These results have been interpreted using CDC criteria. Serological results must be correlated with clinical findings.
Serological studies are the primary means of Lyme disease (LD) diagnosis. The CDC recommends that all previously undiagnosed possible LD cases be tested by a two-tier algorithm:
1) All sera are to be initially tested with an anti-B. burgdorferi antibody enzyme immunoassay (EIA).
2) All EIA positive or equivocal sera are then confirmed with B. burgdorferi antibody immunoblot (IB) assays.
a) IgM & IgG IBs in first month of infection (i.e. during the EM period), or
b) IgG only thereafter.
The sensitivity of the CDC two-tier algorithm ranges from 40% in the first weeks of infection to nearly universal seropositivity in untreated Late LD. The IgM IB is necessary to maximize sensitivity early in the infection, but is prone to false positive results; a positive IgM IB alone after the first 1 – 2 months of illness is most likely a false positive result. (That is, the IgG IB should also be positive beyond Local Early LD.) When reviewing LD serology results, it is important to remember two things:
1) LD patients can remain seropositive for months or years, even after successful treatment. Repeat testing when reinfection is suspected is therefore of little clinical utility.
2) There are no published data that support the appearance and disappearance of individual bands on IBs as a tool in diagnosis. It is thus more useful to rely on the interpretation of an IB, and not on the individual bands reported.
Note that IgM IB data will now always be provided when the EIA is positive or equivocal regardless of the stage of infection. The clinician should therefore interpret positive IgM/negative IgG IB results carefully in cases clearly beyond the early erythema migrans phase.
When early LD (i.e. the erythema migrans phase) is suspected and the LD antibody screen test is negative, retesting once in 2-4 weeks is recommended: performance of IBs in this scenario offers little benefit. Beyond the early phase, a negative EIA result confidently rules out LD in the immunocompetent patient; IBs are of little benefit in this scenario and can lead to misdiagnosis and unneeded treatment.