Why does my ppd itch

A measured amount of PPD in a shot is put under the top layer of skin on your forearm. This is a good test for finding a TB infection. It is often used when symptoms, screening, or testing, such as a chest X-ray , show that a person may have TB.

A tuberculin skin test cannot tell how long you have been infected with TB. It also cannot tell if the infection is latent inactive or if you have active TB that can be passed to others. For a tuberculin skin test, you sit down and turn the inner side of your forearm up. The skin where the test is done is cleaned and allowed to dry. A small shot of the tuberculosis antigen purified protein derivative, or PPD is put under the top layer of skin.

The fluid makes a little bump wheal under the skin. A circle may be drawn around the test area with a pen. There is a very slight risk of having a severe reaction to the tuberculin skin test, especially if you've had tuberculosis TB.

An allergic reaction can cause a lot of swelling and pain at the site. You may have a sore. You cannot get a TB infection from the tuberculin skin test. That's because no live bacteria are used for the test. Redness alone at the skin test site usually means you haven't been infected with TB bacteria. A firm red bump may mean you have been infected with TB bacteria at some time. The size of the firm bump not the red area is measured 2 to 3 days after the test to find out the result.

A positive reaction usually remains visible for about 1 week. Taking medicines that suppress the immune system, such as corticosteroids. Conditions that weaken the immune system, such as HIV infection or cancer. The result also may be affected if a person is severely malnourished.

Some vaccinations for infections, such as measles, mumps, rubella, polio, or chickenpox, given within 6 weeks before the tuberculin test. A recent infection with one of these viruses can also interfere with test results for a short period of time. The skin test also may be positive if the person has an infection caused by a mycobacterium other than the one that causes TB. A very recent TB infection. It takes 2 to 10 weeks for the immune system to react to TB bacteria.

Age younger than 3 months old. The booster effect is a weak or no reaction to one TB skin test followed by a strong reaction from a second test. But the strong reaction to the second test does not mean that the person has just become infected with TB.

Instead, the reaction may be because of: A TB infection that occurred long ago. So the first TB skin test stimulates boosts the immune system, which then reacts strongly to the second skin test. Infection with bacteria similar to Mycobacterium tuberculosis. This may also cause a first TB skin test to boost the immune system, allowing it to react strongly to a second test, even though a new TB infection has not occurred. Other tests, such as a chest X-ray, sputum cytology, and sputum culture, may be done to confirm an active TB infection when a skin test is positive.

A person who has a positive skin test or chest X-ray, but no TB symptoms, is usually thought to have a TB infection that cannot be passed to others latent TB. Chest X-Ray Sputum Cytology Sputum Culture Among hospital workers or others who have periodic skin tests, a second test done within a few weeks of a negative test may be positive, even though the person was not infected between the two tests. These results called the booster effect may indicate a TB infection that occurred a long time ago or a previous BCG vaccination.

No more tests are needed for a person with a negative tuberculin skin test who has no symptoms of active infection and no history of being exposed to TB. Some people do not react to a tuberculin skin test even if they have tuberculosis. In these cases, other skin tests may be done. If there is a skin reaction, then the tuberculin skin test is probably correct.

Rapid blood tests to diagnose TB have been approved by the U. Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:. Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

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