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Doctor insights on: What Causes A False Positive Tb Skin Test

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Dr. Scott Lindquist
613 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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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. ...Read more

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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 ...Read more

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Could a positive TB skin test mean you always have tb?

Could a positive TB skin test mean you always have tb?

POSITIVE PPD: NO. Sometimes it is due to immunization given before. Take a chest x-Ray to find any lesion in the lungs. ...Read more

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If I have a positive TB skin test, does that mean I have tb?

Not necessarily: (+) PPD means that you have been exposed to the TB agent. It doesn't say when. So if you had the TB in the past, it still will be (+) because your body "remembers" from the previous exposure. The greatest risk is if the TB agents are latent in your body, that's why everyone with a (+) PPD will have either a complete treatment with 4 medications or a mild one with only one. Your PPD will remain (+). ...Read more

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If I had a positive TB skin test but a negative xray do I need medication? My doctor didn't say I did

If I had a positive TB skin test but a negative xray do I need medication? My doctor didn't say I did

Positive PPD: If you have a positive tuberculin test and a negative chest xray many doctors will oder a sputum culture. If you have a positive sputum treatment is indicated. However, many doctors will treat prophylactically with isoniazid for protection ...Read more

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Always had positive TB skin test last chest X-ray 5 yrs ago now have supraclavicular swelling after prednisone/cortisone possible tb? What to ask dr

Always had positive TB skin test last chest X-ray 5 yrs ago now have supraclavicular swelling after prednisone/cortisone possible tb? What to ask dr

Ask when next appt?: This could be tb, but might be one of several other infectious, musculo-skeletal, or related conditions. It needs examined by a doctor, soon. Questions the provider asks should help direct yours beyond just "what is it? " initial cxr or ct scan will likely yield more information to base questions (and treatment, if needed) on. ...Read more

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Is it normal that a TB skin test causes bleeding a lot?

Is it normal that a TB skin test causes bleeding a lot?

No but....: No, but may occur if the administration of the test is traumatic. Also may happen if you are taking medicine that has an anticoagulant effect, such as daily aspirin. Or if you have a bleeding problem. ...Read more

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Found out TB skin test positive and stressed please help?

Found out TB skin test positive and stressed please help?

Don't be: Don't be stressed. You need a chest x-ray and a screening by your doctor. At your age, if your chest x-ray is normal and you have no risk factors you may not need any treatment. If you have risk factors, treatment of latent TB has become much easier in the last year. If you are determined to have active TB you can be cured with 6 months of TB therapy. ...Read more

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A red like a bite of mosquito, is it considered positive for TB skin test?

A red like a bite of mosquito, is it considered positive for TB skin test?

Swelling important..: Redness is not important, but induration (swelling) is when reading a TB test. For normal healthy person, induration of > 15 mm is considered positive. Other clinical situations may warrant calling >10 mm of induration positive. ...Read more

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What does it mean if I have a negative TB skin test yet a positive blood one?

What does it mean if I have a negative TB skin test yet a positive blood one?

IMMUNE PROBLEM: Both tests detect prior exposure to TB. A situation of diminished immune function, called anergy, can make the skin test appear negative. If you have a positive blood test you will need to have a CXR to exclude active infection and may need prophylaxis. ...Read more

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I got a TB skin test today and the site is red and puffy. It does not itch or anything. Is it positive?

I got a TB skin test today and the site is red and puffy. It does not itch or anything. Is it positive?

Too early to tell: The TB skin test needs to be looked at 48-72 hours after it was placed. Redness at 24 hours does not mean anything. The swelling (induration in medical language) is what your provider will be looking at. ...Read more

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What to do if I have a positive on my TB skin test?

Seek out information: Most will be followed first with a chest x-ray looking for active pulmonary disease. If negative, you are likely started on one TB drug, depending on your local as treatment for latent (quiet) tb. If you are found to have active tb, you are likely started on a 4 drug program that lasts for up to a year to knock it out. Get with your doc to see. ...Read more

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If my Tb skin test came back positive, should I be worried?

If my Tb skin test came back positive, should I be worried?

Positive PPD: A positive TB skin test should be followed up with a chest xray. If both are positive for findings, one should be treated and followed by an infectious disease specialist and take medications. False positive skin tests can occur if previously vaccinated against TBor infected with TB-like organisms. Improper technique or interpretation of reaction are other causes of false positives. ...Read more

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Should I concerned that my TB skin test came back positive?

Not really: It does mean your have been exposed and will need treatment to prevent it from worsening TB is a very slow growing germ...
I would also suggest consulting a chinese medicine practitioner as many herbs are very helpful in helping the body heal itself.... ...Read more

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Can a TB skin test be positive if person had TB in the past?

Yes: Exception will be the ones who had a latent TB and received a prophylactic inh treatment for 9 months. Their reaction to tuberculin test can become negative. ...Read more

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What can be done to determine if you have positive result for TB skin test?

Different cutoffs: Positive result for TB skin test is based on the size of the swelling (induration) at the site of TB test & additional risk factors that you have for acquiring tb. There are 3 cut offs for determining positive result (5, 10 & 15mm) & each one has different criteria for being used as cutoff for your test. Talk to your doctor to find out whether your test is positive or not based on these factors. ...Read more

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My previous TB skin test was negative while current is positive. How is this possible?

True of false: This could be a true or false positive, and your doc should sort that out. People can be exposed to TB in the activities of their daily lives, and pick up a latent TB. In med school it was common for students to convert from - to + over a their time in training. You will need more testing, an may or may not need meds. ...Read more

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What do you suggest if my previous TB skin test while negative while current is positive?

Need care!: Your TB test has turned positive - this is very significant. The guidelines are very clear what needs to happen now with further diagnostic studies, including chest x-ray, and then treatment. If your primary care doctor is not comfortable caring for TB, see infectious disease or pulmonary specialist ASAP to begin evaluation and care. There are great ones in Columbus area - call for appointment now ...Read more

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Can you tell me if a TB skin test came up (borderline) positive, wouldn't it always come up the same?

No: A person can have a false negative test if they are immuno compromised, have poor nutrition etc. 10 to 15% of people with newly diagnosed lung TB come up with a neg PPD initially. A test that is borderline may be positive later. Once you have a + ppd, you normally don't need to have it repeated. ...Read more

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Will the TB skin test cause a side effect of diarriah?

Will the TB skin test cause a side effect of diarriah?

NO RELATIONSHIP: Tb skin test is an intra-dermal test where very minute amount of reagent is injected into the skin. Nothing to do with the GI system. ...Read more

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If my TB skin test ran positive but I've never had tuberculosis, does that mean I have latent tb? And do I have to take antiobiotics if I do have it?

Possible exposure.: If PPD is positive than you need a screening chest xray. If xray negative than 9 months of one med inh should be taken to prevent activation of possible dormant tb. ...Read more

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I just had my TB skin test on Thurs and I noticed my skin is a little bit elevated at the site of injection with erythema around it?? positive result??

I just had my TB skin test on Thurs and I noticed my skin is a little bit elevated at the site of injection with erythema around it?? positive result??

Depends: On the onset of redness/elevation from the time testing and the diameter of the elevated area, also if you have had BCG vaccination as a child, that can be very well a false positive test, alternate blood testing can be used, good luck ...Read more

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Can doing a TB skin test cause symptoms like fever and nausea?

Can doing a TB skin test cause symptoms like fever and nausea?

No: The TB skin test contains some proteins that are derived from killed TB bug, so there are no live bugs involved. You may have acquired an intercurrent illness at the time of testing. ...Read more

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I got redness like bruise after my TB skin test am I positive for tb?

Induration: Redness doesn't count; it has to be induration (hardness). If you gently run a ballpoint pen along your skin toward the site of the test and it comes to a stop, you may have reached the edge of the induration. You can then determine the diameter of the induration by doing the same thing from the other directions. If it's red but there's no induration, it's a negative test. ...Read more

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Can all europeans test positive for tuberculosis on the TB skin test because europeans get a vaccine for it?

No: If you get bcg (tb vaccine) you can get false positive PPD for up to 4 years. A blood test quantiferon will differentiate false positives from true positives. ...Read more

Dr. Klaus d Lessnau
1,212 Doctors shared insights

Tuberculosis (Definition)

A potentially serious infectious bacterial disease that ...Read more