Blood Tests

Reviewed by: HU Medical Review Board | Last updated: April 2021

There are several blood tests your doctor may use to diagnose and monitor rheumatoid arthritis (RA).

Certain substances may be present in the blood of people living with RA. They may also have high levels of common parts of blood that suggest inflammatory disease.1

Antinuclear antibody (ANA)

Antibodies are proteins the immune system makes to fight foreign substances like infections. In some cases, antibodies can also be harmful. When this happens, antibodies mistake healthy cells for harmful ones and attack them.

Many times, ANA levels are increased (positive) in RA. However, many people may have a positive ANA test and not have RA or another autoimmune disease. Results of the ANA test will help guide your doctor to your diagnosis.2,3

Rheumatoid factor (RF)

Rheumatoid factors (RF) are proteins made by your immune system that can attack healthy tissue.4

RF is a common RA blood test. Many people with RA have increased (positive) RF levels. This is often called seropositive RA. For some people with RA, rheumatoid factor may not show up in their blood test. This is known as seronegative RA.

RF testing continues to be an important part of diagnosing RA. The amount of rheumatoid factor in your blood may help your doctor decide your course of treatment.4

Complete blood count (CBC)

A complete blood count (CBC) is a common rheumatoid arthritis blood test. It measures various levels of cells and chemicals in your blood, including:5

  • Red blood cells (RBCs) – Carry oxygen in the blood
  • White blood cells (WBCs) – Help fight infection
  • Hemoglobin – Oxygen-carrying protein in the RBCs that gives blood its red color
  • Platelets – Help with blood clotting
  • Hematocrit – Percentage of RBCs in the blood

People with RA often have an abnormal CBC, with anemia decreased red blood cells or hemoglobin (anemia).6,7

Anti-citrullinated protein antibodies (ACPA)

Anti-citrullinated protein antibodies (ACPA) are harmful antibodies found in many people with RA. Like RF, ACPA may be found in early disease. This makes it an important diagnostic tool to get the RA treatment you need early on.8 This test is also known as anti-CCP, CCP antibody, and citrulline antibody.

What does a positive result mean?

Those who are ACPA-positive are more likely to have or develop RA. Some people who have ACPA in the blood will develop severe RA. Getting this test early in your disease journey may help your doctor decide on the best treatment you need for RA.8

Erythrocyte sedimentation rate (ESR)

Erythrocyte sedimentation rate (ESR) is a test that measures how quickly erythrocytes (red blood cells) fall through plasma (the colorless fluid part of the blood). This is known as a sedimentation rate.9

A faster-than-normal ESR is a sign of inflammation in the body. While an increased ESR could mean inflammation is related to RA, ESR is not a blood test that is specific only to RA. This means ESR is elevated in many different illnesses and diseases, not just in RA.9

C-reactive protein (CRP)

C-reactive protein (CRP) is a protein made in the liver. This level increases in response to inflammation.10,11

Why is CRP tested?

A common RA blood test, CRP is not as specific as ACPA or RF when diagnosing rheumatoid arthritis. CRP can be used to diagnose or monitor many different conditions, including:10,11

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