What does a positive TB test look like?

Nurses General Nursing

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Hi, got a good one for ya all tonight. I went Tuesday morning to get my first of two injections of TB for a new job. I'm to go back tomorrow to get it read. Now I've had this same test two years in a row for school physicals. But this time there is a reddish pink mark around the injection site that doesn't blanch much. I ran my finger along the skin and it's only slightly raised, barely detectable. I'm paranoid because one patient I worked with during my respiratory observation back in October was suspected to have TB because while she was in for pneumonia and had infection she also spit up some blood when they had her give a sputum sample to be tested. Any help would be appreciated.

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I had the same slight red raised bump today but it was a negative test. The Public Health Nurse that inspected it told me that the MA went to deep when she was giving me the shot. Go Figure.

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I just went through two Mantoux sticks for my volunteer assignment here in the hospital. I had a positive stick back in my teens, so I talked quite a bit with the nurse who was administering the tests. A positive can only, according to her, be determined by measuring induration, or swelling. Erythema, or redness, is inconsequential to the exam. This is good, since I got quite a bit of redness that took more than 6 weeks to go away entirely. I probably have a bit of a sensitivity to the carbolic acid they use to stabilize the tuberculin.

Anyway, they're looking for a distinct edge to the swollen bump. They'll then measure the diameter of the induration, and if it's wider than (what is it, 5mm?) then perhaps you're positive. Anyway, it's the swelling, the induration, and not the redness.

Oh, and when I tested positive for the tuberculin, I went in for a chest film which was negative, and I was fine.

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ChrisA said:

Anyway, they're looking for a distinct edge to the swollen bump. They'll then measure the diameter of the induration, and if it's wider than (what is it, 5mm?) then perhaps you're positive. Anyway, it's the swelling, the induration, and not the redness.

chris, you're correct....5mm of induration; if positive, cxr looking for tubercles.

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Chris, if you have had a + Mantoux in the past, you should not be taking Mantoux tests anymore. Not only are the results meaningless (once positive, always positive), but, as you mildly experienced, you can react negatively to the PPD at the site.

I've been positive for many years, and my physician told me many years ago that I should definitely NOT allow anyone to give me any future skin tests because it's possible to react so strongly that you actually slough tissue and have permanent damage at the test site.

At least, that's what my doc told me. If I'm wrong or the rules have changed, I'll be happy to be corrected.

Apart from that, yes, it's induration that counts in "reading" the results, not erythema.

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Good Lord, elkpark, thanks for the info. I'll have to check in on that.

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Specializes in Nurse Scientist-Research.

My parents were/are missionaries so when I was 2 yrs old I was given BCG to prevent me from contracting TB. I was told all through childhood not to take the PPD as I would be positive anyway. Said it until I was blue in the face until I started my first nursing job. They insisted, I didn't really know better (certainly didn't know about the sloughing thing) and I took one. It wasn't a horrible experience but I did have a 12mm induration which was thankfully documented. I've been x-rayed for every new job ever since. What gets me still is every time I go in for my annual check (I just have to fill out a checklist as long as I stay at the same job) I get told how I shouldn't be reactive. "Those BCG's are only good for 20 years" I get told with varying degrees of attitude. Maybe mine has worn off now, I don't know. Just please don't give me grief about it!! I always offer to be retested, I believe they think it's just another hospital employee trying to get out of a needle. Thank God I saved those employee health records from my first job!

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Specializes in NICU, PICU, educator.

If it gets really red and itchy, you can be allergic to the preservative in it...I have to have thermasil free. I really thought it was positive, but that is what it was.

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BittyBabyGrower said:
If it gets really red and itchy, you can be allergic to the preservative in it...I have to have thermasil free. I really thought it was positive, but that is what it was.

That's right Bitty babygrower,

The ppd can be itchy to some. They forget about it and scratch it which makes it more swollen and the reading tend to be false. When you think that you didn't scratch it then once it's more than 5 mm in diameter thats def. positive.

Lucky for me I had a BCG when I was a baby (coming from a developing country) I nursed many many TB patients in my life, checked me Mantoux often and reading was always neg.

Remember not to scratch once taking the Mantoux, it's damn itchy.

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Specializes in HIV/AIDS, Dementia, Psych.
elkpark said:
Chris, if you have had a + Mantoux in the past, you should not be taking Mantoux tests anymore. Not only are the results meaningless (once positive, always positive), but, as you mildly experienced, you can react negatively to the PPD at the site.

I've been positive for many years, and my physician told me many years ago that I should definitely NOT allow anyone to give me any future skin tests because it's possible to react so strongly that you actually slough tissue and have permanent damage at the test site.

At least, that's what my doc told me. If I'm wrong or the rules have changed, I'll be happy to be corrected.

Apart from that, yes, it's induration that counts in "reading" the results, not erythema.

You're right about not getting any more Mantoux tests after a positive. The reaction can be so bad that you can lose your limb!

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I have had lots of TB tests in the past and nothing happened. I just got a TB test today and about 8 hours after the shot, my whole arm is very sore and I have a big red spot that is raised. My mom told me that it will be ok, and that I am just worrying too much. Is my mom right?

I also found out that a patient in the nursing home I worked in was TB positive (not sure if it was active) but I came into contact with him a lot, not knowing he was positive.

Am I just freaking out for no reason??:uhoh21:

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You'll know when it's read; there's no way to say one way or another here, even if that were allowed. There are several factors to consider in determining if a reaction is positive or not.

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