Rheumatoid arthritis is an autoimmune disorder that causes inflammation in the joints. A doctor will diagnose rheumatoid arthritis by asking a person about their symptoms, carrying out a physical examination, taking blood tests, and using imaging studies.
Doctors may test blood samples for several inflammatory and immune system compounds that are usually present in a person who has rheumatoid arthritis (RA).
In this article, learn more about these blood tests and other diagnostic methods for RA.
The following are some of the blood tests that a doctor may order to help diagnose RA.
Usually, a medical professional can draw several blood samples from one vein to conduct different tests.
Drawing several blood samples at once avoids the need for using multiple needles.
A doctor might not order all of the tests below to diagnose RA.
The tests that they choose will depend on the person's symptoms and the outcome of the physical examination.
1. Anti-cyclic citrullinated peptide (anti-CCP)
What it tests: This test looks for a specific auto-antibody called anti-CCP, which is present in an estimated 60 to 80 percent of people with RA, according to the Arthritis Foundation.
Interpreting the results: If a person has anti-CCP levels higher than 20 units per milliliter (u/ml), they may have an increased risk of RA.
The anti-CCP test is similar to the rheumatoid factor antibody test, which features later on in this article. However, doctors often use it in preference to the rheumatoid factor test for greater accuracy.
2. Antinuclear antibody (ANA)
What it tests: This test looks for high levels of antinuclear antibodies, which are compounds that can attack a cell's nucleus, destroying the cell.
Interpreting the results: Doctors use this test to check for several different conditions, including RA, scleroderma, Sjogren's syndrome, and mixed connective tissue disease.
3. C-reactive protein (CRP)
What it tests: This tests detects the presence of CRP, which the liver produces in response to inflammation in the body.
Interpreting the results: The presence of CRP can indicate inflammation anywhere in the body, but certain medical conditions, such as obesity and infection, can also increase CRP in the blood.
4. Erythrocyte sedimentation rate (ESR)
What it tests: This test lasts for 1 hour, and it measures the speed at which the red blood cells in a sample of blood settle at the bottom of a test tube.
Interpreting the results: Elevated ESR results can indicate inflammation in the body. However, some other conditions, such as anemia and infection, can also cause an elevated ESR.
A person's ESR levels tend to increase as they age, so their results will vary over time.
5. HLA tissue typing
What it tests: This test detects the presence of a genetic marker called HLA-B27 in the blood.
People with these conditions will almost always have HLA-B27 markers in their blood.
6. Lyme serology
What it tests: As with the uric acid test below, doctors use this test to rule out other conditions that are similar to RA. This test detects the presence of antibodies that indicate Lyme disease.
Interpreting the results: The presence of Lyme serology immune factors may signify that a person has Lyme disease rather than RA.
7. Rheumatoid factor (RF)
What it tests: This test measures the level of RF, which acts as an antibody against gamma globulins in the blood.
Interpreting the results: A person who tests positive for RF could have RA. However, doctors cannot conclude this from an RF test alone as several other conditions can increase the amount of RF in the body, including gout.
Similarly, a negative RF test result is insufficient evidence to confirm that a person does not have RA.
The presence of RF alongside anti-CCP and symptoms typical of RA, however, make it likely that a person has this condition.
8. Uric acid
What it tests: Uric acid is a waste product that tends to be present in high amounts when a person has gout, which is another form of inflammatory arthritis.
Interpreting results: The presence of high levels of uric acid indicate that a person is more likely to have gout than RA.
In addition to blood tests, a doctor will consider the following when making an RA diagnosis:
- symptoms relevant to RA, such as swelling and pain in the hands, wrists, and knees
- imaging studies that suggest damage to the joints or reveal fluid-filled areas around them
- joint fluid samples that look for uric acid crystals or other compounds
The correct diagnosis is vital to managing RA. Early treatment can help slow down the progression of the disease.
Blood test results can help doctors diagnose RA or rule out the condition as being the underlying cause of a person's symptoms.
In addition to blood tests, doctors are likely to use imaging studies and a physical examination to help determine what is causing the individual's joint pain.
Before having a blood test, it is best to check with a doctor if it is necessary to prepare for it in any way, such as by not eating for several hours beforehand.