Rheumatoid Factor (RF)
A rheumatoid factor (RF) blood test measures the amount of the RF Reference antibody Opens New Window 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.
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 Reference units per milliliter Opens New Window (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:
- Reference Rheumatoid arthritis Opens New Window.
- Other autoimmune diseases, such as Reference systemic lupus erythematosus (SLE) Opens New Window, Reference scleroderma Opens New Window, Reference Sjögren's syndrome Opens New Window, and vasculitis.
- Infectious diseases, such as Reference tuberculosis Opens New Window, Reference mononucleosis Opens New Window, Reference syphilis Opens New Window, and Reference malaria Opens New Window.
- Liver diseases, such as Reference cirrhosis Opens New Window and Reference hepatitis Opens New Window.
- Infection of the heart (Reference endocarditis Opens New Window).
- Reference Leukemia Opens New Window.
|By:||Reference Healthwise Staff||Last Revised: Reference June 4, 2012|
|Medical Review:||Reference Anne C. Poinier, MD - Internal Medicine
Reference Kathleen Romito, MD - Family Medicine