There are numerous blood tests for rheumatoid arthritis that can assist with diagnosis. The blood tests a doctor orders can depend on a person’s symptoms and the outcome of the physical examination.

Doctors can test blood samples for several inflammatory and immune system markers that are usually present in a person who has RA.

This article discusses the types of blood tests that can help determine whether or not a person has RA. It also discusses other methods of diagnosing the condition.

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The following are some blood tests that a doctor may order if they think that a person could have RA. Usually, the doctor draws several blood samples from one vein to conduct the different tests.

The doctor might not order all of the tests below. The tests they choose will depend on the person’s symptoms and the outcome of the physical examination.

What are 12 early signs of RA? Find out here.

Anti-cyclic citrullinated peptide

This test looks for a specific auto-antibody called anti-cyclic citrullinated peptide (anti-CCP). About 75% of people with RA will have anti-CCP.

If a person has RA and anti-CCP antibodies, they have seropositive RA. People with seronegative RA have RA, but they do not have anti-CCP antibodies.

To interpret the results, the doctor will look at them alongside those of a rheumatoid factor (RF) test, which this article describes in detail later on. The doctor will likely assess the results as follows:

positive CCP antibodies and positive RFThe person likely has RA.
positive CCP antibodies and negative RFThe person has early stage RA or is likely to develop it.
negative CCP antibodies and negative RFThe person has a lower chance of developing RA.

The normal range of anti-CCP is 0–20 units per milliliter (ml). If a person has more than this, they may have RA.

Learn more about seronegative and seropositive RA here.

Rheumatoid factor

This test measures the level of RF, which acts as an antibody against gamma globulins, which are a type of normal protein in the blood.

The normal RF range is 0–20 units per ml. Having a higher level than this might point to RA, but this alone does not confirm the presence of the condition. Several other health conditions can increase levels of RF in the body, and around 5% of people with high RF levels do not have RA.

Similarly, around 20% of people who have RA do not have high levels of RF. This is why doctors may need other tests, such as the anti-CCP test, to confirm a diagnosis.

In some cases, certain viruses can trigger symptoms similar to those of RA and lead to a positive RF test result. Examples of viruses that can cause this include parvovirus B19 and hepatitis C.

A person may need to have additional tests, such as a hepatitis C antibody test, to exclude these viral infections. That said, a doctor may only need to test for viruses such as parvovirus if there is a proven risk of exposure — for example, if a person has come into contact with an at-risk group, such as children.

Learn more about the RF test and its results here.

Antinuclear antibody

This test looks for high levels of antinuclear antibodies (ANAs). These are blood proteins that can attack a cell’s nucleus, destroying the cell.

ANAs can be present in people with a number of conditions, including RA, scleroderma, Sjögren’s, and mixed connective tissue disease. For this reason, a positive result on an ANA test alone cannot confirm that RA is present.

Learn more about the ANA test here.

C-reactive protein

This test checks for the presence of C-reactive protein (CRP), which the liver produces in response to inflammation in the body. The protein helps regulate immune reactions, and the results of a CRP test can indicate systemic inflammation.

The presence of CRP can indicate inflammation anywhere in the body, and a positive test result may indicate RA or another condition, such as diabetes, obesity, metabolic syndrome, heart disease, depression, or lung disease.

Most laboratories consider the normal CRP range to be below 1 milligram (mg) per liter.

Learn more about the link between RA and CRP here.

Erythrocyte sedimentation rate

This test measures the speed at which the red blood cells in a blood sample clump together and settle at the bottom of a test tube over an hour. Doctors also sometimes call this the sed rate. It can indicate whether or not there is inflammation in the body.

Other factors besides RA, such as infection and older age, can lead to a high erythrocyte sedimentation rate (ESR). A person’s results can also vary over time.

For males, normal ESR rates range from 0–20 millimeters (mm) per hour, depending on their age. For females, the normal range is 0–30 mm per hour, depending on their age. These ranges tend to be higher in people older than 50 years.

Learn more about the ESR test and its results here.

Human leukocyte antigen tissue typing

This test checks for a genetic marker called human leukocyte antigen (HLA).

Some studies suggest that around 60% of RA cases may be inherited. If a person has specific antigens, it could mean that they have a higher likelihood of developing RA. However, other factors, such as tobacco use, can also trigger the condition.

HLA markers in the blood can help indicate the likelihood of developing an immune-related condition such as RA. These markers may also be a sign of another condition, such as ankylosing spondylitis or reactive arthritis.

Lyme serology

Doctors use certain tests to rule out other conditions that cause symptoms similar to those of RA. This test detects the presence of antibodies that indicate Lyme disease.

If a person has Lyme serology immune factors, it may mean that they have Lyme disease rather than RA.

Uric acid

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.

A person typically has a high level of uric acid, also known as hyperuricemia, when their blood levels are higher than 800 mg per day in men and 750 mg per day in women. When this happens, the person is more likely to have gout than RA.

Learn more about uric acid tests here.

Complete blood count

The complete blood count (CBC) test checks the blood’s white blood cells, which are responsible for fighting infections and clotting the blood, and red blood cells, which take oxygen to all the organs in the body using the protein hemoglobin.

Doing a CBC test can be useful for people with RA because they tend to be anemic. This means that they may not have enough healthy blood cells.

If a person’s hemoglobin level is under 12 grams (g) per deciliter (dl) in females or under 13 g per dl in males, doctors will classify them as anemic. RA may be a potential cause.

Complete metabolic panel

This test checks the function of the liver and the kidneys. It looks at the blood levels of sodium, potassium, chloride, glucose, creatinine (which specifically measures kidney function), and aspartate transaminase and alanine transaminase (which specifically measure liver function).

Certain medications to treat RA can impact the liver and the kidneys. Based on the results of the test, a doctor may adjust a person’s medications.

Beyond blood tests, the following factors can help doctors make an RA diagnosis:

  • the presence of RA symptoms, 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

Receiving a prompt diagnosis is key. Getting early treatment can help slow the progression of the condition.

Results of a combination of blood tests can help doctors diagnose or rule out RA. Doctors also use imaging studies and physical examinations to help determine the cause of a person’s symptoms.

Before having a blood test, a person should check whether or not any preparation, such as fasting, is necessary.

Read this article in Spanish.