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A rheumatoid factor (RF) blood test measures the amount of the RF antibody present in the blood. Normally, antibodies are produced by the immune system to help destroy and eliminate invading bacteria and viruses that can cause disease. But the RF antibody can attach to normal body tissue, resulting in damage.
A high level of rheumatoid factor can be caused by several autoimmune diseases (including rheumatoid arthritis) and some infections. Occasionally an elevated level of RF is present in healthy people.
The amount of rheumatoid factor in blood can be measured in two ways:
A test for rheumatoid factor is done to help support a diagnosis of rheumatoid arthritis.
This test is also done to find out whether a child who has polyarticular juvenile idiopathic arthritis has elevated rheumatoid factor. This can help determine the likely progression of the disease, and the best treatment for it.
You do not need to do anything before you have this test.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).
The health professional drawing blood will:
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from having a blood sample taken from a vein.
A rheumatoid factor (RF) blood test measures the amount of the RF antibody present in the blood.
The results of the rheumatoid factor (RF) test may be reported in titers or units:
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
You can usually get the results within 24 hours.
Less than 1:80
Less than 60 units per milliliter (U/mL)
Check with your doctor to see what the normal range is for the lab that tested your blood.
High RF levels may be caused by:
Reasons you may not be able to have the test or why the results may not be helpful include:
CitationsPagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.Other Works ConsultedFischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Current as of: June 4, 2012
Author: Healthwise Staff
Medical Review: Anne C. Poinier, MD - Internal Medicine & Kathleen Romito, MD - Family Medicine
To learn more, visit Healthwise.org
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