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Rickettsia rickettsii (Rocky Mountain Spotted Fever) Antibody, IgM
0050372
Ordering Recommendation

Detects antibodies during acute phase; paired concurrent specimen with IgG reduces false positive rate. Convalescent sera may be required for diagnosis.

Mnemonic
RMSF M
Methodology
Semi-Quantitative Indirect Fluorescent Antibody
Performed
Mon-Fri
Reported
1-4 days
New York DOH Approval Status
This test is New York DOH approved.
Submit With Order
ARUP Consult®
Disease Topics
Specimen Required
Patient Preparation
 
Collect
Serum Separator Tube (SST). 
Specimen Preparation
Separate serum from cells ASAP or within 2 hours of collection. Transfer 1 mL serum to an ARUP Standard Transport Tube. (Min: 0.1 mL) Parallel testing is preferred and convalescent specimens must be received within 30 days from receipt of the acute specimens. 
Storage/Transport Temperature
Refrigerated. 
Unacceptable Conditions
Contaminated, hemolyzed, or severely lipemic specimens. 
Remarks
Mark specimens plainly as "acute" or "convalescent." 
Stability
After separation from cells: Ambient: 48 hours; Refrigerated: 2 weeks; Frozen: 1 year (avoid repeated freeze/thaw cycles) 
Reference Interval
Less than 1:64Negative - No significant level of IgM antibody detected.
1:64 or greaterPositive - 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.

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.

Components
Component Test Code*Component Chart NameLOINC
0050372Rocky Mt Spotted Fever IgM5308-2
* 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.
Aliases
  • Rickettsia
  • RMSF
  • Rocky Mountain Spotted Fever