Tuberculosis (TB) is a potentially serious infection that usually occurs in the lungs. The bacteria that causes TB is spread through the air from common things like sneezing and coughing. Unfortunately, that means you are more susceptible to get infected with TB in the winter months. The good news is there are tests that can help determine whether or not you’ve contracted tuberculosis: a TB blood test and skin test. Although the Centers for Disease Control and Prevention (CDC) has provided guidelines on how to use an Interferon Gamma Release Assay or IGRA blood test, a skin test is still the standard testing method in most health care facilities.  A purified protein derivative (PPD) test or a TST (Tuberculin Skin Test), is a simple test your doctors can use to help diagnose you with TB. Read more to learn about the PPD test and whether you need to take it.

What Is a PPD Test?

A Mantoux Tuberculin skin test gives you clear answers on your TB status. It can help doctors determine if you have Tuberculosis. It does not diagnose disease, just that you have exposure. Think of a Tuberculin Test as being an allergy test. A doctor injects a PPD protein (called Tuberculin) into your skin and leaves it there for 2-3 days. If your body identifies and reacts to it in 2-3 days, it means you must have been exposed to tuberculosis bacteria. The test cannot be read earlier than 2 days from the time of injection.

What Is The Fastest Way To Get A PPD Test?

A Tuberculin test involves two visits with your doctor – during the first visit, the doctor injects PPD (Tuberculin) into your skin. During the second visit,  they check the skin to see how your body responds to the tuberculin protein. It takes two to three days for doctors to measure the response.

The fastest way to get this testing done is in 48 hours. Then, doctors check your response to the test at 72 hours, after which you need to wait before the test can be re-done on a different part of the skin.

Important Things To Know About Testing

First, you always want to make sure that your doctors’ office will be open at 48 hours from the injection time so that the test result can be read. Or before 72 hours. If you miss that window between 48-72 hours, the test result becomes void.

If you miss the time slot, you’ll have to wait at least 7-10 days for another skin test. And this can become an issue if you need the test for a job or college. So, we recommend that you have the test read between 48-72 hours.

Secondly, many doctors’ offices will not read the test if someone else has done it. They may agree to read it. However, there’s a bunch of hoops that you’ll have to jump through, which will be time-consuming for you.

Thirdly, many doctors’ offices will read it as positive or negative because traditionally that is how it was meant to be read. However, science has progressed and now you need to know the size of the reaction in millimeters. If the reaction size is missing, it can become an issue with Federal and State requirements such as for purposes of Immigration. Also, all subsequent medical decisions for PPD will be based on the size in millimeters and your medical and demographic history. At Statcare, we do PPD Testing all week long. Our providers always measure and note the millimeters.

What Happens When You Get a PPD Test?

To take the test, a doctor will swab the inside of your forearm with an alcohol solution. Then, they will administer the PPD shot under the top layer of your skin. It should be quick and relatively painless (for a shot). Your doctor will give you a bandage for the injection site. Remove the bandage after a few minutes. Allergy to band-aid glue is common and you want to be sure that nothing interferes with your test. After that, you go home and wait for 48-72 hours.

The second part of a PPD test (NOT to be confused with a 2 step PPD test) happens 48 to 72 hours later. You’ll return to your doctor to get the results. The doctor or nurse will examine the injection point and give your results. They might also ask about your country of birth, medical history, or prior PPD results. You’ll then get your results. If you experience any redness or irritation during those 48 – 72 hours, it may not be directly related to your TB skin test. Don’t panic, just wait until you can see your doctor or nurse to get an accurate reading on your reaction.

Reading TB Test Results

When you arrive for the second part of your Tuberculin test, your doctor will look at the skin around the injection. The standard guidelines are to measure the area that looks reddish or pinkish (called Erythema) and record its size in millimeters. Then, the area has to be felt by the examiner’s fingers to detect any raised, thickened and firm skin inside the red or pink area. This hardened skin is called induration and its size also needs to be recorded in millimeters.

Induration is often raised and has an edge. It takes a skilled, trained doctor to administer an accurate reading, which is why it’s important to be selective when choosing a doctor for your TB test. Always choose a medical provider that does this test routinely.

Although retail pharmacies might offer a PPD test, their staff may not have the same kind of nuanced understanding of the test results to ensure the most accurate reading possible. Pharmacists aren’t trained during their schooling to read PPD results, but it is a regular part of a doctor’s medical school training. TB is too serious of infection not to choose the most highly skilled medical professional to help you with testing.

Getting a Positive Test – What It Means

There are a few things to keep in mind if you get a positive Tuberculin test. First, tuberculosis progresses in two stages: latent and active. And all latent TB infections do not always convert into active TB.

It is good to think of Latent TB as being a sleeper cell of a terrorist bacteria called Mycobacterium Tuberculosis.  The tuberculosis bacteria get inside your body and immediately go into hiding, living inside the very cells that fight infections – the white cells. The TB bacteria can thus go undetected for years. Tuberculosis bacteria also multiply ever so slowly, thus evading detection by your bodies’ troops.

This latent TB phase can last days, weeks, months or years. Latent TB means that you have a TB infection, but the bacteria are not active yet or causing symptoms. According to the Mayo Clinic, about 2 billion people in the world have latent TB. It also isn’t contagious, but it can turn into active TB at any time, so it’s still important to keep an eye on it.

Active TB

On the other hand, active TB means that the bacteria started dividing and growing inside your tissues. Typically, the TB bacteria need a lot of oxygen, so they prefer living inside lung tissue where fresh oxygen is always available. Active Tb means you are contagious, and you will experience symptoms. Some symptoms of active TB include:

  • Coughing that brings up phlegm
  • Cough that lasts three or more weeks
  • Coughing up blood or blood-tinged sputum
  • Chest pain, especially while breathing or coughing
  • Unintentional weight loss
  • Fatigue
  • Fever, esp. towards the evening
  • Night sweats
  • Chills
  • Loss of appetite

Unchecked, TB can also affect other parts of your body including kidneys, spine, and brain. It is important to talk to your doctor immediately after a positive skin test result to get a treatment plan in place.


What Does a Positive TB Test Look Like?

Indurations that indicate a positive PPD test look different for different kinds of people. Your previous health-related issues, plus your lifestyle can both affect your positive reading. For a healthy person who has a normal immune system, an induration greater than or equal to 10 mm is positive.

False Positives

Sometimes the PPD is read as positive because of skin inflammation. If blisters are present on that person’s arm, the medical professional needs to determine if it was an allergic reaction to the protein (hypersensitivity) or truly a positive result.  It is quite common to have an allergic reaction to the glue in the tape. This glue upon the skin causes inflammation of the skin (contact dermatitis) which may have nothing to do with the underlying PPD injection. The provider must have medical knowledge and the right clinical experience to diagnose TB.

Problems With Tuberculin Testing

Not everyone has a typical immune system. For those, the test gets a little more specific. For example, if an induration measures 4 mm or more, the USCIS considers it a positive test for purposes of immigration forms.

Guide to Skin Reaction Size

5mm And Above

An induration (size of skin reaction) of 5 mm can be indicative of TB for people who:

  • Have suppressed immune systems
  • Are HIV positive
  • Have seen changes on chest x-rays that are consistent with the previous TB
  • Are recipients of organ transplants or on steroids, chemotherapy drugs or TNF-Alpha-blockers

10mm Or More

If an induration measures 10 mm or more, it is positive if you:

  • Are a recent immigrant (within 5 years) from a place with a high prevalence of TB
  • Have recently spent more than a month in areas with a high prevalence of TB
  • Are a resident or an employee working in a high-risk area (including hospital and urgent care staff)
  • Use IV drugs
  • Have kidney disease, diabetes, stomach surgery, certain cancers, Body Mass Index of less than 18.5%, silicosis.
  • Under the age of 5.

15 MM

An induration of 15 mm or more is positive in a low-risk person who would otherwise not need PPD testing for screening for TB.

As you can see, there is a lot of personal medical history that goes into reading a positive result. If you want to talk to your doctor and ask questions about your skin test, you should seek out a testing center that you can trust, with doctors who will give you accurate and complete answers. Statcare doctors can help you through treatment options and offer all the resources you need right at your appointment. No need to follow up or see additional doctors. You’ll get everything you need during your visit.

An important note on positive test results: your induration will likely not go away for 3-4 weeks. That is normal. If it becomes red and starts creating ulcers, talk to your doctors.

What to Do After a Negative Test?

If there is no induration present at the site of the test, you most likely do not have TB. However, there are factors, such as viral infections, vaccinations, certain diseases, or medicines you might be consuming, that could generate a false negative for a Tuberculin test. People who are on chemotherapy treatments, have the AIDS virus, or use steroids can experience a false negative result. Be sure to answer all your doctor’s questions honestly when giving your medical history so they can accurately read your test results.

What Is A 2-Step PPD Test?

A 2-Step PPD test helps eliminate false-negative results. It is simply two tests done within two months of each other. Repeating the test after a 7-day interval boosts the response. Most healthcare jobs require a 2-step test.

Follow Up Tests for TB

Your care does not stop once you are read your PPD test results. If you test positive, there is no need to take the test again. Once you have been exposed to Tuberculosis, the TB skin tests will always come back positive for the rest of your lifetime. The follow-up conversations you’ll have with your doctor will include medication and symptoms management. TB responds to different medications in a unique way, so getting treatment as soon as possible will help you maintain a healthy lifestyle. You’ll want to schedule 2 chest x-rays, one year apart, to monitor your lung function after your initial diagnosis. Women who are pregnant will also need special care, so keep in touch with your doctor as you manage your TB.

On the other hand, a negative result doesn’t mean that you will remain negative forever. Everyone should consider taking an annual PPD test, but especially if you fall into one of the more vulnerable categories listed above. At all Statcare locations, you can get an accurate PPD test read by a doctor you trust, for only $40.

So, Should You Get Tested?

If you live in NYC, the answer is simple: yes. Exposure to Tuberculosis is common in NYC. Even if you got the BCG vaccine when you were younger, the protection fades away as you get older. If you think you may have been infected, been around someone who has TB, or recently traveled to high-risk areas, definitely ask for a TB PPD test near me as soon as possible. Come to Statcare for your 2 step PPD test as well as all the answers and treatment options you need. We are here to help.

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