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Test Code RMSF Spotted Fever Group Antibody, IgG and IgM, Serum

Reporting Name

Spotted Fever Group Ab, IgG, IgM, S

Useful For

An aid in the diagnosis of spotted fever group rickettsial infections

Specimen Required


Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL

Seattle Children's Hospital Note:

Collect 1.0 mL whole blood in a Red top.

Specimen Type


Specimen Minimum Volume

0.2 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 14 days
  Frozen  14 days

Day(s) and Time(s) Performed

Monday through Friday; 9 a.m.

Performing Laboratory

Mayo Medical Laboratories in Rochester

Method Name


Method Description

Substrate slides containing antigen wells for measuring antibodies to both groups of Rickettsia (spotted fever and typhus) are obtained from Focus Technologies, Inc. (Cypress, CA). The indirect immunofluorescence assay (IFA) is a 2-stage "sandwich" procedure. In the first stage, the patient serum is diluted in yolk sac diluent. The diluted serum is placed on the slide in contact with the substrate and incubated. Following incubation, the slide is washed in buffered saline, which removes unbound serum antibodies. In the second stage, each antigen well is overlaid with fluorescein-labeled antibody to human IgG or IgM. The slide is incubated allowing antigen-antibody complexes to react with the fluorescein-labeled antihuman IgG or IgM. After the slide is washed, dried, and mounted, it is examined using fluorescence microscopy. Positive reactions appear as rickettsial bodies exhibiting bright apple-green cytoplasmic fluorescence against a background of orange to red yolk sac matrix. Semiquantitative end point titers are obtained by testing serial dilutions of positive specimens.(Package insert: Rickettsia IFA IgM, Focus Technologies Inc., Cypress, CA)

Reference Values

IgG: <1:64

IgM: <1:64

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

86757 x 2

LOINC Code Information

Result ID Test Result Name Result LOINC Value
84342 Spotted Fever Group Ab, IgG, S 5313-2
84346 Spotted Fever Group Ab, IgM, S 5315-7

Testing Algorithm

See Acute Tick-Borne Disease Testing Algorithm in Special Instructions.

Reject Due To


Mild OK; Gross reject


Mild OK; Gross reject