Aplisol is a skin test solution used to detect tuberculosis (TB) infection. It contains a purified protein derived from the bacteria that cause TB, and it’s injected just under the skin of the forearm to trigger a visible immune response in people who have been exposed to the disease. The FDA approves it specifically as an aid in detecting infection with Mycobacterium tuberculosis.
Aplisol doesn’t diagnose active TB disease on its own. Instead, it identifies whether your immune system has encountered TB bacteria at some point, a condition known as latent TB infection. A positive result means your body recognizes TB proteins, which prompts further evaluation, typically a chest X-ray and medical assessment, to determine whether you have an active or dormant infection.
How the Skin Test Works
A healthcare provider injects a small amount of Aplisol into the top layer of skin on the inside of your forearm, a technique called the Mantoux method. The injection creates a small, pale bump that disappears within minutes. Over the next two to three days, your immune system responds to the injected proteins if it has encountered TB bacteria before. That response produces a firm, raised area of skin called induration at the injection site.
You need to return to your provider between 48 and 72 hours after the injection to have the result read. A trained healthcare worker measures the induration (not redness or swelling, just the firm bump) in millimeters across the forearm. If you don’t return within 72 hours, the test is no longer valid and you’ll need to schedule a new one.
What the Results Mean
A skin test result isn’t simply positive or negative for everyone. The size of induration that counts as positive depends on your personal risk factors for TB. The CDC uses three cutoff points.
- 5 mm or more is positive for people living with HIV, anyone who has recently been in close contact with someone who has active TB, people with certain chest X-ray findings suggesting prior TB, organ transplant recipients, and others on immunosuppressive medications.
- 10 mm or more is positive for people born in countries where TB is common (including Mexico, the Philippines, Vietnam, India, China, Haiti, and Guatemala), people who live or work in nursing homes, homeless shelters, or correctional facilities, children under 5, people with diabetes, severe kidney disease, or certain cancers, and people with low body weight.
- 15 mm or more is positive for people with no known risk factors for TB.
A measurement below the relevant cutoff, or 0 mm, is considered negative. These tiered thresholds exist because the consequences of missing a TB infection are more serious in people whose immune systems are compromised or who are more likely to have been exposed.
Who Gets Tested With Aplisol
TB skin testing is commonly required for employment in healthcare, education, and food service. It’s also standard for people entering correctional facilities, homeless shelters, and long-term care settings. Beyond workplace screening, providers use Aplisol to test people who have symptoms of TB (a persistent cough lasting three weeks or more, fever, night sweats, unexplained weight loss) or who have been in close contact with someone diagnosed with active disease.
People who have previously had a severe reaction to a TB skin test, such as blistering, ulceration, or tissue death at the injection site, should not receive Aplisol again. The same applies to anyone with a known allergy to any of the product’s components. If you’ve already had a documented positive skin test in the past, repeating it is generally unnecessary and could cause an unnecessarily strong local reaction.
BCG Vaccination and False Positives
Many people born outside the United States received a BCG vaccine in childhood, which protects against severe forms of TB in young children. Because BCG is made from a related bacterium, it can cause a positive skin test reaction even in people who were never infected with TB. This is one of the most common sources of confusion with Aplisol results.
The CDC recommends that a positive skin test be taken seriously regardless of BCG history, since the vaccine’s effect on skin test results fades over time and many people from countries with high BCG vaccination rates are also at genuine risk of TB exposure. When BCG history complicates interpretation, providers often turn to a blood test (called an interferon-gamma release assay) instead, which is not affected by prior BCG vaccination.
Aplisol vs. Other TB Skin Tests
Aplisol is one of two tuberculin skin test products available in the United States. The other is Tubersol. Both contain purified protein derivative and work the same way. In clinical studies, the two products give similar results for most patients. However, switching between them during repeat or serial testing can occasionally produce discordant results, where someone tests positive with one product and negative with the other, not because their infection status changed, but because of minor differences between the products. For this reason, consistency matters if you’re being tested regularly for a job or other requirement.
What Happens After a Positive Result
A positive Aplisol test does not mean you have active TB or that you’re contagious. Most people with positive results have latent TB infection, meaning the bacteria are present in the body but dormant. You feel completely healthy, you can’t spread TB to others, and you may never develop active disease.
After a positive skin test, the next step is usually a chest X-ray to check for signs of active lung disease. If the X-ray is normal and you have no symptoms, you’ll typically be offered treatment for latent TB to prevent it from becoming active later. The risk of latent TB progressing to active disease is about 5 to 10 percent over a lifetime, but treatment reduces that risk substantially. Treatment courses for latent TB range from three to nine months depending on the regimen your provider recommends.
If the chest X-ray shows abnormalities or you have symptoms, further testing, including sputum samples, helps determine whether you have active TB disease, which requires a longer and more intensive course of treatment.