Ordering Recommendation

Preferred test for acute or convalescent phase of disease. Acute and convalescent titers often necessary.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Serum Separator Tube (SST).

Specimen Preparation

Separate from cells ASAP or within 2 hours of collection. Transfer 1 mL serum to an ARUP standard transport tube. (Min: 0.4 mL) Parallel testing is preferred and convalescent specimens must be received within 30 days from receipt of the acute specimens.

Storage/Transport Temperature


Unacceptable Conditions

Contaminated, hemolyzed, or severely lipemic specimens.


Mark specimens plainly as "acute" or "convalescent."


After separation from cells: Ambient: 48 hours; Refrigerated: 2 weeks; Frozen: 1 year (avoid repeated freeze/thaw cycles)


Semi-Quantitative Indirect Fluorescent Antibody (IFA)




1-3 days

Reference Interval

Test Number
Reference Interval
  Rocky Mt Spotted Fever IgG Less than 1:64
  Rocky Mt Spotted Fever IgM Less than 1:64

Interpretive Data

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.

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.

Seroconversion, a fourfold or greater rise in antibody titer, between acute and convalescent sera is considered strong evidence of recent infection. Acute-phase specimens are collected during the first week of illness and convalescent-phase samples are generally obtained 2-4 weeks after resolution of illness. Ideally these samples should be tested simultaneously at the same facility. If the sample submitted was collected during the acute-phase of illness, submit a marked convalescent sample within 25 days for paired testing.

Unit Of Measure
Rocky Mt Spotted Fever IgG Less than 1:64
1:64 - 1:128    
1:256 or greater
Negative - No significant level of IgG antibody detected.
Low Positive - Presence of IgG antibody detected, suggestive of current or past infection.
Positive - Presence of IgG antibody suggestive of recent or current infection.
Rocky Mt Spotted Fever IgM Less than 1:64
1:64 or greater
Negative - No significant level of IgM antibody detected.
Positive - Presence of IgM antibody detected, which may indicate a current or recent infection; however, low levels of IgM antibodies may occasionally persist for more than 12 months post-infection.

Compliance Category



Hotline History


CPT Codes

86757 x2


Component Test Code* Component Chart Name LOINC
0050369 Rocky Mt Spotted Fever IgG 5307-4
0050372 Rocky Mt Spotted Fever IgM 5308-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • Rickettsia
  • RMSF
  • Rocky Mountain Spotted Fever
Rickettsia rickettsii (Rocky Mountain Spotted Fever) Antibodies, IgG & IgM by IFA