The main diagnostic tests (ELISA, EIA and IFA) look for antibodies to Borrelia-they measure the body's immune response to the bacteria. However, one of the difficulties is that, because Borrelia can hide in the body, the immune system can't always detect it and make antibodies. This means that there's a danger of false-negative results. In fact, one study showed the ELISA test to be wrong as much as half of the time (J Clin Microbiol, 1997; 35: 537-43).
Lyme disease practitioners often use a back-up test called the Western Blot, which detects the DNA of Borrelia itself. However, this, too, is not fool-proof, as the DNA may not show up for weeks after the infection, if at all.
Although new lab tests, such as IVIAT and QRIBb, are claimed to be more accurate, there is still no totally reliable laboratory diagnostic test. The absence of a definitive diagnosis simply serves to fuel the controversy as to what LD really is, and how best to treat it.
One high-tech tool is a SPECT (single photon emission computed tomography) brainscan. Its high resolution images can reveal characteristic abnormalities in the brains of LD victims, in particular 'cerebral vasculitis', believed to be the underlying cause of many Lyme disease symptoms.