What does the Babesia microti IgG antibody by indirect immunofluorescence assay test measure?

Why is Babesia microti IgG antibody by indirect immunofluorescence assay measured?

IgG distinguishes established or past infection from the earliest acute phase. A high or rising IgG titre supports recent B. microti infection, whereas a stable low titre is more consistent with prior exposure in an endemic region. Because IgG can persist long after clearance, it cannot by itself establish active disease; it is read alongside IgM, smear, and PCR, and is most useful when paired acute and convalescent specimens demonstrate seroconversion.

Reference ranges

Standard reference

Reported as a reciprocal endpoint titre. IgG rises later than IgM and persists for months to years; commonly cited positivity thresholds range from 1:64 to 1:256 depending on the laboratory and the surveillance definition applied. The reactive cut-off and any high-titre threshold are defined by the performing laboratory.

Functional medicine optimal

Non-reactive in an unexposed individual. A persistent low-level IgG in a resident of an endemic area may reflect resolved past infection rather than current disease and is not, in isolation, an indication for treatment.

Units

titre (reciprocal endpoint dilution)

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.