Cvs Mantoux Test (2024)

FAQs

What should be the result of Mantoux test? ›

The reference range of the induration is 0-15 millimetres at an increment of 5 mm, 10 mm and 15 mm. An induration size of more than 15 mm is considered positive in a normal patient. A swelling of less than 4 mm is considered negative. Why do I need the Mantoux test?

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.

Within 48 to 72 hours, a positive TB skin test is marked by an area of reddish induration greater than 10 mm. It is the induration (firm bump) that is gently palpated that determines the size, not the area of redness. This reaction is slightly larger than the average positive test 17 mm in size.

Due to the test's low specificity, most positive reactions in low-risk individuals are false positives. A false positive result may be caused by nontuberculous mycobacteria or previous administration of BCG vaccine. Vaccination with BCG may result in a false-positive result for many years after vaccination.

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.

The skin test reaction should be read between 48 and 72 hours after administration by a health care worker trained to read TST results. A patient who does not return within 72 hours will need to be rescheduled for another skin test.

A reasonable approach is to aim for reading the TST sometime in the morning if placed in the morning or sometime in the afternoon if placed in the afternoon (about 44-47 hours after placement). Reading late: Reading a positive TST late is no problem! Per CDC, a positive test may be read up to 7 days after placement.

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.

After the test, you should avoid using bandages, putting on lotion, or scratching the test area because it may affect the results. You can wash the area with water, but do not wipe or scrub. If the area itches, put an ice cube or cold cloth on it.

Can you have a false positive Mantoux test? ›

Some persons may have a positive result from a TB skin test even though they are not infected with TB bacteria. The causes of these false-positive results may include, but are not limited to, the following: Previous TB vaccination with the bacille Calmette Guérin (BCG) vaccine.

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.

What if my TB skin test is negative? 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.

In a healthy person whose immune system is normal, induration greater than or equal to 15 mm is considered a positive skin test. If blisters are present (vesiculation), the test is also considered positive. In some groups of people, the test is considered positive if induration less than 15 mm is present.

Like the Mantoux, the Heaf test is read at 48–72 hours and the reaction is scored as five grades: grade 0 is no reaction; grade I is at least four discrete papules; grade II is confluent papules forming a ring; grade III is a disc of induration <10 mm; and grade IV is a disc of induration >10 mm or vesicular formation.