There are many types of ELISA (enzyme-linked immunosorbent assay) or EIA (enzyme immunoassay) tests used in laboratory medicine. The general principle involves fixing an antigen of interest to a surface, then applying a test specimen over this surface. If an antibody to that antigen is present it will bind to the surface. This antibody can be linked to an enzyme, which produces a color change or other detectable signal.
Antibody capture EIA is a sophisticated, complex test that has proved useful in the diagnosis of many infectious diseases (e.g. rubella, measles, and toxoplasmosis). Antibody capture EIAs are particularly sensitive in demonstrating IgM responses early in illness. Reasons for this increase in sensitivity are: specific antibody isotypes in the patient’s specimen are bound to the solid phase by the capture antibody allowing the specific antibody-antigen reaction to occur in the absence of competing isotypes; soluble antigen is added in excess (allowing the antigen and antibody to react in antigen excess); and the antibody capture EIA measures the proportion of specific to total antibody of a given isotype (which may be detectable earlier than simply measuring specific antibodies as in an ELISA test).
The Imugen laboratory utilizes antibody capture EIA methodology as part of its Lyme Antibody Analysis. It is an antibody test method for demonstrating Borrelia burgdorferi antibody early in the immune response and it has been shown to perform well in detecting Lyme (B. burgdorferi) infection.
Lyme antibody capture EIA is an antibody isotype specific test that involves the affinity purification of the specific immunoglobulin isotypes (i.e. IgM, IgG or IgA) from the patient specimen, then detects the presence of antibody (of that isotype) to B. burgdorferi. Values for IgM, IgG and IgA are individually reported.
Antibody capture EIAs are also useful in demonstrating local antibody production in CSF. A CSF:serum ratio for IgM, IgG and IgA can easily be attained without adjustment of serum or CSF concentrations. In addition, since the antibody capture assay is sensitive to low levels of antibody, the proportion of total to specific antibody measured is not affected by the lower antibody levels inherently found in CSF.
Lyme antibody capture EIA is an isotype specific test. When the Lyme antibody capture EIA is utilized, the IgM response can usually be detected within the first weeks following onset of symptoms. The IgA response is usually detected earlier than the IgG response. The IgG response is often not detectable for 3-4 weeks. The detection of multiple isotypes by Lyme antibody capture EIA is highly indicative of infection with B. burgdorferi.
The pattern of an immune response to Lyme infection has been well characterized. Patients with early, mid, or late-stage infection exhibit rather typical patterns of serologic findings. The Lyme antibody capture EIA, when combined with immunoblotting, provides detailed characterization of a patient’s serologic response, assisting the clinician in detecting infection and staging Lyme disease.
The Imugen laboratory freezes and archives positive specimens for one year. The acute specimen is retrieved, thawed and re-tested on the same test run as the follow-up specimen. Concurrent specimen analysis can determine if the specific antibody titer is increasing or decreasing.