What Is
a PPD Test?

PPD tuberculosis skin test explained. Learn what it tests for, how it works, what results mean, and where to get tested.

What the PPD Test Measures

A PPD test -- short for purified protein derivative -- is a screening tool used to detect whether your immune system has ever encountered Mycobacterium tuberculosis, the bacterium that causes tuberculosis (TB). The test works by introducing a tiny amount of tuberculin, a protein extract derived from TB bacteria, just beneath the surface of your skin. If your immune system recognizes the protein because of a prior exposure, it mounts a localized inflammatory response at the injection site that a healthcare provider can measure and interpret.

It is important to understand that the PPD test does not detect active tuberculosis disease directly. Instead, it identifies an immune memory response, meaning your body's T-cells have previously been sensitized to TB antigens. This sensitization can occur from an actual TB infection (either latent or active), or in some cases from a prior BCG vaccination commonly given in countries where TB is prevalent. The PPD test cannot distinguish between latent TB infection, active TB disease, or BCG-related reactivity on its own -- additional evaluation is always needed when a result is positive.

The PPD test is also known as the Mantoux tuberculin skin test (TST) and has been a cornerstone of TB screening programs for decades. It remains one of the most widely used and cost-effective methods for identifying individuals who may carry latent TB and could benefit from preventive treatment before the infection progresses to active disease.

Who Needs a PPD Test

PPD testing is not a routine screening for the general population. It is targeted toward individuals who have an elevated risk of TB exposure or who would face serious consequences if an undetected latent infection were to reactivate. The following groups are most commonly required or advised to undergo TB screening:

• Healthcare workers -- nurses, physicians, medical assistants, lab technicians, and anyone working in hospitals, clinics, nursing homes, or home health settings
• Childcare and education workers -- teachers, daycare staff, and school employees who work closely with children
• People starting new employment -- many employers in healthcare, food service, and congregate living facilities require TB screening as part of pre-employment health clearance
• Travelers and immigrants -- individuals who have lived in or traveled extensively to countries with high TB prevalence, including parts of Asia, Africa, Latin America, and Eastern Europe
• Close contacts of known TB cases -- anyone who has spent significant time with a person diagnosed with active pulmonary TB
• Residents and staff of congregate settings -- including correctional facilities, homeless shelters, and long-term care homes
• Immunocompromised individuals -- people living with HIV, those on immunosuppressive therapy, or those with conditions that increase the risk of latent TB reactivating into active disease

If you are unsure whether you need a PPD test, your employer or school will typically inform you as part of onboarding requirements. You can also ask your provider during a telehealth visit whether screening is appropriate based on your personal risk factors and exposure history.

How the Test Is Performed

The PPD test involves a small injection under the skin of the forearm, read 48 to 72 hours later.

The PPD test is a simple two-visit procedure. During the first visit, a healthcare provider cleans a small area on the inner surface of your forearm and uses a fine needle to inject 0.1 milliliters of tuberculin solution just beneath the top layer of skin. This is an intradermal injection, meaning the needle enters at a very shallow angle and deposits the fluid within the skin itself rather than into the muscle. When placed correctly, a small, pale wheal (a raised bump roughly 6 to 10 millimeters across) forms immediately at the injection site. This wheal is expected and confirms proper placement.

The injection itself feels like a brief sting or pinch and takes only a few seconds. Most people describe the discomfort as minimal -- significantly less than a standard blood draw or vaccination. After the injection, you should leave the site uncovered and avoid scratching, rubbing, or applying creams, bandages, or ice to the area. Washing your arm gently with soap and water is fine. A small amount of itching at the site over the following day or two is normal and does not indicate a positive result.

The critical second step is the reading visit, which must occur 48 to 72 hours after placement. You will return to have a trained healthcare professional examine and measure the injection site. This window is strict -- a test read before 48 hours or after 72 hours is considered unreliable and may need to be repeated. Plan both appointments in advance so you can return within that timeframe.

Reading Your PPD Results

When you return for your reading visit, the provider evaluates the injection site by feeling for induration -- a firm, raised, hardened area beneath the skin. This is distinctly different from simple redness or bruising. The provider measures the diameter of the induration in millimeters across the widest point of the forearm (not along its length). Redness alone, no matter how dramatic it looks, is not used to determine the result. Only the size of the firm, palpable swelling matters.

The threshold for a positive result depends on your individual risk category, not a single universal cutoff. The three standard thresholds are:

• 5 mm or greater is considered positive for the highest-risk individuals: people living with HIV, those who have had recent close contact with an active TB case, organ transplant recipients, people on immunosuppressive therapy, and anyone with chest X-ray findings suggestive of prior TB
• 10 mm or greater is considered positive for moderate-risk groups: recent immigrants from high-prevalence countries, injection drug users, residents and employees of congregate settings, healthcare workers, and children under age four
• 15 mm or greater is considered positive for low-risk individuals with no known risk factors for TB exposure

A result of 0 mm of induration -- meaning no palpable hardening at all -- is recorded as negative regardless of risk category. Your provider will interpret the measurement in the context of your personal health history and risk profile to determine whether further evaluation is needed.

What a Positive Result Means

A positive PPD result means your immune system has been exposed to TB bacteria at some point -- but it does not mean you are sick or contagious. The vast majority of people with a positive PPD have latent tuberculosis infection (LTBI), a condition in which the bacteria are present in the body but are being held in check by the immune system. People with LTBI feel completely well, have no symptoms, and cannot spread TB to others. However, without treatment, approximately 5 to 10 percent of people with LTBI will eventually develop active TB disease during their lifetime, with the highest risk occurring in the first two years after exposure.

After a positive PPD, the next step is almost always a chest X-ray to look for signs of active pulmonary tuberculosis, such as infiltrates, cavities, or enlarged lymph nodes in the chest. If the chest X-ray is normal and you have no symptoms like a persistent cough, night sweats, unexplained weight loss, or fever, the diagnosis is typically latent TB. Your provider may recommend preventive treatment -- usually a course of isoniazid for several months or a shorter rifamycin-based regimen -- to eliminate the dormant bacteria and prevent future reactivation.

It is also worth noting that false-positive PPD results can occur, particularly in people who received the BCG (Bacillus Calmette-Guerin) vaccine as children. BCG is widely administered in many countries but is not part of the routine vaccination schedule in the United States. If you received BCG and your PPD is positive, your provider may recommend a TB blood test to help clarify whether the reaction reflects true TB exposure or a vaccine-related response.

PPD Test vs TB Blood Test

In addition to the PPD skin test, there are blood-based TB tests known as interferon-gamma release assays (IGRAs). The two FDA-approved IGRAs are the QuantiFERON-TB Gold Plus and the T-SPOT.TB test. These tests work by drawing a blood sample and measuring how your immune cells respond to TB-specific antigens in a laboratory setting. Like the PPD, IGRAs detect immune sensitization to TB bacteria rather than active disease itself.

The primary advantage of a TB blood test over the PPD is specificity. IGRAs use antigens that are not present in BCG vaccine strains or most non-tuberculosis mycobacteria, which means they produce far fewer false positives in BCG-vaccinated individuals. Blood tests also require only a single visit -- there is no need to return 48 to 72 hours later for a reading. This makes them particularly practical for people with unpredictable schedules or those who may have difficulty returning for a follow-up appointment.

The PPD test, on the other hand, is generally less expensive, does not require a specialized laboratory, and has a longer track record in large-scale screening programs. It remains the preferred method in many occupational health settings and for serial (repeated) testing of healthcare workers. Your provider can help you determine which test is most appropriate based on your BCG vaccination history, risk profile, employer requirements, and practical considerations. In some cases, both tests may be used together to improve diagnostic accuracy.

Where to Get a PPD Test

PPD tests are available at a variety of healthcare settings including primary care offices, urgent care clinics, occupational health centers, local health departments, and pharmacies with clinical services. Because the test requires two in-person visits -- one for placement and one for reading 48 to 72 hours later -- it is not a procedure that can be performed entirely through telehealth. However, a telehealth visit can be a valuable first step to determine whether you need a PPD test, discuss which type of TB screening is right for you, and get an order or referral so you know exactly where to go.

The cost of a PPD test varies depending on your location, insurance coverage, and the facility you visit. Without insurance, prices typically range from $20 to $68. Many employer-required TB screenings are covered by the employer or by occupational health programs at no cost to the employee. If you have health insurance, TB screening is often covered as a preventive service, particularly if you fall into a recognized risk category. Check with your insurance plan or the testing facility in advance to understand any out-of-pocket costs.

If you need guidance on TB screening requirements for a new job, school enrollment, or travel, the providers at InnoCre Telehealth can help you understand your options and coordinate next steps. We offer same-day appointments for patients in Maryland, Washington, and Delaware, so you can get answers quickly and move forward with confidence.

Frequently Asked Questions