I was hired in October 2007 and had to take a TB test along with my other intake paperwork. The following year I got a notice that I had to take a skin test (you know, they stick you with a pin, you come back in two days and they look to see if there’s a reaction), and again last year the same thing – a skin test.
Yesterday I got a memo that said if I’ve been working since July 2007, I have to have a Quantiferon blood test, for which I have to make an appointment. If I started working before July 2007, I can have the skin test. The blood test is somewhat more of an inconvenience for me, but I don’t really care. I’m just curious what the difference is.
I called to make my appointment for the blood test, and mentioned that I’d had the skin test the previous two years. The woman I talked to tried to insinuate that I’d done the wrong thing and had been in violation in 2008 and 2008, when I had done exactly as I had been told. I asked what the difference between the two tests was and why some employees took one and some the other, and she said she had no idea.
There was another number on the memo for questions about the test, and I just called that one. The woman who answered that phone was more clueless than the other. I repeated that I didn’t really care which test I took, but I wanted to know the difference. Was one test more accurate? Were there different strains of TB that were going around in July 2007? She said “One’s a blood test and one’s a skin test.” She said that three times. I assured her that I knew the difference between skin and blood. :rolleyes: She finally said, “I just think you’re asking more philosophical questions than I can answer.”
I don’t think those are philosophical questions. Can someone answer them?
Hi sigmagirl
the blood test is more accurate as it tests for antibodies specific to TB, unlike the skin test which tests for a range of antibodies.
CDC have more information Fact Sheets | Testing & Diagnosis | Fact Sheet - Recommendations for Human Immunodeficiency... Clinics | TB | CDC
Hope this is helpful
Yes, that was interesting. It doesn’t explain the “July 2007” division, but it helps. Thank you.
The skin test is the Tuberculin Skin Test (TST, aka Mantoux).
Advantages:
Cheap
Disadvantages
Require a follow up appointment for reading
Reading is prone to subjective examination
TB vaccine causes a false positive
The Quantiferon (aka interferon gamma release assay) is new, and much better.
Advantages:
Tuberculosis vaccine does not affect it
Not prone to subjectivity
Disadvantages:
Expensive
So, I don’t know why they have a cutoff at 2007. Possibly a cost saving measure?
Side note: The vaccine is rarely used in the US, except in some high-risk cases, so this may not be a factor.
Get the blood test.
More sensitive, more specific, and safer for you.
Mantoux has a chance of local reaction, ulceration and scarring, as well as a fair chance of being falsely positive or negative, as well as a reasonable rate of user failure (it requires intradermal injection).
http://www.seacoastmedical.com/Forms/ProductInfo/Tubersol.pdf
Info about the product used in the Mantoux.
Purely guessing at a reason:
I assume the skin test is cheaper? What are the chances of multiple false negatives with the skin test?
My guess is that if you have been around long enough to have been repeatedly tested for TB using the skin test with negative results every time they are going to assume the chance that you really have it is too low to care about. However (again guessing) if you have been hired recently they don’t have the assurance of multiple negatives and want the more accurate (and presumably more expensive) test so that they can feel comfortable with the results.