<<Disclaimer: Verify this information before applying it to your situation.>>

Many thanks to those who  responded to my question about false positive
blood tests.  Most agreed that, indeed, there can be false positives, and
many respondents gave anectodal evidence.  The response that follows was
the most clearly stated.  Again, thanks to those who responded.

"Yes,  there are false positive lab tests as well as false negative
ones.  In fact, these are the two types of errors that most labs work
very had to minimize...it's nearly impossible to get rid of them
altogether.  A false positive occurs when the lab test comes back
positive (e.g., elevated levels of IGA/IGG) and the gastroenterologist
then orders a biopsy (the definitive test for celiac sprue) and it comes
back negative; that is, clean or ok.  In such a case the positive
antigen test was due to some other factor other than sprue.. and these
can be many.  Likewise, a false negative occurs when the initial test
comes back negative but a later test reveals the true existence of the
suspected disease.  This is why medical science/art rarely relies on a
single finding to draw a conclusion...or...for that matter, on a single
opinion."