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Rrickettsiigmmsmtser

Published: August 9, 2026Updated: August 17, 2026

This blood test detects IgM antibodies against Rickettsia rickettsii, the bacterium that causes Rocky Mountain spotted fever, helping diagnose recent infection.

Quick summary

{"Detects early immune response to Rocky Mountain spotted fever","IgM antibodies appear within 7-10 days of infection","Often ordered with IgG test for comprehensive diagnosis","Early treatment is crucial to prevent serious complications","Results should be interpreted with clinical symptoms"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
110694-7
Short code
RICKIGM
Synonyms
R rickettsi IgM Msmt Ser
Category
cardiac
Sample
serum
Container
Serum separator tube (SST) or red top plain tube
Units
N/A
Ref low
0
Ref high
1
Critical range
— – 10000 N/A
Fasting
false
Population
adult
Sex
all
Age range
0–120 years
Method
Indirect Immunofluorescence Assay (IFA)
CPT
86757
SNOMED
122442009
Specimen volume
1.0-2.0 mL of serum
Stability
Room temperature: 24 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C or below): 30 days
Hemolysis max
50
Lipemia max
100
Icterus max
20
TAT
48–96 hours
Order
routine

What is this test?

The Rickettsia rickettsii IgM Antibody test is a blood test that detects IgM antibodies in your serum. IgM antibodies are the first type of antibodies your immune system produces when fighting a new infection. This test specifically looks for antibodies against Rickettsia rickettsii, the bacterium that causes Rocky Mountain spotted fever (RMSF), a potentially serious tick-borne disease.

Why is it ordered?

This test is typically ordered when you have symptoms suggestive of Rocky Mountain spotted fever, such as high fever, severe headache, rash (usually appearing 2-4 days after fever begins), muscle pain, and a history of tick bite or exposure to tick-infested areas. The test helps confirm whether your symptoms are due to RMSF so that appropriate treatment can begin promptly.

What do the results mean?

A positive IgM result indicates a recent or early infection with Rickettsia rickettsii. IgM antibodies typically appear within 7-10 days after infection and can persist for several months. A negative result does not completely rule out infection, especially if testing is done very early in the illness. Your healthcare provider may recommend repeat testing or additional tests (including IgG antibodies) to confirm the diagnosis.

What happens during the test?

A healthcare professional will draw a blood sample from a vein in your arm. The procedure is quick and generally causes minimal discomfort. The blood sample is then sent to a laboratory where it is analyzed for the presence of IgM antibodies against Rickettsia rickettsii.

Reference range

Negative: < 1:64 titer; Equivocal: 1:64 titer; Positive: >= 1:128 titerN/A

Specimen: serum

No special preparation required. Patient may eat and drink normally before sample collection.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

How long does it take to get results?
Results are typically available within 3-7 days, depending on the laboratory. Some specialized reference laboratories may take longer.
Do I need to fast before this test?
No fasting is required for this test. You can eat and drink normally before having your blood drawn.
Is the test painful?
You may feel a brief pinch or sting when the needle is inserted to draw blood. This is generally well-tolerated, and the discomfort subsides quickly.
Can this test distinguish between current and past infection?
IgM antibodies typically indicate recent or current infection, while IgG antibodies indicate past exposure or longer-standing infection. Often, both tests are ordered together to help determine the timing of infection.
What happens if my test is positive?
If your test is positive, your healthcare provider will likely start you on antibiotic treatment immediately, typically doxycycline, which is highly effective against Rocky Mountain spotted fever. Early treatment is essential for the best outcome.
  1. 1
    Centers for Disease Control and Prevention (CDC) - Rocky Mountain Spotted FeverSource
  2. 2
    May Clinic - Rocky Mountain Spotted FeverSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy