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Doctor insights on: Normal Tb Skin Test Results

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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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Tb I had my skin test - redness 40 mm I will do the chest xray tomorrow! But am I contagious? What are the side effects of the treatment for TB?

Tb I had my skin test - redness 40 mm I will do the chest xray tomorrow! But am I contagious? What are the side effects of the treatment for TB?

If you are: Coughing, you are able to spread the disease. They may try to culture to see for check for variants. Standard drugs are inh/ethambutol. Duration of therapy is long. Side effects not too troubling.

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

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.

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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.

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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??

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

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TB skin test done. Today I can hardly notice anything on arm just a small dot that's left. Is this normal? Never even had a small bump when it was don

TB skin test done. Today I can hardly notice anything on arm just a small dot that's left. Is this normal? Never even had a small bump when it was don

Negative result: If you have ever been exposed to TB (by having it yourself or being close to someone who has), then your body will react to the TB skin test and make a big bump. The fact that your body didn't react means that you have never been exposed to TB and is a negative result! Have a medical professional read the result 48-72 hours after the TB test was applied!

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Got a TB skin test 10 hours ago, large red area has appeared abd gotten bigger and it looks swollen and is very sore. Normal or not?

Got a TB skin test 10 hours ago, large red area has appeared abd gotten bigger and it looks swollen and is very sore. Normal or not?

TB test: It is probably a local reaction and not necessarily a positive especially this early. Sometimes if the test is given too deeply it can cause bruising or you have a slight allergic reaction to the preservative especially if you have had one recently before this one.

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Tb skin test negative, quentform TB test negative, bone marrow biopsy results indicative of TB (reacts to ziehl niehlssen), PCR negative. How come?

No...actually: The zn stain is a broad stain for acid fast bacilli of which mycobacterium tuberculosis is one of many. The specific tests like quantiferon or the pcr test are against you having tb. The culture is the "gold standard" but you will need to wait for it. It might turn out be a cousin of TB and that too will grow out of culture. Stay on TB meds until they are certain of the AFB positive organism.

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Can induration on TB skin test be deep?

No: Induration produced by TB skin test is a raised bump.

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Can a TB skin test be read 24 hours later?

No: It is recommended to wait for at least 48 hours before interpreting the size of the swelling arising at the site of the TB test. This is because the swelling continues to increase for the first 48 hours & that is how this test has been standardized. Please make sure that you do not get your test done on a thursday, so the 48 hours time point won't come over a weekend.

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Can I take a shower while doing a TB skin test?

Can I take a shower while doing a TB skin test?

Yes: Your normal bathing habits will not have any effect on the test & your friends will appreciate it.

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After how many days does a TB skin test disappear?

3-5 days: The peak reaction usually occurs in the first 2-3 days. Most will resolve within 5 days. This can vary depending on the size of the initial reaction.

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How frequently should I get two-steps TB skin test?

Not frequently: Unless you are exposed in your job or it is needed for your job. Some health care workers get it yearly.

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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.

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Can a person acquire an immunity to the TB skin test?

Can a person acquire an immunity to the TB skin test?

No: Fortunately not or we would not be able to perform this test on more than one occasion.

Dr. Klaus d Lessnau
1,207 Doctors shared insights

Tuberculosis (Definition)

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