Interpretation

This test detects reactivity to the group-specific rickettsia. For example, antibody reactivity to the Rickettsia rickettsii will also react with other organisms within the spotted fever group.

IgG

≥1:256:

-Serum end point titers of ≥1:256 are considered presumptive evidence of recent or current infection by organisms of appropriate rickettsial antigen group.

<1:256 and ≥1:64:

-Single serum end point titers ≥1:64 and <1:256 are suggestive of infection at an undetermined time and may indicate either past infection or early response to a recent rickettsial infection.

-A 4-fold or greater increase in IgG titer between 2 serum specimens drawn 1 to 2 weeks apart and tested in parallel is considered presumptive evidence of a recent or current infection.

-In patients infected with organisms within the rickettsial groups, IgG antibody is generally detectable within 1 to 2 weeks of onset of symptoms, peaking within 1 to 2 months and declining thereafter. Following prompt antimicrobial treatment, titers generally decline below detectable levels within 8 to 11 months. With relapse, prior immunization, or delayed antibiotic treatment, IgG levels may remain elevated for more than a year postonset.

IgM

≥1:64:

-Titers of ≥1:64 are considered presumptive evidence of recent or current infection by organisms of appropriate rickettsial antigen group.

<1:64:

-Titers <1:64 suggest that the patient does not have an acute rickettsial infection.

-IgM class antibody is transiently detected within 1 to 2 weeks of onset of symptoms, usually declining rapidly within 3 months following prompt antibiotic treatment. These levels will also be elevated for an extended period with relapse, prior immunization, or delayed antibiotic treatment.