Rheumatoid Factor (RF)
How It Feels
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
There is very little chance of a
problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You
can lower the chance of bruising by keeping pressure on the site for several
- In rare cases, the vein may become swollen after the
blood sample is taken. This problem is called phlebitis. A warm compress can be
used several times a day to treat this.
- Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.
A rheumatoid factor (RF) blood test
measures the amount of the RF
antibody present in the blood.
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
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.
Check with your doctor to see what the normal range is
for the lab that tested your blood.
High RF levels may be caused