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Rocky Mountain Spotted Fever (Blood)

Does this test have other names?

RMSF, Rocky Mountain spotted fever antibodies

What is this test?

Rocky Mountain spotted fever serum is a blood test used to look for antibodies, or proteins, that the body makes to fight Rocky Mountain spotted fever (RMSF) infections. RMSF is a serious bacterial infection caused by a bite from an infected tick. In most people, antibodies can't be found until at least a week after infection.

A blood sample is taken about a week after symptoms appear and again 2 to 4 weeks later. 

Why do I need this test?

You may need this test to confirm a diagnosis of RMSF and to see how well treatment is working. Symptoms of RMSF include:

  • Fever

  • Rash. This can happen 2 to 5 days after the fever, but some people never have a rash.

  • Headache

  • Muscle pain

  • Nausea

  • Vomiting

  • Belly (abdominal) pain

What other tests might I have along with this test?

Your healthcare provider might order other blood tests. These might include a complete blood cell count (CBC) and a chemistry panel. A low platelet count, low sodium level, or higher liver enzymes could mean RMSF. If you have a skin rash, your provider may order a skin biopsy to look for bacterial infection in the cells that line your blood vessels. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

If your first test results are negative, it's still possible you are infected. It's critical to start treatment right away, so your healthcare provider may suggest treatment even if your results are negative. He or she will have you repeat the test in a week or two.

Healthcare providers look for a rise in the antibodies. If the second test shows a significant rise in antibodies, it can confirm that you have RMSF.

The antibodies may stay at higher levels for months or even years after infection. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Antigens may be present in your blood if you have been exposed to related organisms. Antibiotic treatment also can affect your test results.

How do I get ready for this test?

You don't need to prepare for this test. 

Medical Reviewers:

  • Turley, Ray, BSN, MSN
  • Ziegler, Olivia Walton, MS, PA-C