PPD Skin Test for Tuberculosis (TB)

A PPD test is a skin test for TB infection that uses tuberculin purified protein derivative, which is what PPD stands for. It is the same test as the Mantoux test and the tuberculin skin test. It shows whether the immune system has met TB germs³. It cannot tell inactive TB from active TB disease on its own³. The reaction is a delayed immune response by T cells to proteins that TB bacteria release as they grow (Yang, 2012). The test is named after Charles Mantoux (1877-1947). The purified protein derivative itself was developed in 1934 by the biochemist Florence Seibert.

How the reaction is measured decides the result. The guide on how to read a tuberculosis (TB) skin test walks through the measuring.

No: the PPD test is not a vaccine, even though many people call it a TB shot. It tests for infection and gives no protection against TB. The TB vaccine is BCG, which is not widely used in the US. The FDA shortage list, current as of Sept. 28, 2026, shows BCG vaccine for TB prevention as currently unavailable. The page on the BCG vaccine for tuberculosis explains why it is rare here.

The PPD test contains 0.1 mL of tuberculin, a purified protein made from TB bacteria. Two tuberculin products are approved in the US, Tubersol and Aplisol. In repeat testing, switching between the two products can make a result appear to change⁶. So can switching between a skin test and a blood test⁶. Each 0.1 mL dose holds 5 tuberculin units, with small amounts of polysorbate 80 and phenol in a buffered salt solution⁵. The page on Tubersol and Aplisol compares the two products.

The PPD test is placed by injecting 0.1 mL of tuberculin just under the skin of the inner forearm. Done correctly, it raises a pale bump 6 to 10 mm across. Placement follows five steps¹.

1. Clean the skin with a germicide and let it dry, away from red or swollen skin.
2. Use a 27-gauge tuberculin syringe, bevel up.
3. Watch for the pale bump, which forms at once.
4. If the dose goes in wrong, place a new test at least 2 inches from the first.
5. Know that an injection below the skin instead of into it cannot be read.

The page on tuberculosis skin test placement covers each step in detail.

The PPD test is read 48 to 72 hours after it is placed. A trained health worker measures the firm swelling in millimeters and ignores redness. If you cannot come back within 72 hours, the test has to be placed again². The Minnesota health department tells providers that patients and health care workers must not record their own results⁹. A skin test red but no bump reads as negative for that reason.

A PPD test takes two visits: the injection, then a reading 48 to 72 hours later. A two-step test doubles that, with the second test placed 1 to 3 weeks after the first is read. The Hawaii health department counts at least 2 calendar days for a single skin test. A two-step test takes at least 9. A TB blood test needs only one visit⁴.

A PPD result is the width of firm swelling in millimeters, and the cutoff for positive depends on your risk. Redness alone is not counted, and a reaction below your cutoff is negative. The reader measures the swelling across the forearm, at a right angle to its length¹.

The page on tuberculosis (TB) test results covers blood test and X-ray results too.

Failing a PPD test means it was positive, which shows TB germs in the body but not whether they cause disease. The next steps are a chest X-ray and, when needed, sputum tests to check for active TB disease. With a normal X-ray and no symptoms, the diagnosis is latent TB infection, which is not contagious³. CDC guidance from 2025 rates its treatment as 90% effective in preventing disease¹. A positive skin test stays positive even after treatment, so ask for a written record of it². People with a documented positive result do not get another skin test¹. The page on positive tuberculosis (TB) test next steps explains what follows.

A two-step PPD test is two skin tests given 1 to 3 weeks apart when the first one is negative. It sets a reliable starting result for people who will be tested again over time, such as health care workers. The second test catches a reaction that only shows when the immune system is reminded by the first². A positive second test is read as an infection from long ago, not a new one⁷. The person is then checked for TB disease⁷. The page on the two-step tuberculosis skin test covers the timing.

Yes: BCG vaccination sometimes turns a PPD test falsely positive. No reliable method tells a BCG reaction from TB infection, so 2025 CDC guidance reads it as if you were never vaccinated. The blood test is not affected by BCG and is preferred for people who had it⁴. A BCG reaction generally fades over the years, but repeated skin tests may boost it again¹. The comparison of PPD vs QuantiFERON helps people who had BCG choose.

The PPD test is a skin test read after two or three days, while the TB blood test needs one visit. CDC guidance from 2024 encourages blood tests, especially for people unlikely to come back for the reading. Unlike the skin test, the blood test causes no booster effect⁴. It is also unaffected by most nontuberculous mycobacteria⁴. Blood tests may cost more than skin tests⁴. Collecting enough blood is a practical barrier in very young children⁴.

The PPD test detects most TB infections, yet it misses some and gives false positives in others. In pooled studies, it was positive in 95% of people with culture-confirmed TB disease. In low-risk groups its specificity was 85% and 86%, against 99% for the QuantiFERON-TB Gold In-Tube blood test⁸. False negatives come from a weak immune system, called anergy, or from infection in the past 8 to 10 weeks¹. A recent viral illness such as measles, or wrong placement or reading, can also cause them¹. False positives come from BCG, nontuberculous mycobacteria or wrong measurement¹. A negative TB test: what it means explains when more tests follow.

Yes: TB screening means testing people more likely to have met TB, and the PPD is one of two tests used. People at low risk generally do not need screening. Health care workers get a two-step PPD or a blood test when they start². After that baseline, health care workers without TB infection need no yearly testing unless there is an exposure or ongoing spread⁷. The page on tuberculosis testing for healthcare workers covers the rules.

These short answers cover safety, where to get tested, pain and aftercare.