Diagnosis

Diagnosis

Rheumatoid arthritis can be difficult to diagnose. Many other conditions resemble it and its symptoms can develop insidiously. Blood tests and x-rays may show normal results for months after the onset of joint pain. Even after rheumatoid arthritis has been diagnosed, it is extremely important to determine whether the course of the disease is benign (type 1) or aggressive (type 2) in order to treat the problem appropriately.

Blood Tests

Various blood tests may be used to help diagnose RA, determine its severity, and detect complications of the disease.

Rheumatoid Factor. In RA, antibodies that collect in the synovium of the joint are known as rheumatoid factor. In about 80% of cases of RA, blood tests reveal rheumatoid factor. It can also show up in blood tests of people with other diseases. However, when it appears in patients with arthritic pain on both sides of the body, it is a strong indicator of type 2 RA. The presence of rheumatoid factor plus evidence of bone damage on x-rays also suggests a significant chance for progressive joint damage.

Erythrocyte Sedimentation Rate Test. An erythrocyte sedimentation rate (ESR or sed rate) measures how fast red blood cells (erythrocytes) fall to the bottom of a fine glass tube that is filled with the patient's blood. The higher the sed rate the greater the inflammation. In addition to rheumatoid arthritis, the sed rate can be high in many conditions ranging from infection to inflammation to tumors. The test is used, then, not for diagnosis, but to help determine how serious the condition is.

C-Reactive Protein. High levels of C-reactive protein (CRP) are also indicators of active inflammation. However, because obesity also increases CRP levels, the doctor should consider a patient’s body mass index when evaluating CRP levels during RA diagnosis.

Anti-CCP Antibody Test. The presence of antibodies to cyclic citrullinated peptides (CCP) can identify RA years before symptoms develop. In combination with the test for rheumatoid factor, the CCP antibody test is the best predictor of which patients will go on to develop severe RA. Used in Europe, the test is now beginning to be used somewhat more commonly in the U.S. U.S. laboratories have not yet developed consistent standards for interpreting the test, however.