00:00So, your TB blood test comes back positive.
00:03Naturally, you're concerned.
00:06TB is a dangerous infectious disease, isn't it?
00:11Well, yes, tuberculosis can be serious and untreated.
00:17Active TB disease can be fatal.
00:19But a positive TB blood test doesn't automatically mean you have active tuberculosis disease.
00:26And it doesn't actually mean automatically that you are contagious.
00:33The TB blood test is called an IGRA, which stands for interferon gamma release assay.
00:41It looks for an immune response to TB-related proteins.
00:46A positive result usually means your immune system has reacted to the bacterium.
00:51But the test cannot tell by itself whether you have active TB or latent TB infection.
01:01That distinction is extremely important.
01:05In latent TB infection, the bacteria are present in the body.
01:10But the immune system is keeping them under control.
01:14The person does not feel sick, they have no symptoms, and they can't spread TB to others.
01:23The chest X-ray is usually normal, and sputum testing, if done, does not show active disease.
01:33Active TB, on the other hand, is different.
01:37In active TB, the bacteria are multiplying, causing illness.
01:42If active TB involves the lungs or the throat,
01:46the person may be able to spread TB through the air when they cough or speak or sing.
01:53Symptoms may include a cough lasting several weeks, weight loss, fever, night sweats, fatigue, chest pain, or even coughing up
02:05blood.
02:06So when a TB blood test is positive, your doctor should not interpret that result in isolation.
02:16They will ask about your symptoms.
02:19They will ask whether you've been around someone with tuberculosis.
02:23They will ask whether you were born in, lived in, or traveled to a place where TB is common.
02:31They may ask whether you work in healthcare, shelters, correctional facilities, or other settings where TB exposure is more likely.
02:42They will also consider whether you have any condition or medication that weakens your immune system.
02:51The next step is usually a medical evaluation and a chest X-ray.
02:57In some cases, sputum testing is also needed to make sure active TB disease is not being missed.
03:07Now, what if you have no symptoms and no known risk factors?
03:13In that situation, a false positive becomes more plausible, especially if the result is close to the cutoff.
03:23This is one reason low-risk people generally should not be tested unless testing is required for work, for school,
03:34immigration, or other formal reasons.
03:38If a low-risk person has a positive result, clinicians may repeat testing or use a second type of TB
03:48test before deciding that such a person is truly infected.
03:55Sometimes the test does not come back clearly positive or negative.
03:59Depending on the test, it may be called indeterminate, borderline, or invalid.
04:07That means that the test did not give a reliable answer, and repeating the test or using a TB skin
04:15test may be more appropriate.
04:18The take-home message is this.
04:21A positive TB blood test should not be ignored, but it should also not be interpreted by itself.
04:30The meaning of the result depends on your symptoms, your exposure history, your risk factors, your chest x-ray, and
04:40sometimes sputum testing.
04:43In medicine, context is what turns a lab result into a diagnosis.
04:50I hope you enjoyed this video.
04:52If you did, like and share the video with your friends and family.
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05:00Until the next video, stay healthy and stay safe.
