How Rheumatoid Arthritis Is Diagnosed

How the Disease and Disease Remission Are Confirmed

Doctor examining patient's hand
Hero Images/Getty Images

Rheumatoid arthritis differs from osteoarthritis ("wear-and-tear" arthritis) in that it is an autoimmune disorder in which the immune system mistakenly attacks its own cells and tissues, primarily those of the joints. As such, the disease cannot diagnose by symptoms alone. Instead, you need to use a combination of tests—including a physical exam, imaging tests, and blood tests—to determine whether the results meet the clinical definition of the disease.

Doing so not only ensures that the diagnosis is correct, it helps determine the appropriate course of treatment.

Physical Exam

One of the first tools of diagnosis is a physical exam. The aim of the evaluation is, in part, to determine the characteristics of the joint pain and swelling to better distinguish it from the most likely suspect, osteoarthritis.

Among the key differences:

  • Rheumatoid arthritis tends to affect multiple joints (polyarthritis). Osteoarthritis usually affects the hands, feet, and knees and oftentimes involves a single joint (monoarthritis).
  • Rheumatoid arthritis tends to be symmetrical, meaning that joint symptoms on one side of the body will often be mirrored on the other side of the body. Osteoarthritis is more often unilateral (or asymmetrical if more than one joint is involved).
  • Because rheumatoid arthritis causes systemic (whole-body) inflammation, fatigue, malaise, and even a low-grade fever are common. Osteoarthritis, which is not an inflammatory disease, will usually not be accompanied by these symptoms.
  • Morning stiffness is common with rheumatoid arthritis but tends to last only 30 minutes and improve with gentle movement. Since osteoarthritis involves permanent structural joint damage, the morning stiffness will generally last much longer.

In addition to evaluating your physical symptoms, the doctor will review your family history.

Rheumatoid arthritis can often run in families, doubling your risk of the disease if a second-degree relative has it and tripling your risk if an immediate family member is affected.

Lab Tests

Lab tests are used for two primary purposes in diagnosing rheumatoid arthritis: to classify your serostatus and to measure and monitor the level of inflammation in your body.

Serostatus

Serostatus (loosely translated as "blood status") refers to the key identifiers of the disease in your blood. If these compounds are detected in a blood test, you are said to be seropositive. If they are not found, you would be classified as seronegative. Seropositive results can be classified as either low positive, moderate positive, or high/strong positive.

There are two tests used to establish your serostatus:

  • Rheumatoid factor (RF) is a type of autoantibody found in 80 percent of people living with the disease. Autoantibodies are proteins produced by the body that attack healthy cells. While high levels of RF are strongly suggestive of rheumatoid arthritis, they can occur with other autoimmune diseases such as lupus or non-autoimmune disorders such as cancer and chronic infections.
  • Anti-cyclic citrullinated peptide (anti-CCP) is another type of autoantibody found in the vast majority of people with rheumatoid arthritis. The high specificity of the test—its ability to correctly identify anti-CCP—is such it can often identify family members at risk of the disease even if they haven't any symptoms.

    Where both tests fall short is in their sensitivity, which is generally below 80 percent. What this means is that the tests, while valuable in making a diagnosis, are prone to ambiguous or false-negative results. It is for this reason that they are used as part of the diagnostic process rather than as sole indicators.

    Inflammatory Markers

    Inflammation is the defining characteristic of rheumatoid arthritis. Testing is done to evaluate the level of inflammation by looking at key markers in the blood. These markers not only help us confirm the initial diagnosis but are used throughout the course of the disease to assess our response to treatment.

    To this end, doctors will use two key measures:

    • Erythrocyte sedimentation rate (ESR) is a test that measures the rate by which red blood cells settle to the bottom of a long upright tube, known as a Westergren tube, in an hour. If there is inflammation, the red blood cells will stick together and sink more quickly. It is a non-specific measurement of inflammation but one that can provide key insights valuable to a diagnosis.
    • C-reactive protein (CRP) is a type of protein produced by the liver in response to inflammation. While also non-specific, is a more direct measure of the inflammatory response.

    ESR and CRP can also be used to diagnose arthritis remission, the state of low disease activity where inflammation is more or less in check.

    Imaging Tests

    The role of imaging tests in rheumatoid arthritis is to identify the signs of joint damage, include bone and cartilage erosion and the narrowing of the joint spaces. They can also help track the progression of the disease and establish when surgery is needed.

    Each test can provide different and specific insights:

    • X-rays are especially useful in identifying bone erosion and joint damage. While X-rays are considered the primary imaging tool for arthritis, they are not as helpful in the very early stages of the disease when changes in cartilage and synovial tissues are less apparent.
    • Magnetic resonance imaging (MRI) scans are able to look beyond the bone and spot changes in connective tissue and even positively identify joint inflammation in early disease.
    • Ultrasounds are also better at spotting early joint erosion and can reveal specific areas of joint inflammation. This is a valuable feature given that inflammation can sometimes continue invisibly even though the ESR and CRP tell us that the person is in remission. In such case, treatment would be continued until such time as a true remission is achieved.

    Classification Criteria

    In 2010, the American College of Rheumatology (ACR) updated its longstanding classification criteria for rheumatoid arthritis. The revisions were motivated, in part, by advances in diagnostic technologies. While the classifications are intended for clinical research purposes, they are nevertheless used in clinical practice to provide a greater degree of diagnostic certainty.

    The 2010 ACR/EULAR Classification Criteria looks at four different clinical measures and rates them on a scale of 0 to 5. A cumulative score of 6 to 10 can provide a high degree of confidence that you, in fact, have rheumatoid arthritis.

    CriteriaValuePoints
    Duration of symptomsLess than six weeks0
     More than six weeks1
    Joint involvementOne large joint0
     Two to 10 large joints1
     One to three small joints (without the involvement of larger joints)2
     Four to 10 small joints (without the involvement of larger joints)3
     Over 10 joints (with at least one small joint)5
    SerostatusRF and anti-CCP are negative0
     Low RF and low anti-CCP2
     High RF and high anti-CCP3
    Inflammatory markersNormal ESR and CRP0
     Abnormal ESR and CRP1

    Diagnosing Remission

    Diagnosing disease remission is not as straightforward a process. It requires not only diagnostic tests but a subjective assessment of what you, as the patient, feel about your condition. Accurately diagnosing remission is important because it determines whether certain treatments can be stopped or if doing so may be premature and cause a relapse.

    To this end, the ACR has established what is called the DAS28, which is comprised of four different measures. "DAS" is the acronym for "disease activity score," while 28 refers to the number of joints that are examined in the assessment.

    The DAS looks at the following:

    • The number of tender joints your doctor finds (out of 28)
    • The number of swollen joints your doctor finds (out of 28)
    • Your ESR and CRP results (normal versus abnormal)
    • How you feel your overall health is by marking your status on a 10-centimeter line in which one end is "very good" and the other is "very bad"

    These results are then fed into a complex mathematical formula to calculate your overall score. A DAS28 of greater than 5.1 implies active disease, less than 3.2 suggests low disease activity, and less than 2.6 is considered remission.

    Differential Diagnosis

    In the same way that tests can help differentiate between rheumatoid arthritis and osteoarthritis, others may be ordered to ascertain if there are other causes of your symptoms. This is especially true if your rheumatoid arthritis test results are either inconclusive, ambiguous, or negative.

    These may include autoimmune disorders, connective tissue diseases, and chronic inflammatory diseases such as:

    Sources:

    Aletaha, D.; Neogi, T.; Silman, A. et al. "2010 Rheumatoid Arthritis Classification Criteria: An American College of Rheumatology/European League Against Rheumatism Collaborative Initiative." Arthritis Rheum. 2010: 62(9): 2565-81 DOI: 10.1002/art.27584.

    Anderson, J.; Caplan, L.; Yazdany, J. et al. "Rheumatoid Arthritis Disease Activity Measures: American College of Rheumatology Recommendations for Use in Clinical Practice." Arthritis Care Res. 2012; 64(5):6. DOI: 10.1002/acr.21649.

    Bykerk, V. and Masarotti, E. "The new ACR/EULAR remission criteria: rationale for developing new criteria for remission." Rheumatology. 2012; 51:vi16vi20. DOI:10.1093/rheumatology/kes281.

    Smolen, J.; Aletaha, D.; and McInnes, I. “Rheumatoid arthritis.Lancet. 2017; 388(10055):2023-38. DOI: 10.1016/So140-6736(16)30173-8.