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Test ID: SFGP Spotted Fever Group Antibody, IgG and IgM, Serum

Reporting Name

Spotted Fever Group Ab, IgG, IgM, S

Useful For

Aiding in the diagnosis of spotted fever group rickettsial infections

Clinical Information

Species of Rickettsia are small (0.3-0.5 mcm x 1-2 mcm) obligately intracellular bacteria (Proteobacteria). They have a gram-negative cell wall structure. Rickettsiae are found in arthropod hosts for at least part of their life cycle.


Rickettsial infections in the United States are caused by 2 major groups within the genus Rickettsia: spotted fever group and typhus fever group. The spotted fever group includes Rickettsia rickettsii (Rocky Mountain spotted fever), Rickettsia akari, Rickettsia conorii (Boutonneuse fever), Rickettsia australis (Queensland tick typhus), and Rickettsia sibirica (North Asian tick typhus). The typhus fever group includes Rickettsia typhi (murine typhus; endemic typhus) and Rickettsia prowazekii (epidemic typhus).


R rickettsiae is the most common rickettsial species encountered in the United States and is transmitted through a tick vector (Dermacentor species or, less commonly, Rhipicephalus sanguineus). Following a 2- to 14-day incubation period, patients most commonly present with fever, chills, and myalgia. A maculopapular rash typically appears 2 to 5 days after fever onset, though approximately 10% of patients will not develop a rash. Antibodies to the spotted fever group agents are detectable within 7 to 10 days after illness onset. Demonstration of either seroconversion or a 4-fold change in IgG-specific antibody titers in acute and convalescent serum samples is consistent with acute or ongoing disease.


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.



Titer results of 1:256 and above:

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


Titer results from 1:64 to 1:256:

-Single serum end point titers from 1:64 to 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 collected 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 post-onset.



Titer results of 1:64 and above:

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


Titer results below 1:64:

-Titers below 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.

Report Available

Same day/1 to 3 days

Day(s) Performed

Monday through Friday

Clinical Reference

1. Walker DH, Bouyer DH: Rickettsia: In: Murray PR, Baron EJ, Jorgenson JH, et al, eds. Manual of Clinical Microbiology. 8th ed. ASM Press; 2003:1005-1014

2. Helmick C, Bernard K, D'Angelo L: Rocky Mountain spotted fever. Clinical laboratory and epidemiological features of 262 cases. J Infect Dis. 1984 Oct;150(4):480-488

3. Centers for Disease Control and Prevention: Tickborne diseases of the United States. A Reference Manual for HealthCare Providers. 6th ed. 2022. Accessed September 21, 2022. Available at

Method Name


Specimen Type


Specimen Required

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions: Centrifuge and aliquot serum into plastic vial.

Specimen Minimum Volume

0.2 mL

Specimen Stability Information

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

Reference Values

IgG: <1:64

IgM: <1:64

Reference values apply to all ages.

Test Classification

This test has been cleared, approved, or is exempt by the US 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

Test ID Test Order Name Order LOINC Value
SFGP Spotted Fever Group Ab, IgG, IgM, S 90260-1


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

For more information see Acute Tick-Borne Disease Testing Algorithm.


If not ordering electronically, complete, print, and send Infectious Disease Serology Test Request (T916) with the specimen.

Mayo Clinic Laboratories | Microbiology and Infectious Disease Catalog Additional Information: