How is rheumatoid arthritis diagnosed?
Jul 8, 2019
What are the risk factors for developing rheumatoid arthritis? How can we avoid confusing it with another disease? What tests are used to make the diagnosis? Read our guide to learn everything you need to know about the diagnosis of rheumatoid arthritis.
The risk factors
Environmental, behavioural and genetic factors can contribute to the development of rheumatoid arthritis. Indeed, air pollution and smoking have been identified as risk factors and nearly 90% of patients with RA carry HLA DR4 (60%) or DR1 (30%) antigens.
The people most at risk are:
- People aged 40 to 60 (most frequent age of occurrence)
- Women, who are two to three times more affected than men
- People with a family member with rheumatoid arthritis (twice the risk of developing the disease)
Confusing RA with other diseases: differential diagnosis
The diagnosis of rheumatoid arthritis is not based on a simple test, but rather on a set of clinical, biological and radiological signs.
Some conditions may have similar symptoms but are not to be confused with rheumatoid arthritis. Among them, we can mention:
- Rhizomelic polyarthritis
- Rheumatic fever
- Ankylosing spondylitis
The clinical assessment necessary for the diagnosis
Here are the clinical signs that should indicate the presence of rheumatoid arthritis:
- Joint stiffness upon awakening of at least 30 minutes (commonly called "rusting")
- There are at least three painful joints in the wrists, hands or fingers
- Symmetry of joint damage (both wrists, both hands...)
- An awakening during the night due to joint pain
- The pressure on the forefoot joints is painful
- The presence of subcutaneous and inflammatory rheumatoid nodules
- To be symptoms of RA, these symptoms must have been present for at least 6 weeks.
The imaging check-up will allows doctors to look for signs of erosion or joint pinching. X-rays will be taken of all symptomatic joints. At the very beginning of the disease, x-rays will be normal. Subsequently, when the signs appear, these radiological examinations will have a double benefit: they will confirm the diagnosis and serve as a basis for comparison with subsequent radiological examinations, thus making it possible to monitor the evolution of the disease. Ultrasound or MRI can also be used as part of an imaging assessment.
The biological assessment
This biological test makes it possible to look for several elements, such as an inflammatory syndrome, the presence of auto-antibodies such as rheumatoid factor (RF) and cyclic citrullinated antipeptide antibodies, or antinuclear antibodies.
When the body detects substances that seem foreign to it, it sets up a defense strategy to recognise, destroy and eliminate them: this is the inflammatory reaction. The causes of inflammation are multiple: they can be of external origin (bacteria, viruses, skin lesions, blows...) or internal (autoimmune diseases such as rheumatoid arthritis, cancers...)
C-Reactive Protein (CRP) is an inflammatory protein, synthesised by the liver, which increases its blood concentration within a few hours in the event of inflammation. CRP plays an important role in mobilising and activating the immune defences (white blood cells) and stimulating the destruction process of cells considered as foreign (phagocytosis). The higher the CRP value, the more important the inflammatory response.
The erythrocyte sedimentation rate
To determine the erythrocyte sedimentation rate (ESR), a technician places the red blood cells in a test tube and determines the distance until they fall within a given time (usually one hour). In the event of an inflammatory reaction, the blood level of the inflammation proteins (including fibrinogen) increases and leads to the formation of red blood cell clusters. The higher the value of the SV, the heavier the aggregates are and the faster they fall to the bottom of the tube.
The search for antibodies
Blood testing also allows for the detection of antibodies that may indicate the presence of an autoimmune disease such as cyclic citrullinated antipeptides (anti-CCP antibodies), also known as Anti-citrullinated protein antibodies (ACPAs) (ACPA). Anti-CCP antibodies to cyclic citrullinated peptides are very interesting for the early diagnosis of rheumatoid polyarthritis. When this assay is positive, it can predict with a specificity greater than 95% the diagnosis of rheumatoid arthritis.
Rheumatoid factor: immunoglobin
The blood test also looks for rheumatoid factor (RF), an immunoglobulin, most often of the IgM type, with autoantibody activity directed against human immunoglobulins G (immunoglobulins are proteins that help the body defend itself against infections). RF does not directly cause joint damage, but induces the body's inflammatory response, which then contributes to joint destruction through an autoimmune mechanism. The RF assay is sensitive but not very specific, which implies that it may be positive in diseases other than rheumatoid arthritis. The discovery of this factor alone is therefore not sufficient to confirm the presence of rheumatoid arthritis. Moreover, the absence of these antibodies also makes it impossible to eliminate the diagnosis because the disease may be in an initial stage and the rheumatoid factor rarely appears at the beginning of the disease.
This biological test can be supplemented by tests exploring autoimmunity such as antinuclear antibody (ANA) testing and a complete blood count (CBC).
All these examinations combined with the patient's examination and a thorough examination will make it possible to establish the diagnosis of rheumatoid arthritis. Ask your doctor for advice if you suspect rheumatoid arthritis and if you have any questions about the results of your tests!
And how were you diagnosed? Have you been misdiagnosed? Do you suspect that you have undiagnosed RA?