Diagnosing Rheumatoid Arthritis
There’s no single test for rheumatoid arthritis (RA). To
help diagnose and treat the condition, your doctor will ask about your:
- medical history
- risk factors
Your doctor will also perform a physical exam and run
one or more tests.
In 2010, the American College of Rheumatology
(ACR) updated the diagnostic criteria for RA. Currently, a positive diagnosis
requires at least six points on a classification scale. In order to get six
points, a person must have:
- symptoms affecting one or more joints (up to
- positive test results on a blood test for
either rheumatoid factor (RF) or anti-citrullinated protein antibody
(ACPA) (up to three points)
- positive c-reactive protein or erythrocyte
sedimentation tests (one point)
- symptoms lasting longer than six weeks (one
At least one blood test must be
positive to confirm the diagnosis.
Some doctors also use a more
symptom-based criteria to diagnose RA.
Blood Tests for Rheumatoid Arthritis
RA is an autoimmune disease. Several different blood
tests can detect immune system changes associated with RA. Some detect
antibodies that may attack the joints and other organs. Others measure
inflammation or overall immune system function.
Rheumatoid Factor Test
According to the ACR, RF is an antibody found in the
blood of most people with RA. Higher levels of RF correlate with more severe
symptoms and faster progression. However, RF tests alone cannot be used to
diagnose RA. Some people with RA test negative for RF. Other people without RA
may test positive.
Anti-Citrullinated Protein Antibody Test
According to Mayo Clinic, anti-cyclic citrullinated peptide
(ACPA or anti-CCP) is another antibody associated with RA. If you test positive
for ACPA, there’s good chance you have rheumatoid arthritis. A positive test
also indicates that RA is likely to progress more quickly.
People without RA almost never test positive for ACPA.
However, many RA patients test negative for ACPA. Therefore, this test is
usually used in combination with other tests.
Anti-Nuclear Antibody Test
Anti-nuclear antibody (ANA) tests are a general
indicator of autoimmune disease. Many people with RA have positive ANA tests.
However, a positive test does not mean you have RA. Many people have positive
ANA tests with no noticeable disease.
Erythrocyte Sedimentation Rate
Also called sed
rate or ESR,
this test measures how quickly red blood cells separate out of the blood. The
sed rate is a measure of inflammation. There is typically a direct correlation
between the level of the sed rate and the degree of inflammation.
C-Reactive Protein Test
C-reactive protein is produced in the liver when there
is severe inflammation or infection in the body. C-reactive protein levels
change more quickly than sed rates. Therefore, this test is sometimes used to
measure the effectiveness of RA medications. It can also contribute to a
diagnosis of RA.
Other Tests for Rheumatoid Arthritis
In addition to blood tests for RA, other tests can also
be used to detect damage caused by the disease.
X-rays can be used to take images of joints affected by
RA. These pictures can assess the level of damage to:
This can help determine the best method of treatment.
A series of X-rays can be taken over a period of weeks
or months to monitor RA progression. However, X-rays are not helpful in
detecting the presence of early RA because the early soft tissue inflammation does not
show up on X-ray images. They can only be used to detect more
Magnetic Resonance Imaging (MRI)
MRIs use a powerful magnetic field to take a picture of
the inside of the body. Unlike X-rays, MRIs can create images of soft tissues.
Therefore, they can be used to look for inflammation of the synovium. The
synovium is the membrane surrounding the joints. It’s what the immune system
attacks during RA.
MRIs can detect inflammation due to RA far earlier than
an X-ray. However, they are not widely used in diagnosis.