Rheumatoid arthritis is an autoimmune disease caused by the immune system of the body attacking the lining of the joints. Rheumatoid arthritis, a chronic condition that can last a lifetime, causes inflammation of the joints that result in pain, stiffness and even loss of function. Rheumatoid arthritis affects approximately 1.3 million Americans, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases, and it can develop at any age. There is no specific test to definitively diagnose rheumatoid arthritis, but there are several blood tests that can contribute to a successful diagnosis.
Erythrocyte Sedimentation Rate
An erythrocyte sedimentation rate (ESR) test, also referred to as a sed rate, is a blood test that measures the body's inflammatory response. To perform the test, blood is taken from a vein, EDTA (ethylenediaminetetraacetic acid) may be added to prevent coagulation, and then the blood is diluted with 4 parts of citrate (a salt solution) to 1 part blood. The mixture is then put into a vertical tube and observed to determine how many red blood cells fall to the bottom, referred to as sedimentation and how long it takes.
The faster the red blood cells fall to the bottom of the tube, the more inflammation that is present in the body. Although the Arthritis Foundation reports that only about 60 percent of patients with rheumatoid arthritis have an increased ESR, the test is still utilized to determine the presence and severity of the condition. It may also be performed periodically to determine the effectiveness of treatments.
C-Reactive Protein
The C-reactive protein (CRP), a protein produced in the liver that increases when there is inflammation in the body, is another test to help measure inflammation in the body. This test is also not specific for rheumatoid arthritis, but when performed with the ESR test can help to diagnose and monitor the disease.
To perform the CRP test, blood is drawn from a vein and mixed with antiserum, which has various substances that specifically react with different proteins. The more CRP detected, the more inflammation that is present in the body.
Rheumatoid Factor
Many people who have rheumatoid arthritis develop an antibody called the rheumatoid factor. This antibody, a specific protein created by the immune system to fight off a foreign substance, is not present in all cases of rheumatoid arthritis, but its presence can help to diagnose the disease or the severity of the disease. Approximately 70 to 80 percent of patients who are seropositive, meaning they test positive for rheumatoid factor, have rheumatoid arthritis, according to the Arthritis Foundation.
