age

» Infants, children, and adolescents exposed to adults in high-risk categories

An induration of 15 or more millimeters is considered positive in

any person, including persons with no known risk factors for TB.

However, targeted skin testing programs should only be conducted among high-risk groups.

What is the alternative to TB skin test?

QuantiFERON-TB Gold (QFT) is a three tube blood test that aids in the detection of Mycobacterium tuberculosis, the bacteria which causes tuberculosis (TB).

QFT is highly specific and sensitive: a positive result is strongly predictive of true infection with M. tuberculosis.

Can QauntiFeron-TB Gold test determine if I have active infection?

No. Like the TST and other IGRAs, QFT cannot distinguish between active tuberculosis disease and latent tuberculosis infection, and is intended for use with risk assessment, radiography, and other medical and diagnostic evaluations.

Like any diagnostic aid, QFT cannot replace clinical judgment.

W8MD locations where a TB skin test is offered