Indirect tests which rely on the immune response to Borrelia are commonly used as they are simple and cost effective. The routine Borrelia diagnostic test is 2 tiered; the first test has high sensitivity and the second test has high specificity. They rely on a serological response and involve either an indirect fluorescence antibody test (IFAT) or an enzyme linked immuno-sorbent assay (ELISA), (either whole cell antigen from bacterial culture or recombinant) and if it is positive then an immunoblot/western blot (either whole cell antigen or recombinant) is done. Other diagnostic tests like the ELISPOT and MELISA rely on the T cell response when exposed to Borrelia proteins.
To ensure high sensitivity of direct diagnostic tests, blood sampling at the time point of highest fever or highest intensity of symptoms may result in a higher number of spirochetes. For instance, relapsing fever has cycling high spirochetemia resulting in high fevers (Larrson et al, 2009; Assous et al, 2009). Cultures from EM rash biopsy are most successful but not all tick bites cause an EM rash. Culture is less successful from blood or CSFand further CSF sampling requires a specialist doctor.
Indirect diagnostic tests do not discriminate between different stages of borreliosis or current active or from previous infection. The IFAT and ELISA assume the patient is immuno-competent and can synthesize the appropriate antibodies. However, this may not be the case for stage III borreliosis where there is evidence of immune dysregulation.
A prolonged IgM response is often detected which may be due to a relapsing fever Borrelia infection which can result in almost continual IgM production due to its hyper variable membrane protein expression with no iso-type switching to IgG. Immune dysfunction where immunoglobulin iso-type switching, IgM to IgG, is prevented or delayed by Borrelia burgdorferi senso lato infection in Stage III may also present with a prolonged IgM response.
In patients with EM confirmed Lyme diseases in early stages of infection with treatment there is a mixture of immunoglobulin response from IgM positive with and without serconversion to IgG, IgM negative which seroconverts to IgM (Rebman et al, 2014). With antibiotic treatment in stage 3, sera conversion from negative to positive IgG can be observed.
A false negative ELISA in the presence of clinical symptoms may also be due to immune dysfunction or due to the antigens used in the ELISA may be different to the Borrelia genospecies with which the patient may be infected. There may be decreased amounts and/or low affinity iso-types of antibodies. The western blot test is more sensitive as it detects more bacterial proteins than ELISA in the serum.
The definition of positive criteria for western blot is contested. CDC-USA have implemented 5 out of 10 bands as being positive while 2 specific bands were used prior to 1995 in the USA and presently in Germany. China presently uses 1 specific band in conjunction with clinical symptoms as being positive. In Scotland, 3/15 bands are classified as a weak positive and 4/15 bands as a positive (Mavin et al 2011). As mentioned, only if a positive result from IFAT (or ELISA) is obtained will a western blot be conducted. The western blot then needs to fulfil the CDC USA criteria of 5/10 bands to be deemed positive.
As part of the CACLD, a diagnostic pathway working group was formed to address what is the best diagnostic algorithm and to standardise the testing at a national level. Nonetheless, Australian patients continue to use overseas labs (which often include wider range of borrelia antigens in their western blot).