In rheumatoid arthritis (RA), joint inflammation is caused by the immune system mistakenly attacking the synovium, a membrane that lines and lubricates the inside of joints. There is no one test that is conclusive for a diagnosis of RA. RA is diagnosed through a combination of a physical examination, family history, blood tests, and imaging scans. In most cases, RA is diagnosed by a rheumatologist, or specialist in musculoskeletal and autoimmune diseases.
Rheumatoid arthritis — especially when the symptoms are mild — is often misdiagnosed. Joint pain in RA can resemble other chronic diseases including lupus, ankylosing spondylitis, psoriatic arthritis, Sjögren’s syndrome, gout, and osteoarthritis. A doctor carefully considers many different test results and which joint diseases they may indicate before concluding that RA is the correct diagnosis or ruling it out.
The American College of Rheumatology has established classification criteria for diagnosing RA. Criteria include an assessment of which joints (and how many) are involved, how long symptoms have been present, and results from certain blood tests. Based on these criteria, a rheumatologist may or may not diagnose "definite RA."
Typically, the rheumatologist will start by examining your joints to check for signs of disease activity, such as swelling, rheumatoid nodules, redness, warmth, and symmetry. In RA, symptoms are symmetrical, appearing on the same joints on both sides of the body. You may be asked about what times of day you experience symptoms — morning stiffness is common in RA. Mobility limitations and associated pain will also be assessed. You may also be asked about family medical history of RA or other autoimmune diseases. Having relatives with autoimmune conditions may increase your risk factors for developing RA.
Diagnosis may also involve blood tests or imaging procedures such as X-rays, ultrasound, or magnetic resonance imaging (MRI) scans. Scans allow the doctor to check for joint damage during diagnosis, and later measure how the disease progresses over time. Ultrasound and MRI were introduced more recently, and may aid in finding more subtle joint damage that can lead to an early diagnosis.
Although no lab test is conclusive for rheumatoid arthritis, each can provide important clues that make an RA diagnosis seem more likely or help rule it out.
Blood tests look for specific proteins that act as biomarkers for RA and other inflammatory conditions. One biomarker, anti-cyclic citrullinated peptide (anti-CCP), is found in around 60 percent to 70 percent of people with RA. Anti-CCPs can appear in blood years before RA symptoms appear. Bloodwork may also look for rheumatoid factor (RF), although RF can also be found in people with conditions other than RA. The presence of anti-CCP and RF indicate an autoimmune reaction.
Furthermore, if you go on to be diagnosed with RA, whether or not you test positive for RF or anti-CCP provides criteria for being typed as seropositive (having RF or anti-CCP in the blood) or seronegative (not having RF or anti-CCP in the blood). Knowing your type of RA helps your doctor better predict your disease course and recommend the medication most likely to be effective in managing your RA.
Blood tests can also check overall levels of inflammation by examining erythrocyte sedimentation rate (ESR or “sed rate”) and C-reactive protein (CRP). At elevated levels, both ESR and CRP are considered signs of inflammation and can indicate RA or another inflammatory condition.
Similarly, anemia, or low red blood cell count, is another lab result often seen in people with RA.
If a diagnosis of rheumatoid arthritis is confirmed, your doctor may recommend additional testing to check the health of your lungs and cardiovascular system. In addition to painful joints, inflammation in RA can lead to increased risk for lung disease, heart disease, and vasculitis, or inflammation of the blood vessels. Eye disease and neurological problems are also common comorbidities (conditions that occur at the same time) of RA.