3) Blood and urine tests
Patients may be asked for blood and urine tests by their doctors. Physical examination is usually not enough to make a precise diagnosis, so doctors may refer you to the lab to get tested. Although there is not a specific test that confirms whether patients have or have not rheumatoid arthritis, there are other tests that may indicate the presence of inflammation or immune disorder. A blood sample is drawn from your vein by a nurse or a health care professional and sent to a lab to perform the following tests:
- Complete blood count (CBC) test is done to measure the number of blood cells especially white blood cells (WBCs) which represent immune response against pathogens and self-tissue in case of autoimmune disease. Rheumatoid arthritis patients are reported to have an elevated number of WBCs which attack small joints and cause inflammation. CBC is relatively cheap, and most doctors ask their patients to do it.
- C-reactive protein (CRP) is also a common test which doctors ask for to measure the degree of inflammation. C-reactive protein is made by the liver and excreted in response to inflammation. Unfortunately, C-RP is not specific to rheumatoid arthritis, therefore doctors cannot rely on in diagnosing. Rheumatologists use the CRP test not only for diagnosing but also in evaluating drug’s effectiveness and potency.
- Rheumatoid factor test is the newest among the previous tests. Rheumatoid factor (RF) is an antibody that contributes to attacking healthy joint tissue. The rheumatoid factor test is considered the most accurate test in diagnosing rheumatoid arthritis as its specificity is estimated to range from 60% to 80%. More than 75% of adult patients with a rheumatoid factor are reported to have an elevated level of rheumatoid factor in their blood. The more elevated the RF level is in the blood, the worse is the condition of rheumatoid arthritis. RF test is also used in evaluating drug medications’ effectiveness.
- Erythrocyte (red blood cell) sedimentation rate is the least used test to measure the degree of inflammation. ESR test involves putting a certain quantity of blood in a test tube and measure the amount of precipitated red blood cells after one hour. RBCs tend to descend and precipitate more in case of inflammation. Erythrocyte sedimentation rate (ESR) is normally up to 22mm/hr for men and 29mm/hr for women.
- Urine test is used as an additional test. Some rheumatologists ask patients to have a urine test to measure the amount of uric acid to distinguish between rheumatoid arthritis and gout. Gout symptoms are similar to RA, but gout is characterized by elevated uric acid. Doctors exclude gout if uric acid level is normal in the urine.