Cvs Mantoux Test (2024)

FAQs

What if TB skin test is less than 10 mm? ›

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 by a health care worker trained to read TST results.

It is a test for diagnosis of LTBI, and is not recommended for the diagnosis of active disease – sensitivity is only 70–85%. More importantly the TST cannot distinguish active disease from latent infection. Hence the specificity for active TB is low.

The Mantoux test result is based on the reaction of the injection on the skin. The reaction should be checked by a doctor or medical professional within 48 to 72 hours of injection. The lump formed on the skin has to be measured on a scale of millimetres without considering the surrounding redness of the skin.

Induration of ≥15 mm is considered positive in

All U.S. health care employees should have baseline TB screening, including an individual risk assessment which is necessary for interpreting any test result.

Ten mm or more is positive in

Residents and employees of high-risk congregate settings (e.g., prisons, nursing homes, hospitals, homeless shelters, etc.)

The results of this test must be interpreted carefully. The person's medical risk factors determine at which increment (5 mm, 10 mm, or 15 mm) of induration the result is considered positive. A positive result indicates TB exposure. 5 mm or more is positive in. An HIV-positive person.

In some individuals, the reaction to tuberculin antigen wanes over time, which results in a false-negative reaction. In individuals with a prior TB infection from years earlier, sensitization to tuberculin may be weak, and there may be a false-negative PPD test.

Skin test. A tiny amount of a substance called tuberculin is injected just below the skin on the inside of one forearm. Within 48 to 72 hours, a health care worker will check your arm for swelling at the injection site. The size of the raised skin is used to determine a positive or negative test.

The test is “negative” if there is no bump (or only a very small bump) at the spot where the fluid was injected. A negative TB skin test usually means that you don't have TB. In some situations, you may need to have another TB skin test later.

After 2 or 3 days, you must return to have a health care worker read your skin test. You may have swelling or a bump where the testing fluid was injected. The health care worker will measure the bump or swelling and will tell you if your skin test reaction is positive or negative.

Can Mantoux test be false positive? ›

However, even use of the preferred skin test technique (intradermal injection of purified protein derivative via the Mantoux method) can lead to either false positive or false negative results.

The skin test reaction should be read between 48 and 72 hours after administration. If the test is not read within 72 hours, another TST should be placed unless the amount of induration is ≥ 10 mm within 7 days after placement.

A positive Mantoux test means you may have a TB infection. your doctor may recommend another blood test or a chest X-ray to determine the type of TB infection. There may also be a sputum test to look for infections.

It does not mean you have an active TB infection. The test may be seen as positive if the skin where you were injected is hard, raised, red, and swollen. But redness alone is not considered a positive test result. In many cases, a healthy immune system will surround the TB bacteria soon after you are infected.

Possible causes of false-negative reactions include: anergy, recent TB infection (within 8-10 weeks), old TB infection, young age (<6 months), recent live-vaccine, overwhelming TB disease, viral illnesses, incorrect administration or interpretation of TST.

Patients in hospitals or nursing homes, children under 4 years of age, and patients who use injection drugs with ≥10 mm induration should be considered positive. Anyone 4 years and older with a low risk for TB infection is considered positive with ≥15 mm induration.

An induration of less than 5 millimeters (mm) is a negative result. If you have symptoms or know you've been exposed to someone with TB, a doctor may recommend you get another test. If the induration is at least 5 mm, it is considered positive in people who: have had recent contact with a person with TB.

A TST measuring 10 mm or greater is considered positive in the remainder of the population at high risk of developing tuberculosis. For patients at low risk for the development of tuberculosis the TST is considered positive at 15 mm of induration or greater.

TST results between 5 and 9 mm of induration are negative for most health care workers but are positive for those with certain risk factors.