In the UK, laboratory tests for Borreliosis consist of a two-tier system which detects antibodies to Borreliae. The first of these is an Enzyme Linked Immunosorbent Assay (ELISA). This test superseded the Immunoflorescence Assay (IFA) and is the most commonly used serodiagnostic screening method for Lyme borreliosis.

If the ELISA is positive or equivocal, the sample is then tested with an Immunoblot, also known as a Western blot. Western blot, ELISA and PCR (polymerase chain reaction) can be performed on blood or cerebrospinal fluid (CSF), which is obtained via a lumbar puncture. However, antigen capture in CSF can be extremely elusive; reportedly CSF yields positive results in only 10-30% of patients cultured. Therefore, the diagnosis of neurologic Borrelial infection should not be excluded solely on the basis of a negative CSF antibody analysis.

The detection of Borrelia DNA using PCR can also be performed. This type of molecular test can be useful on joint fluids in cases of suspected Lyme arthritis, and on biopsies from suspected skin infection. It isn’t normally used for blood samples as Borreliae are rarely present in the bloodsteam after the early stage of infection. PCR isn’t favoured for CSF.

All methods of testing have their limitations and can produce both false-positive and false-negative reactions. Antibodies may not be present for the first few weeks after infection so a negative test does not exclude infection. A second sample taken 2-4 weeks later may then go on to show seroconversion. In late stage disease, patients can be seronegative although this is considered a rare phenomenon.

False-positive results can occur if the patient has antibodies to Bb without having a current infection (e.g. people who are occupationally exposed, such as foresters, or people who are recreationally exposed to tick bites).

The significance of any result, negative or positive, should be interpreted carefully by clinicians in the overall context of a patient’s clinical findings and tick-exposure history. Other conditions such as glandular fever, syphilis, or certain neurological illness can also trigger a false-positive reaction.

Other techniques for testing are in development but their clinical usefulness are the subject of debate and have yet to be adequately established.