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How To Read Tb Skin Test

Who Performs A Tb Test

Reading Tuberculin Skin Test

Any healthcare provider who is specially trained in performing and assessing the results of a TB skin test can perform the test.

A healthcare provider called a phlebotomist usually performs blood draws, including those for a TB blood test, but any healthcare provider who is trained in drawing blood can perform this task. They then send the sample to a lab where a medical technologist prepares the samples and performs the test.

Understanding Your Test Results

If you have a positive test result and you have symptoms or are considered at high risk of TB exposure, youll likely be prescribed medications to clear up the infection and relieve symptoms.

If youre low risk and have a positive test, your doctor may recommend a TB blood test to confirm the diagnosis. The TB skin test is less accurate than the blood test, so you could have a positive skin test and a negative blood test.

How It Is Done

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 TB antigen is put under the top layer of skin. The fluid makes a little bump under the skin. A circle may be drawn around the test area with a pen.

Do not cover the site with a bandage. You must see your doctor 2 to 3 days after the test to have the skin test checked.

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How To Read A Tuberculosis Skin Test

This article was medically reviewed by Mandolin S. Ziadie, MD. Dr. Ziadie is a board certified Pathologist in South Florida. She specializes in renal, transplant, and pediatric Pathology and has over 12 years of experience. She earned her medical degree from the University of Miami School of Medicine in 2004 and completed her fellowship in Pediatric Pathology at Childrens Medical Center in 2010.wikiHow marks an article as reader-approved once it receives enough positive feedback. This article received 16 testimonials and 89% of readers who voted found it helpful, earning it our reader-approved status. This article has been viewed 932,073 times.

A tuberculosis skin test is also known as the Mantoux tuberculin test. This test measures your immune system’s response to the bacteria that causes tuberculosis. Your results will be interpreted by your doctor a couple of days after the test. If you’re curious about how to read a tuberculosis skin test, this article will guide you through the process, but remember: the test must be read by a trained professional. You can interpret the test yourself, but the result needs to be documented by a medical professional to ensure proper treatment and/or follow-up.XTrustworthy SourceCenters for Disease Control and PreventionMain public health institute for the US, run by the Dept. of Health and Human ServicesGo to source

What Is A Two

The Mantoux Tuberculin Skin Test Wall Chart

The two-step TB skin test involves a first step and reading as described above, and then it is repeated again, at least 1-4 weeks later if the first TB skin test was negative. This step also requires you to return in 48-72 hours to have it read. If either the first or second step is positive, you will need a medical examination and chest x-ray to be sure you are not sick with active TB. For people who may need to have routine TB screening because of their work or other risk factors, only the initial testing should be a two-step. Once a baseline is established, further TB skin testing should only require one-step.

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When Should I Know The Results Of My Tb Test

It takes 48 to 72 hours to complete a skin TB test. Once you have your second visit with your healthcare provider, theyll be able to tell you if your skins reaction indicates that you may or may not have a TB infection.

In most cases, you should get the results of your TB blood test within one to two days, though it could take longer.

Normal And Critical Findings

PPD Skin test Interpretation Based on CDC Guidelines

The result of the PPD test is positive or negative. However, the size of the induration diameter cutoff for the test to be positive is based on certain risk factors.

As the diameter cutoff increases, the sensitivity of this test declines, and the specificity increases. For instance, the sensitivity of this test for 5 mm diameter cutoff positivity is the highest, whereas, 15 mm diameter cutoff positivity is more specific.

Induration of 5 mm and more is considered positive in:

  • Immunosuppressed individuals
  • HIV infected individuals.

An induration of 10 mm or more is considered positive in:

  • Immigrants from endemic/high prevalence countries in the last 5 years.
  • High-risk area employees and residents. For example, prisons, nursing homes, and homeless shelters.
  • Injection drug abusers.
  • Children less than four years of age.
  • Chronic medical conditions that increase the risk of tuberculosis include diabetes, kidney failure, malignancy, etc.
  • Infants/Children/adolescents exposed to high-risk categories.

An induration of 15 mm or more is considered positive in:

  • Always considered positive in any person. Healthy individuals without any risk factors for TB.
  • Patients who do not meet any of the above criteria

Positive PPD Skin test

If the infection risk is very high, the PPD test need not be repeated. The positive PPD test is usually followed by TB symptom assessment, physical exam, and chest radiograph.

Negative PPD Skin test

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Adverse Reactions To Tsts

  • Severe adverse reactions to TSTs are considered rare.
  • Severe reactions include anaphylaxis , severe swelling, heavy blistering, or “weeping” of the skin.
  • If an individual does not have documentation of a severe adverse reaction but provides a convincing verbal report, document the severe adverse reaction and do NOT administer another TST.
  • Substitute a TB blood test for the TST if it is available in your area.
  • Mild itching, swelling, or irritation are more common and are not a contraindication to future testing.
  • Individuals should be instructed to avoid scratching or scrubbing the site, to keep the site clean and dry, and to avoid putting lotions or adhesive bandages on it.
  • A cold compress may be helpful.
  • How Do Physicians Interpret Skin Test Results

    Positive PPD Test (Tuberculin Skin Test) – Interpretation, Diagnosis, and Tuberculosis

    The basis of the reading of the skin test is the presence or absence and the amount of induration . A physician will measure the diameter of the induration transversely to the long axis of the forearm and recorded in millimeters. The area of induration around the site of injection is the reaction to tuberculin. It is important to note that redness is not measured.

    A tuberculin reaction is classified as positive based on the diameter of the induration in conjunction with certain patient-specific risk factors. 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 , the test is also considered positive.

    In some groups of people, the test is considered positive if induration less than 15 mm is present. For example, an area of induration of 10 mm is considered positive in the following groups:

    • Recent immigrants from high-prevalence areas
    • Residents and employees of high-risk areas
    • IV drug abusers
    • Children under 4 years old
    • People who work with mycobacteria in laboratories

    An induration of 5 mm is considered positive for the following groups:

    • People with suppressed immune systems
    • People with changes seen on chest X-ray that are consistent with previous TB
    • Recent contacts of people with TB
    • People who have received organ transplants

    People infected with other types of mycobacteria other than Mycobacterium tuberculosis may also have false-positive TB skin tests.

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    How A Tb Skin Test Works

    A TB skin test measures your immune systems response to a purified protein derivative solution injected under your skin. PPD is a protein that comes from the bacteria that causes TB Mycobacterium tuberculosis.

    Its not live bacteria, and it wont make you sick. If youve ever been exposed to the TB bacteria, your skin will react to the antigens by developing a firm, red bump at the site of the injection within three days.

    How a TB blood test works

    In most cases, if youve been infected with TB, blood cells from your blood sample will release a protein called interferon-gamma when mixed with antigens derived from Mycobacterium tuberculosis in a laboratory.

    To conduct the tests, laboratory scientists mix your blood sample with antigens and controls and measure the reaction using a method called immunoassay. Theyll interpret your results as negative, positive or indeterminate.

    Next Steps After A Positive Test

    A positive skin test will usually be followed by a chest X-ray. This can help determine the difference between active TB disease and latent TB infection. Your doctor will look for white spots that indicate areas where your immune system is responding to bacteria.

    There may be other changes in your lungs caused by TB disease. Your doctor may decide to use a CT scan instead of a chest X-ray because a CT scan provides images of much greater detail.

    If the images indicate TB is present, your doctor may also order tests on your sputum. Sputum is the mucus produced when you cough. A lab test can identify the type of TB bacteria causing the infection. This helps doctors decide which medication to prescribe.

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    What To Think About

    • The results of a tuberculin skin test alone cannot confirm active TB. Other tests, such as a chest X-ray, sputum cytology, and sputum culture, may be done to confirm active TB 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 .
  • 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 may indicate a TB infection that occurred a long time ago or a previous BCG vaccination.
  • About 5% to 10% of people who have inactive TB will develop active TB at some time in their lives.footnote 1 The chance of developing active TB is higher in children, older adults, and people with an impaired immune system.
  • No more tests are needed for a person with a negative tuberculin skin test who has no symptoms of active TB and no history of being exposed to TB.
  • Some people do not react to a tuberculin skin test even if they have tuberculosis. Conditions such as active TB, cancer, or acquired immunodeficiency syndrome do not always respond normally to the TB antigens. In these cases, other skin tests may be done. If there is a skin reaction, then the tuberculin skin test is probably correct. But if there is no reaction, the person’s immune system is likely to be too weak to respond normally to the tuberculin skin test.
  • What Is The Tuberculosis Skin Test

    Core Concepts

    The tuberculosis skin test determines if someone has developed an immune response to the bacterium that causes tuberculosis . This response can occur if someone currently has TB, if they were exposed to it in the past, or if they received the BCG vaccine against TB . Estimates indicate that one-third of the world’s population has latent TB, and around 1.3 million people worldwide die of TB each year. The tuberculin test or PPD test are other names for the tuberculosis skin test.

    The tuberculin skin test is based on the fact that infection with M. tuberculosis bacterium produces a delayed-type hypersensitivity skin reaction to certain components of the bacterium. Medical professionals extract the components of the organism from TB cultures and are the core elements of the classic tuberculin PPD . This PPD material is used for skin testing for tuberculosis. Reaction in the skin to tuberculin PPD begins when specialized immune cells, called T cells, sensitized by prior infection, are attracted by the immune system to the skin site where they release chemical messengers called lymphokines. These lymphokines induce induration through local vasodilation leading to fluid deposition known as edema, fibrin deposition, and attraction of other types of inflammatory cells to the area.

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    Bcg Vaccine And The Mantoux Test

    The role of Mantoux testing in people who have been vaccinated is disputed. The US recommends that tuberculin skin testing is not contraindicated for BCG-vaccinated persons, and prior BCG vaccination should not influence the interpretation of the test. The UK recommends that interferon- testing should be used to help interpret positive Mantoux tests of over 5mm, and repeated tuberculin skin testing must not be done in people who have had BCG vaccinations. In general, the US recommendation may result in a larger number of people being falsely diagnosed with latent tuberculosis, while the UK approach has an increased chance of missing patients with latent tuberculosis who should be treated.

    According to the US guidelines, latent tuberculosis infection diagnosis and treatment is considered for any BCG-vaccinated person whose skin test is 10 mm or greater, if any of these circumstances are present:

    • Was in contact with another person with infectious TB
    • Was born or has lived in a high TB prevalence country
    • Is continually exposed to populations where TB prevalence is high

    Screening Education And Recommendations

    Education and competency validation can help ensure you stay up-to-date with new TB skin test interpretation. Results of my short survey indicated the need for staff education. After discussions with the leadership team, education and training are now provided to current and incoming staff to increase accuracy of TB skin test interpretations and decrease the risks of false-negatives.

    Safe patient care requires that all nurses be aware of their organizations policies and procedures by reviewing them periodically and staying current with new guidelines. For example, the 2005 Centers for Disease Control and Prevention guidelines recommended that all U.S. healthcare personnel working in medium-risk settings with the potential for ongoing TB transmission receive baseline screening and annual testing. The most recent updates from 2019 include the following:

    • Baseline TB screening with symptom evaluation and an individual risk assessment.
    • TB skin test or IGRA screening for anyone without a documented history of TB.
    • In the absence of ongoing transmission or a known exposure, no requirement for routine serial testing at any interval after baseline.
    • If not contraindicated, encourage treatment for all healthcare workers with latent TB.
    • Annual symptom screening for untreated healthcare personnel with latent TB.
    • Annual TB education for all healthcare workers.

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    British Columbia Specific Information

    Tuberculosis, also known as TB, is a serious disease. TB is caused by bacteria that spread through the air when a person with contagious TB coughs, sneezes, sings, or talks. TB usually affects the lungs, but can also affect other parts of the body like glands, bones, joints, kidneys, the brain, and reproductive organs.

    For more information on TB, including testing and home isolation, see HealthLinkBC File #51a Tuberculosis , HealthLinkBC File #51b Sputum Testing for Tuberculosis , and HealthLinkBC File #51c Home Isolation for Tuberculosis . For more information about TB, including information about TB clinics and programs, visit BC Centre for Disease Control Tuberculosis.

    When Should I Call My Doctor About Tb

    Tb Skin Test Read

    If you have symptoms of TB , such as a persistent cough, chest pain and fever, or think youve been exposed to someone with an active TB infection, its important to see your provider as soon as possible.

    TB can be deadly if its not properly treated. Most cases of TB can be cured if you take antibiotics as directed by your healthcare provider. Both active and latent TB should be treated, but the type and medications and how long you need them are different if you have active vs. latent TB.

    A note from Cleveland Clinic

    TB testing and screening are essential for public health. Since TB can be deadly and spreads from person to person easily, its important to get tested if you have symptoms, are at high risk for developing active TB or are at high risk of being exposed to the infection. Once you know your results, your healthcare provider will let you know if you need to undergo further tests. Dont be afraid to ask your provider questions. Theyre here to help you.

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    The Latest Interpretation For Mantoux Test Results

    According to the guidelines published by Centers for Disease Control and Prevention in 2005, the results are re-categorized into 3 parts based on their previous or baseline outcomes:

    • Baseline test: 10 mm is positive 0 to 9 mm is negative
    • Serial testing without known exposure: Increase of 10 mm is positive
    • Known exposure:
    • 5 mm is positive in patients with baseline of 0 mm
    • 10 mm is positive in patients with negative baseline or previous screening result of > 0 mm

    Classification Of Tuberculin Reaction

    The results of this test must be interpreted carefully. The person’s medical risk factors determine at which increment of induration the result is considered positive. A positive result indicates TB exposure.

    • 5 mm or more is positive in
    • An HIV-positive person
    • Persons with recent contacts with a TB patient
    • Persons with nodular or fibrotic changes on chest X-ray consistent with old healed TB
    • Patients with organ transplants, and other immunosuppressed patients
  • 10 mm or more is positive in
  • Recent arrivals from high-prevalence countries
  • Injection drug users
  • Mycobacteriology lab personnel
  • Persons with clinical conditions that place them at high risk
  • Children less than four years of age, or children and adolescents exposed to adults in high-risk categories
  • 15 mm or more is positive in
  • Persons with no known risk factors for TB
  • A tuberculin test conversion is defined as an increase of 10 mm or more within a two-year period, regardless of age. Alternative criteria include increases of 6, 12, 15 or 18 mm.

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