What is rheumatoid factor?
Rheumatoid factor is an antibody that can bind itself to other antibodies within the body. Antibodies are normal proteins that are in our blood stream and are an important part our immune system. However rheumatoid factor is not normally found within the normal healthy individual, only 1-2% of healthy people. The measurable amount of rheumatoid factor usually increases with age with approximately 20% of people aged over 65.
What is the rheumatoid factor test used for?
A blood test is commonly used to detect the rheumatoid factor to aid the diagnosis of rheumatoid arthritis. Rheumatoid factor is usually detected in about 80% of adults also it can be detected in a smaller amount of children with juvenile rheumatoid arthritis.
Is it possible for rheumatoid factor to be found in somebody without rheumatoid arthritis?
Rheumatoid factor can be found in people who suffer from other conditions such as connective tissue diseases, hepatitis, parasites, tuberculosis, liver disease and sarcoidosis. It can also sometimes be found in healthy individuals though this is usually found when members of the family suffer from rheumatoid arthritis.
How is the test performed?
A blood sample is usually taken from the arm and then to a laboratory for analysis. This will also rule out or diagnose any other inflammation related issues that the individual could be suffering from.
Results From RF Test
There are two types of results that you could receive which are reported as titers or units.
A titer is a process whereby the blood test is diluted down until the rheumatoid factor is no longer detected.
A titer of 1 to 20 or (1:20) this means that RF can be detected when 1 part blood is diluted upto 20 parts of saline. If say for instance that the second number was 60 it would show that there is more RF in the blood than a titer of 1 to 20.
Units or nephelometry units show how much light is being blocked by the blood sample in the tube. A relatively high level of RF would cause the blood sample to look cloudy and therefore less light would be able to pass through the tube. For example an RF level of 100 units is a lot higher than a sample showing only 40 units.
The normal values displayed below are a reference range and are shown just as a guide. Results obtained from various labs can differ in ranges for what is normal. When you receive your results your doctor will evaluate these based on other factors and your health. What this means that if a value falls outside the normal range it may still be normal for you.
Titers: Less than 1:80
Units: Less than 60 units per millilitre (U/mL)
A health professional will always use the results of an Rheumatoid Factor test along with information gained from a medical history and physical examination before diagnosing rheumatoid arthritis.