Under which conditions can tests be false negativ, after a long time
Jul 12, 2007
Hi Dr. Bob,
I already asked you this question and I also aked it to some laboratories. Unfortunately, the answers I received there did not adress my question. You are basically the only person I still expect to get some useful answer from. Synopsis: More than one year ago, I had a possible risk exposure due to unprotected sex. Since then I had shingles (Herpes Zoster) and develped a lactosis intolerance and a thrombocytopenia. My test, which was made 4 weeks ago was negative. Then: Whoohoo -> :| -> :S -> :(. Because, I read that the specificity is only 0.5%. (Side-note: I am an engineer) So, I started to calculated my probability of being positive, given the shingles and the thrombocytopenia. Under conservative assumptions I got almost 50%! :( -> 8((. Is it really that possible (0.5%) that I would get a false negative result in my case (luckily, I have no other illnesses)? I really appreciate your answer and it would help me a lot. Mad engineer
Ps: I read your short CV. I really wish that as virally enhanced person or not, I could leave such a footprint on earth and make a difference. You should consider putting this information on wikipedia. I am going to donate.
Response from Dr. Frascino
Hello Mad Engineer,
I certainly hope you are a better engineer than medical biostatistician! Your 50% calculated probability is way, way, way off base!
Here are a few facts:
1. The vast majority of cases of shingles have absolutely nothing to do with HIV.
2. The vast majority of cases of thrombocytopenia have absolutely nothing to do with HIV.
3. There is no such thing as "lactosis intolerance." As for lactose intolerance, it is not related to HIV.
4. Your negative ELISA greater than one year after your potential exposure is definitive and conclusive. HIV is not your problem. No way, no how. If you don't believe me, get a rapid HIV test. The results will be available within 20 minutes. With the sensitivity and specificity of these tests, the chances you would have two false-negative tests become so remote as to become immeasurable and essentially nonexistent.
As for Wikipedia, well, if they would like the information, they are welcomed to it!
Thanks for your donation (www.concertedeffort.org).
Be well. (Yes, indeed, you are well.)
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