Multi-drug-resistant tuberculosis screening
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]
Overview
Screening for tuberculosis is generally done with using a mantoux tuberculin skin test, also known as a tuberculin skin test or a PPD. The test involves injecting a small amount of a purified protein derivative of the tuberculosis bacterium intradermally, and watching for a reaction in the following days.
Screening
Mantoux Tuberculin 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. 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.
The skin test reaction should be read between 48 and 72 hours after administration. A patient who does not return within 72 hours will need to be rescheduled for another skin test.
The reaction should be measured in millimeters of the induration (palpable, raised, hardened area or swelling). The reader should not measure erythema (redness). The diameter of the indurated area should be measured across the forearm (perpendicular to the long axis).
TST is contraindicated only for persons who have had a severe reaction (e.g., necrosis, blistering, anaphylactic shock, or ulcerations) to a previous TST. It is not contraindicated for any other persons, including infants, children, pregnant women, persons who are HIV-infected, or persons who have been vaccinated with BCG.
In some persons who are infected with M. tuberculosis, the ability to react to tuberculin may wane over time. When given a TST years after infection, these persons may have a false-negative reaction. However, the TST may stimulate the immune system, causing a positive, or boosted reaction to subsequent tests. Giving a second TST after an initial negative TST reaction is called two-step testing.
Two-step testing is useful for the initial skin testing of adults who are going to be retested periodically, such as health care workers or nursing home residents. This two-step approach can reduce the likelihood that a boosted reaction to a subsequent TST will be misinterpreted as a recent infection.
Classification of Tuberculin Reaction
Skin test interpretation depends on two factors:
- Measurement in millimeters of the induration.
- Person’s risk of being infected with TB and of progression to disease if infected.
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| Tuberculin Reaction | Considered a Positive Result in: |
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| ≥ 5 mm |
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| ≥ 10 mm |
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| ≥ 15 mm |
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| Table adapted from CDC[1] | |
| False-Positive Reactions | False-Negative Reactions |
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Some persons may react to the TST even though they are not infected with M. tuberculosis. The causes of these false-positive reactions may include, but are not limited to, the following:
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Some persons may not react to the TST even though they are infected with M. tuberculosis. The reasons for these false-negative reactions may include, but are not limited to, the following:
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| Table adapted from CDC[1] | |
Recommendations for Human Immunodeficiency Virus (HIV) Screening in Tuberculosis Clinics Adapted from CDC[2]
- CDC recommends HIV screening for all TB patients after the patient is notified that testing will be performed, unless the patient declines (i.e., opt-out screening). This includes persons with TB disease and persons with latent TB infection.
- Routine HIV testing is also recommended for persons suspected of having TB disease, persons diagnosed with latent TB infection, and contacts to TB patients.
- Prevention counseling and separate written consent for HIV testing should no longer be required.
- These recommendations are aimed at eliminating missed opportunities for HIV screening and reducing significant barriers to HIV testing in health care settings by:
- Opt-out screening is defined as performing HIV testing after notifying the patient that the test will be performed, and although the patient may decline or defer testing, it is strongly recommended. Assent is inferred unless the patient declines testing.