Rickettsia (RMSF) Antibodies, (IgG/IgM) with Reflex to Titers

Rickettsia antibody, Rocky Mountain Spotted Fever Antibodies, IgG/IgM

Test Codes

EPIC: LAB1231921, Beaker: RMSFIGGIGM, Quest: 6419

Department

Send Outs

Specimen Collection Criteria

Collect: One Gold-top SST tube.
Also Acceptable: One Red-Top tube.

Physician Office/Draw Specimen Preparation

Let specimen clot 30-60 minutes then centrifuge to separate serum from cells. Transfer serum to a plastic transport tube and keep at room temperature (20-26°C or 68-78.8°F).

Preparation for Courier Transport

Transport: 1.0 mL serum, room temperature (20-26°C or 68-78.8°F). (Minimum: 0.2 mL)

Rejection Criteria

• Gross hemolysis.
• Grossly lipemic.
• Specimens not collected and processed as indicated.

In-Lab Processing

Let specimen clot 30-60 minutes then centrifuge to separate serum from cells. Transfer serum to a plastic transport tube keep at room temperature (20-26°C or 68-78.8°F)

Transport: 1.0 mL serum, room temperature (20-26°C or 68-78.8°F). (Minimum: 0.2 mL)

Storage

Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 7 days
Refrigerated (2-8°C or 36-46°F): 14 days
Frozen (-20°C/-4°F or below): 3 days

Specimen Storage in Department Prior to Disposal:

Specimen retention time is determined by the policy of the reference laboratory. Contact the Send Outs Laboratory with any questions.

Laboratory

Sent to Quest Diagnostics, Wood Dale, IL.

Performed

Tuesday, Friday.
Results available in 3 days.

Reference Range

                        Screen               Titer
RMSF (IgG)    Not detected    <1:64
RMSF (IgM)   Not detected    <1:64

Test Methodology

Immunofluorescence Assay (IFA).

Interpretation

• These tests are for antibodies to Rickettsia rickettsii. Any antibody reactivity to Rickettsia rickettsii should, however, also be considered group reactive for the Spotted Fever group (Rickettsia conorii, Rickettsia australis, and Rickettsia sibirica). A low positive suggests past exposure or infection, while high positive results may indicate recent infection, but are inconclusive for diagnosis. Seroconversion between acute and convalescent sera is considered strong evidence of recent infection. The best evidence for infection is a significant change on two appropriately timed specimens where both tests are done in the same laboratory at the same time.
• While the presence of IgM antibodies suggests recent infection, low levels of IgM antibodies may occasionally persist for more than 12 months post infection.
• Analyte Specific Reagents (ASRs) are used in many laboratory tests necessary for standard medical care and generally do not require FDA approval. This test was developed, and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the U.S. Food and Drug Administration.
• Rocky Mountain Spotted Fever, IgM is screened by ELISA and confirmed by IFA if indicated.

Clinical Utility

Rickettsia (RMSF) Antibodies (IgG, IgM) with Reflex to Titers - Antigen specific IgG and IgM titers allow rapid diagnosis of infection by any of the spotted fever group of rickettsial agents. This group of agents include R. rickettsii (Rocky Mountain Spotted Fever) and R. akari (rickettsial pox), both seen in the continental United States.

Clinical Disease

• Rocky Mountain spotted fever (RMSF) is a systemic, febrile illness with a characteristic rash usually occurring before the sixth day of illness. Fever, headache, myalgia, toxicity, confusion, nausea, vomiting, and anorexia are major clinical features. Abdominal pain, diarrhea, and cough are noted less frequently. The rash initially is erythematous and macular, and later can become maculopapular and frequently petechial. Rash first appears on the wrists and ankles, spreading within hours proximally to the trunk. The palms and soles typically are involved. Although early development of a rash is a useful diagnostic sign, in some cases the rash fails to develop or only does so late in the illness.
• Thrombocytopenia of varying severity develops in most cases, and anemia has been noted in approximately 30% of patients as a result of endothelial and microvascular damage. Leukopenia is noted less frequently. The illness can last as long as 3 weeks and can be severe with prominent central nervous system disease; involvement of cardiac, pulmonary, gastrointestinal tract, renal, and /or other organs; disseminated intravascular coagulation; and shock leading to death. Significant long-term sequelae, particularly neurologic, are common in patients with severe RMSF. (1)

Epidemiology

• Persons with occupational or recreational exposure to the tick vector (e.g., pet owners, animal handlers, and out-door persons) are at an increased risk of acquiring the organism. Persons of all ages, races, socioeconomic status, and both sexes can be infected, but most cases occur in those younger than 15 years, probably because they are most frequently in tick habitats. Mortality is highest in males, in persons older than 30 years, in nonwhites, and in persons with no known tick bite or attachment. Delay in disease recognition and resulting late initiation of appropriate antimicrobial therapy increases the risk of death. (1)
• The disease is widespread in the United States. Most cases are reported in the south Atlantic, southeastern, and south-central states. April through October are the months of highest prevalence. (1)

Incubation Period

Usually about 1 week, but ranges from 2 to 14 days. It appears to be related to the size of the rickettsial inoculum. (1)

Transmission

RMSF is transmitted to humans by the bite of ticks. (1)

Reference

1. American Academy of Pediatrics. Rocky Mountain Spotted Fever. In: Peter G, ed. (1997) Red Book: Report of the Committee on Infectious Diseases. 24th ed. Elk Grove Village, IL: American Academy of Pediatrics; 1997:452-454.

CPT Codes

86757 x2.

Contacts

Last Updated

11/19/2025