Blood tests or imaging studies to diagnose rheumatoid arthritis do not help to pinpoint the diagnosis, especially in the early stages. There are more than a hundred types of arthritis and this makes it that much more difficult.
The real help comes from the signs and symptoms elicited from the clinical history and examination. They help the doctor to diagnose rheumatoid arthritis with the blood tests and imaging studies, which also help to determine the extent of the damage to the involved joints.
For example, higher levels of rheumatoid factor (RA factor) in the blood indicate a higher level of inflammation.
1) Clinical history
Your doctor, ideally a rheumatologist, will take a detailed history of your symptoms and examine the joint for the classical signs, which will help him to diagnose RA. These include:
- Inflammation in the joint
- Characteristic joint swelling and stiffness in the morning
- Tenderness over the joint (pain on applying pressure over the joint)
- Symmetric polyarthritis — the same joints are involved on both sides of the body
- Findings of rheumatoid nodules under the skin, commonly over the elbows or fingers
- Joint deformity
(2) Blood tests to diagnose rheumatoid arthritis
- Erythrocyte Sedimentation Rate (ESR) is raised due to the presence of inflammation caused by rheumatoid arthritis.
- Red blood cell count decreases due to the presence of mild anemia, which is seen in about 33 to 66 percent of all RA patients.
- Platelet count increases due to inflammation. However, it can decrease due to side effects of drugs.
- C – Reactive proteins (CRP) are raised, again due to inflammation in an active RA. This test also helps to gauge disease activity and response to treatment.
- The rheumatoid factor also called the RA factor is present in about 50 to 80% of RA patients. Higher levels of RA factor indicate higher levels of inflammation.
- Antinuclear antibodies (ANA) is raised in about 40% of the RA cases. However, this is not a specific test for RA as ANA can be found raised in other diseases as well.
- Assessment of liver and kidney function is important for treatment options. For example, a patient with kidney insufficiency will not be prescribed a nonsteroidal anti-inflammatory drug (NSAID). Similarly, methotrexate is contraindicated in patients with liver disease such as hepatitis C and renal impairment.
(3) Imaging studies to diagnose rheumatoid arthritis
- X-rays of the involved joints show loss of bone density, erosion of the cartilage and edges of the bones. On x-ray, this shows as reduced joint space. Inflammation of soft tissues around the joints is also seen. Characteristic periarticular erosive changes may be indicative of a more aggressive rheumatoid arthritis disease.
- MRI is particularly useful in detecting the erosion of cartilage and bones of RA in the early stages.
- Bone densitometry is done to detect osteoporosis, which occurs in RA.
In 2010, the American College of Rheumatology and European League Against Rheumatism jointly created a new classification criteria for rheumatoid arthritis. Medscape.com gives a good account of it.