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Rheumatoid Factor (RF) - Results
About this test
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:
- A titer is a measure of how much the blood sample can be diluted before RF can no longer be detected. A titer of 1 to 20 (1:20) means that RF can be detected when 1 part of the blood sample is diluted by up to 20 parts of a salt solution (saline). A larger second number means there is more RF in the blood. So a titer of 1 to 80 shows more RF in the blood than a titer of 1 to 20.
- Nephelometry units show how much light is blocked by the blood sample in the tube. A high level of RF causes the sample to be cloudy, so less light passes through the tube than when the RF level is low. So an RF level of 100 units is higher than one of 40 units.
Normal
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.
| Titers | Less than 1:80 |
|---|---|
| Units | 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 values
High RF levels may be caused by:
- Rheumatoid arthritis. This is the most common reason for a positive rheumatoid factor (RF) level.
- Hepatitis C infection.
- Other autoimmune diseases, such as systemic lupus erythematosus (SLE), scleroderma, Sjögren's syndrome, and vasculitis.
- Infectious diseases, such as tuberculosis, mononucleosis, syphilis, and malaria.
- Liver diseases, such as cirrhosis and chronic active hepatitis.
- Infection of the heart (endocarditis).
- Leukemia.
| By: | Healthwise Staff | Last Revised: June 11, 2010 |
| Medical Review: | Kathleen Romito, MD - Family Medicine E. Gregory Thompson, MD - Internal Medicine | |
© 1995-2011 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated. This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.
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