What are Tuberculosis Skin and Its Purpose?
Is TB a deadly disease, and who is prone to it? These are some of the questions that most people are trying to figure out. Approximately 1.3 million people die every year from TB. And one-third of the people across the globe are diagnosed with latent TB. So, a tuberculosis skin test, also known as the tuberculin test, helps determine if a person has developed an immunity to the bacterium causing TB.
Latent TB has no symptoms, and someone may have this TB bacteria in the body and not know as it doesn’t make you feel sick. Most people that breathe in this bacterium get infected. But the body can fight the bacteria and stop them from growing.
If someone had received the BCG vaccine (not applicable to the US residents), got exposed earlier, or currently has TB, this response may show in their system. Hence, the need for tuberculosis skin tests. Since TB can kill, doctors recommend taking a medicine prescription if diagnosed with TB, even if you feel okay.
Symptoms of Active TB
While some people may have LTBI that doesn’t have any signs, an active form of TB may have these symptoms:
- Coughing for three or more weeks.
- Coughing up blood
- Chest pain
- Pain while coughing or breathing
- Weight loss.
- Chills.
- Fever.
- Fatigue.
- Night sweats.
Getting a definitive diagnosis of active TB will depend on the culture of mycobacteria from a tissue biopsy. And it might take several weeks for the bacteria to grow on specialized media, as they grow very slowly.
The treatment might take six months, and a physician might prescribe certain antibiotics if the cause of TB is atypical mycobacteria. If the drug therapy doesn’t work, surgery can be an option. It may involve debridement, draining of the abscesses, and incision.
How Medical Caregivers Administer A TB Test
The tuberculosis test’s standard recommendation is to use 0.1 mL of a liquid containing 5 TU (tuberculin units) of PPD. Then you inject this into the top layers of skin (intradermally) of the forearm.
A practitioner must ensure to use a skin area free of abnormalities and away from veins.
He uses a 27-gauge syringe to make the injection. That means the target area must be underneath the surface of the skin.
There should be a pale skin elevation (a wheal) of 6mm-10mm in diameter for correct injection. And this gets absorbed pretty fast. But if there was an incorrect test administered, a health provider can perform another test in a different area away from the initial injection.
How To Read The Tuberculosis Skin Test
When a practitioner reads the skin test, he’s looking for an induration (a raised, thickened area of skin reaction). It’s best to read the skin test 48-72 hours after the injection. That’s the time when the induration size is maximal. But reading the tests after this time may underestimate the induration size, thus giving an inaccurate reading.
Reading a tuberculosis skin test helps to find the presence or absence of the bacteria and the induration. Then the practitioner measures the diameter of the induration and records it in millimeters. Please note that this measurement doesn’t include redness.
A TB reaction can result positively based on induration size, among other specific patient risk factors. If a person has a healthy immune system and has an induration greater or equal to 15mm, then it’s considered to be positive. If the induration is less than 15 mm in certain groups of people, the test is positive.
A positive TB skin test may follow with an X-ray for the chest to help determine the difference between a latent TB infection and an active TB.
Exposure to the bacteria causing TB may result in active TB disease or latent TB infection. What do these mean?
Latent TB
Though you may not have any signs or symptoms of tuberculosis, you may have latent TB. Taking a tuberculosis skin testis prudent as this may detect the bacteria. If left untreated, it may later develop into an active disease.
Active TB
People diagnosed with HIV are 15-18 times more likely to develop active TB than those without.
A physician uses a combination of meds to treat latent TB. And it might take six to nine months to treat this TB disease, which focuses on preventing the future development of active disease.
Types of TB Tests
A TB test is tolerable and rarely has an adverse reaction. The two types of TB tests used to diagnose it are blood and skin tests. While the results may not show the form of TB in the body, it helps determine the ideal treatment you need.
If you have a positive TB skin test result and show symptoms, you may be at high risk of TB exposure. A physician will most likely prescribe medications for you to relieve symptoms and clear up the infection.
But if you’re positive with low risk, he may recommend a TB blood test to confirm the diagnosis. It’s a more accurate test compared to the TB skin test.
False-Positive Result
Certain countries take a BCG vaccine to reduce the risk of developing TB. These people may have a false-positive TB skin test result.
Other Causes For A False-Positive Result:
- Incorrect test administration
- Inaccurate reading of test results
- Nontuberculous mycobacteria infection
Negative-False Results
The reasons that cause false-positive results are similar to what causes negative-false consequences. Immune system conditions such as an organ transplant can also lead to a false-negative skin test.
Someone who had previously had a TB exposure in the past few weeks may also test negative for TB.
If someone has the risk of TB exposure or has TB symptoms but tests negative, a practitioner might suggest a second skin test. And he might also offer a more accurate blood test.
In Conclusion
TB can be dangerous and claims many lives every year. It’s the 13th leading cause of death globally and second after COVID-19’s most infectious killer disease. Since those in developing countries are prone to TB, they should take a tuberculosis skin test to find if they have a mycobacterium infection and avoid spreading it. There is over 95 percent of cases and deaths in these countries.