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Doctor insights on: What Does A Negative Tb Test Injection Look

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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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What does a negative TB test look like?

What does a negative TB test look like?

Doc: Either your blood test igra is negative or your skin testing does not show any "bump". This should always be checked by a professional since even health care workers report false results. Best to check with a doc and not pa or np or nurse. ...Read more

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I got TB test injection in an open wound, is this bad? Should i get retested?

I got TB test injection in an open wound, is this bad? Should i get retested?

Yes: A TB (tuberculosis test, or ppd) should be placed on the underside of the forearm, on normal appearing skin. I can't imagine why it would've been placed within a wound, but it should be retested, because it couldn't be properly interpretted within abnormal skin. ...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.

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. ...Read more

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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. ...Read more

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Got a TB test today. There is a large very slightly swollen red spot around the injection sight. Is this bad?

Size of red area: does not matter. The elevated area is measured and the results are based on this measurement. The nurse will be paying attention to the elevation only. Take care. ...Read more

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What do a positive and negative TB test look like?

TB Tests: I bet you could google image that question. A positive reaction is read after 48 hours from the test. It would be a raised redness greater than 5 mm in circumference. ...Read more

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If i tested negative from a TB test and had been around someone who tested positive am i at risk of contracting tb?

TB risk: Yes, the PPD test is not 100%. You might want to get it repeated a month later to see if it is booster positive. Of course it is also possible that you didn't catch it. Many doctors are around people with TB a lot and never catch it. ...Read more

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When you take TB test and no bubble pops up is it negative?

A positive: Tb test is associated with elevation you can feel at the injection site -- not likely to be a discrete bubble. Redness doesn't count -- you have to feel something. ...Read more

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When you get a TB test and no bubble pops up does that mean its negative?

Yes: If there is no raised area which measures at least 5 mm in diameter the test should be considered negative. ...Read more

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How long would it take for TB test marks to go away? Mine came back neg but the mark went from unremarkable to large and red after 4 days now. Thx.

TB Test: there can be several reasons why a TB test takes longer to reactt..If you do have a large reaction as you describe you should go back to your doctors office to show it to them as theymay decide it is a delayed positive test ...Read more

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TB test: neg >72 hrs but now large lump as time goes on? How long for mark to go away?

TB test: neg >72 hrs but now large lump as time goes on? How long for mark to go away?

Negative, give time: As long as there was no hardened lump at the infection site within that first 72 hours that was greater than 15mm (or less if you have risk factors), you are still considered negative. It can take some people up to a week or so for the redness and swelling to recede. Try ice several times a day to help with any swelling. ...Read more

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Hi, i recently had a TB test. It looks round and red but no bump. It was read as negative by nurse buy after 5 days, the redness is still there.

Hi, i recently had a TB test. It looks round and red but no bump. It was read as negative by nurse buy after 5 days, the redness is still there.

No bump = negative: A PPD TB skin test is where one needle injects a tiny amount of material under the skin. It is used to check for exposure to tb. The "bump" is measured, and any redness is not measured unless it is raised above the normal skin surface. A "bump" is positive if 5, 10, or 15mm, depending on the patient's circumstances. If positive or if worried, a blood test is done. Redness resolves in a week or so. ...Read more

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I got a tb test its itching and red. Size of a quarter maybe but it doesn't seem to be swollen..pos? Neg?

I got a tb test its itching and red. Size of a quarter maybe but it doesn't seem to be swollen..pos? Neg?

Allergy to ppd: Some people get a 'reaction' like that to a ppd-but it's not indicative of a positive TB test-instead it's an allergy to the material used for the test. A doctor or trained professional can look at it and determine if it's positive based on 'firmness' (we call it induration) under the skin where the ppd was placed. Itchy and red skin is something else. If it's bad, some hydrocortisone cream helps ...Read more

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Took a TB test last monday & the nurse said it was negative on wednesday but now I have a red spot should I worry?

Took a TB test last monday & the nurse said it was negative on wednesday but now I have a red spot should I worry?

Not reversible: It is common for people to have some allergy to the components of the test medicine. The reaction for positive test is specifically the bump felt and not the redness. It will go away. ...Read more

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I am a medical assistant and had my TB test come back positive but cxr negative. Is there any follow up I should do?

I am a medical assistant and had my TB test come back positive but cxr negative. Is there any follow up I should do?

Yes: For a person with a positive PPD skin test and a negative chest x-ray, if he had a BCG vaccine in the past, he can do a quantiferon TB blood test to see if he was exposed to real TB or just to the BCG shot. If he never had a bcg, he can talk with his doctor to decide if he should take inh prophylaxis against tb. If it is not sure if he truly truly was positive on the skin test, he can repeat it. ...Read more

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If i take Benadryl (diphenhydramine) a day after i got the TB test will it interfere with it? (make it positive/negative)

No effect: The reactivity of the tuberculin test relies on immune factors not allergic responses. Benedryl will have no effect on that process. ...Read more

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I have this cough for 10 months now, medical tests including TB test are all negative. Antibiotics didn't help either. Please what could be wrong?

I have this cough for 10 months now, medical tests including TB test are all negative. Antibiotics didn't help either. Please what could be wrong?

Persistent cough?: You have had a persistent cough for ten months. If you are living with other human beings who do not have a similar cough you can be pretty confident that you don't have a very contagious condition. Think about cough secondary to post nasal drip, asthma, reflux. You should go see a pulmonary disease doctor. He will help you find out what's going on. Good luck. ...Read more

Dr. Klaus d Lessnau
1,207 doctors shared insights

Tuberculosis (Definition)

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