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Doctor insights on: What Can Cause A False Positive Tb Test

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Can weed cause a false positive TB test?

Can weed cause a false positive TB test?

No: Have not heard about that, no relationship., .

Dr. Scott Lindquist
609 Doctors shared insights

Mycobacterium Tuberculosis Infection (Definition)

Mycobacterium tuberculosis is an infectious organism that spreads by droplets coughed out by an infected person. Infection is established initially in lungs, but can spread within lungs & to other body parts, or can become latent, with reactivation occurring years to decades later. With effective treatment, it can be completely eliminated although drug resistant ...Read more


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Tb test site bled right after injection. Can this give a false positive? Obviously, it was not intradermal. Don't answer if you don't know how to.

Tb test site bled right after injection. Can this give a false positive? Obviously, it was not intradermal. Don't answer if you don't know how to.

Check with your doc: The test was not appropriately administered. You want to ask your doc for a new one. Or get the igra blood test which is better anyway. The skin test is almost in the museum of history of medicine.

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Why would someone born in the Netherlands get a false positive on a PPD TB test?

Why would someone born in the Netherlands get a false positive on a PPD TB test?

Usually unknown: The reasons for false positive PPD are unknown. There is speculation that it could sometimes result from past infections with various TB-like bacteria. Such infections aren't very common, but they are equally frequent in the Netherlands as anywhere else. As long as the tested person is outwardly healthy and definitely does not have tuberculosis, this is nothing to worry about.

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Can DPT booster done at the same time affect TB test so that it is interpreted as false positive? In addition, TB test site bled right after injection

PPD: First- DTP injection does not affect the response to TB test second- TB test is placed intra dermally - which means no bleeding at injection site.

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Why would someone born in india get a false positive on a PPD TB test?

Easy: What determines a false-positive test? Either not measuring induration, or that it was due to prior bcg, which seldom lasts more than 5 yrs. If someone has a negative PPD it means either that they do not have a focus of inactive tuberculosis or that they are anergic (incapable of reacting due to deficiency in immune mechanisms).

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2 TB skin tests. Bumps measured 15cm. RN stated I possibly have LTBI & ordered QuantiFERON Gold in-tube test. Could anything cause a false positive?

2 TB skin tests. Bumps measured 15cm. RN stated I possibly have LTBI & ordered QuantiFERON Gold in-tube test. Could anything cause a false positive?

Not at 15cm, but...: The bump is more likely 15mm, because 15cm is 6 inches and HUGE. A 15mm bump on a screening test is big but may still be a false positive (a screening test means the patient has NO symptoms of tuberculosis). If a patient has contacted somebody with TB, or has current symptoms, she likely has a true positive unless her bump is due to past BCG vaccine. The Quantiferon-TB blood test is very accurate

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What percentage test false-positive for tb?

What percentage test false-positive for tb?

TB skin test isn't: Perfect test. A false-positive test may happen if you've been vaccinated with the bacillus calmette-guerin (bcg) vaccine. This tuberculosis vaccine is seldom used in the United States but is widely used in countries with high TB infection rates.

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How accurate is this test :quantiferon-tb gold? And can they show up like false positive? I have test done and don't like the results I see. Scared

QFT Gold: Quantiferon gold can give false negetive or positive. Blood samples must be processed within 12 hours after collection while white blood cells are still viable. Test is not reliable among persons recently exposed to m. Tuberculosis, and in immunocompromised persons. False positive results can occur with m. Szulgai, m. Kansasii, and m.Marinum.

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Can you have a false positive TB gold blood test?

Can you have a false positive TB gold blood test?

Yes: Every test ever made can have false positives, some more common then others.

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If a person had TB as child and underwent treatment for it, could he have a false positive TB skin test as an adult?

If a person had TB as child and underwent treatment for it, could he have a false positive TB skin test as an adult?

Yes: Once you had a positive PPD test, it will stay positive whole your life. Chest x-ray, what you need to do every few years.

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Could a TB skin test be false positive if the needle was to deep? My arm bled after the test and now that its healing I have a large purple bruise

Could a TB skin test be false positive if the needle was to deep? My arm bled after the test and now that its healing I have a large purple bruise

Wouldn't accept it: The test is standardized to represent the reaction to material places between layers of your dermis (skin) and would become invalid if it went too deep and bled. It deserves repeating. I would worry that it could be falsely negative if the test material dissipated into deep tissue. That could lead to a delay in proper treatment. A false positive would be unlikely& need eval

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Could you tell me what happens if I have a positive TB test?

Latent vs active TB: If you have a + PPD then you will be screened to determine if you have TB infection or TB disease. The physician will obtain a medical history, physical examination, chest x-ray, & any other pertinent lab tests.

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How long is TB test takes and what is the symptoms and causes of tb.

How long is TB test takes and what is the symptoms and causes of tb.

What test was done?: Skin test takes 48 hours and needs to be interpreted by a qualified professional, i.e.; whoever placed the test. Blood draws can give the answer in 1-2 days and may be indicative of past infections. Tb is an infection caused by a bacteria. It requires multiple antibiotics for months to eradicate. If there is an active infection of the lungs, it can be highly contagious. Symptoms are variable.

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How difficult must an induration be to be considered positive TB test?

PPD: It is not about hardness of the induration it is about the size of the area of induration. It is harder than surrounding skin.

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Will TB test be positive if one had primary complex?

Yes, I think so.: It may not be an absolute certainty, but I would advise the physician of the fact that there was a primary complex diagnosed and treated (assuming it was) either before the TB test or at the time of results if they are positive. I have never had positive results, but I was told that I had a primary complex - I always tell them the history just to be informationally complete. Best!

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I haven't had a TB test in years and yesterday the spot flared up. What could cause this to happen?

I haven't had a TB test in years and yesterday the spot flared up. What could cause this to happen?

Seroconversion: If you are referring the spot where you had a TB test done within the past 1 - 3 days, then it is an indication that you have either seroconverted or that you have develop a sensitivity to the testing. When a person seroconverted, it important for them to have further evaluation, usually a chest xray. If it is a spot from a TB test years ago, it does not have anything to do with the TB test.

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What does a positive TB test mean?

Chest X ray: It is possible to have active TB with very little symptoms especially early on. However, it is more than likely that you carry the germ for TB in a dormant form, this is called latent tb. No symptoms are expected with latent tb.

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What does a positive TB test look like?

What does a positive TB test look like?

Skin test: If you had a PPD skin test and you have no risk factors, a positive test is when after 48 to 72 hoursyou have swelling in the site and redness that measures more than 15 mm, it is considered a positive tb. Test.

Dr. Klaus d Lessnau
1,207 Doctors shared insights

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