What role does the laboratory play in the diagnosis of RA?The laboratory has a limited role in the diagnosis of RA. Unlike a disease like lupus, where patients make antibodies to several components of the body, the patient with RA has almost none. The only antibody that is common in patients with rheumatoid arthritis is the rheumatoid factor. Other antibodies may be present, but they do not necessarily indicate RA. In addition to the presence of antibodies, there are other laboratory findings that doctors may look for to help them diagnose RA, including anemia (low red blood cell count) and other blood cell count abnormalities. During the course of treatment, doctors often have to monitor the patient’s health with laboratory tests, as several of the drugs used to treat RA can affect the health of many organs.
What is the rheumatoid factor?The rheumatoid factor is an antibody directed against another antibody in the blood. It is present in about 60 percent of rheumatoid arthritis patients; however, its presence does not automatically indicate RA, as it is common to other disorders as well. Conversely, the absence of rheumatoid factor does not rule out a diagnosis of RA. When the rheumatoid factor is present in a RA patient, one is said to have sero-positive disease. When there is no rheumatoid factor, an RA patient is said to have sero-negative disease. Generally, sero-positive disease is more aggressive than sero-negative.
What is an ANA?ANA stands for antinuclear antibody. This antibody is directed against the nuclei of certain cells.
Is an ANA present in those with RA?Some RA patients have antinuclear antibodies, though the strength, or titer, of such antibodies is low. They are more common to other autoimmune conditions, though doctors must not overlook the possibility of rheumatoid arthritis when they detect ANAs. Too often doctors hastily make a diagnosis of lupus when they find ANAs without ruling out RA.
What is an ESR?ESR stands for erythrocyte sedimentation rate. The speed at which red blood cells settle to the bottom of a test tube helps doctors check for inflammation. The faster these cells settle, the more inflammation is present. The ESR is the test conducted to determine the rate at which the red blood cells settle.*26/141/5*
May 12, 2011
RHEUMATOID ARTHRITIS: BLOOD TESTS
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