Depending upon the infection, the accuracy/quality of the testing may vary. So, you need to know which tests are useful for which infections.
Ideally, if you test for the DNA of an infectious agent and find it, you can be pretty sure you have it. Unfortunately, these are not available or accurate for all infectious agents. The typical test is called a PCR, polymerase chain reaction test.
https://www.genome.gov/10000207/polymerase-chain-reaction-pcr-fact-sheet/
Another way of finding an infection is to culture it. Or look for it in cerebral spinal fluid. These aren't typically done.
Then there are antibody titers. Most doctors will look for IgM titers, which suggest an acute infection when elevated, they drop after the acute infection is over.
IgG and IgA levels rise and can denote chronic infection. Historically, doctors have interpreted high IgG values as evidence if a past infection and typically, once one has had an infection, IgG levels will be higher than normal for life. So, many doctors will look at high values and miss the fact that they're high because the infection is still causing IgG antibodies to be created. The threshold of what's considered high will vary from infection to infection and lab to lab.
I'd had several doctors blow off my infections, but my ME/CFS specialist, who'd treated AIDS patients with weird infections for years, looked at my titers and said "I know what we were all were taught in med school, that high IgG is indicative of past infection, but they were wrong. Your titers are high and you do have these infections." He also ran PCR tests where he could to confirm his interpretation.
You may also have an immune system that is not responding properly to fight infections. The attached article discusses a deficient response to EBV. I was in this situation ehere several previous tests looked negative, because my immune system wasn't making all of the correct antibodies. My specialist ran some other tests, and then a PCR and found it.
Most doctors interpret using generalities and aren't up on the intricacies of each test. Its best to research each infection to see what is known about testing. You can post your results here, along with the ranges and labs, to see what others have learned about the tests you've had done.
Identifying and treating an infection you weren't aware you had can really help you.
