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Use: The test is useful in the diagnosis of spotted fever group rickettsial infections.
Antibody reactivity to Rickettsia rickettsii antigen should be considered Spotted Fever group reactive. Other organisms within the group include R. akari, R. conorrii, R. australis and R. sibirica. This test is preferred for the acute or convalescent phase of disease. Acute and convalescent titers are often necessary. IgG serum endpoint titer of ≥1:64 is suggestive of infection at an unknown time and may be a sign of either past infection or early response to a recent infection. IgM titer of ≥1:64 is regarded as probable evidence of recent or ongoing infection. A four-fold or greater increase in titer between two serum samples drawn 1-2 weeks apart and tested in parallel is the best serologic indicator of a recent rickettsial infection.
Limitations: This test is preferred for the acute or convalescent phase of disease. Acute and convalescent titers are often necessary. The CDC does not use IgM results for routine diagnostic testing of Rocky Mountain Spotted Fever, as the response may not be specific for the agent (resulting in false positives) and the IgM response may be persistent from past infection.
This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.
Methodology: Semi-quantitative indirect fluorescent antibody (IFA)
