Rrickettsiigmcsfacnc

Published: August 9, 2026Updated: August 16, 2026

This test detects IgM antibodies against Rickettsia rickettsii (Rocky Mountain spotted fever bacteria) in cerebrospinal fluid to help diagnose infection affecting the central nervous system.

Quick summary

{"The test looks for IgM antibodies in cerebrospinal fluid (CSF) that your body produces in response to Rocky Mountain spotted fever infection","IgM antibodies typically appear early in infection, making this useful for detecting recent or acute cases","A positive result suggests the bacteria may have infected the central nervous system","The test requires a lumbar puncture (spinal tap) to collect CSF","Early diagnosis and treatment are critical as Rocky Mountain spotted fever can be life-threatening"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC: 18430-9
Short code: RICK-IgM-CSF
Synonyms: R rickettsi IgM CSF-aCnc
Category: cardiac
Sample: csf
Container: Sterile polypropylene tube for CSF collection (avoid glass tubes)
Units: N/A
Ref low: 0
Ref high: 1
Critical range: — – 64 N/A
Fasting: false
Population: adult
Sex: all
Age range: 0–120 years
Method: Immunofluorescence assay (IFA) or Enzyme-linked immunosorbent assay (ELISA) for detection of IgM antibodies against Rickettsia rickettsii
CPT: 86635
SNOMED: 128188006
Specimen volume: 1-2 mL CSF minimum; 2-3 mL preferred for adequate testing
Stability: CSF should be transported to laboratory immediately. Refrigerate at 2-8°C if delay <24 hours. Freeze at -70°C for long-term storage. Do not freeze at -20°C.
Hemolysis max: 200
TAT: 24–72 hours
Order: routine

What is this test?

This test checks for IgM (immunoglobulin M) antibodies against Rickettsia rickettsii bacteria in your cerebrospinal fluid (CSF). Rickettsia rickettsii is the germ that causes Rocky Mountain spotted fever, a potentially serious illness transmitted by tick bites. When your immune system detects this infection, it produces IgM antibodies as one of the first lines of defense. Finding these antibodies in CSF suggests the infection has spread to or is affecting your central nervous system (brain and spinal cord).

How is the sample collected?

Cerebrospinal fluid is collected through a procedure called a lumbar puncture, commonly known as a spinal tap. A healthcare provider inserts a thin needle into the lower back to withdraw a small amount of fluid from the space around the spinal cord. This sample is then sent to a laboratory for analysis.

What do the results mean?

A positive (reactive) result indicates that IgM antibodies against Rickettsia rickettsii were detected in your CSF. This typically means you have or recently had a Rocky Mountain spotted fever infection that may be affecting your central nervous system. A negative (non-reactive) result suggests no detectable IgM antibodies were found, but this does not completely rule out infection, especially if it is very early or late in the disease course. Your healthcare provider will interpret these results together with your symptoms, physical examination, and other test findings.

Reference range

Negative: < 1:64 titer or < 4 units (varies by laboratory method)N/A

Specimen: csf

Patient should be in lateral decubitus or sitting position for lumbar puncture. Inform patient of risks including post-lumbar puncture headache, bleeding, or infection. No fasting required.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

Why is this test done on CSF rather than blood?

Testing CSF directly is more specific for confirming that the infection has reached the central nervous system. While blood tests can detect antibodies systemically, finding them in CSF provides stronger evidence of neurological involvement, which is critical for guiding aggressive treatment and predicting complications.

Is a lumbar puncture painful?

You may feel some discomfort or pressure during the procedure, but it is generally well-tolerated. A local anesthetic is used to numb the area. Some people may experience a brief headache afterward, which can usually be managed with rest and fluids.

How soon after infection do IgM antibodies appear?

IgM antibodies typically develop within 7-10 days after infection with Rickettsia rickettsii. This test is most useful for detecting infections that are in the early to mid-stages. Your healthcare provider will consider the timing of your symptoms when interpreting results.

What happens if my test is positive?

A positive result confirms Rocky Mountain spotted fever with potential neurological involvement. Treatment with appropriate antibiotics (usually doxycycline) should begin immediately. Hospitalization may be required for severe cases. Early treatment significantly improves outcomes and reduces the risk of serious complications or death.

Can this test distinguish between current and past infection?

IgM antibodies generally indicate a more recent or current infection, as they tend to decline over time. However, the exact duration of IgM positivity can vary. Your healthcare provider may order additional tests (such as IgG antibody testing) or repeat testing to get a more complete picture of your infection status.

Sources

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 16, 2026. · Read our editorial policy