Mark Carroll's Journal

I can tell you from dealing with a lab being set up for blood donor testing that it can be horrendously expensive. The reagents for particular diseases also must be well maintained temperature-wise, and the lab always runs confirmation tests if there is any question about the results.

I would imagine that for animal testing it's the same.

The testing machines these days are incredible and massively sophisticated. If they are calibrated properly and well maintained, false testing is not common.