Erythrocyte Sedimentation Rate (ESR)
The erythrocyte sedimentation rate is a test which involves placing a blood sample in a tube and determining how fast the red blood cells settle to the bottom in one hour. When inflammation occurs the body produces proteins in the blood which make the red cells clump together. Heavier cell aggregates fall faster than normal red cells. For healthy individuals, the normal rate is up to 20 millimeters in one hour. Inflammation increases the rate significantly. Since inflammation can be caused by conditions other than arthritis, the sedrate test alone is not diagnostic.
Rheumatoid Factor (RF)
Rheumatoid factor is an antibody found in unusually large amounts of patients with rheumatoid arthritis. Rheumatoid factor was discovered in the 1940's and became a significant diagnostic tool in the field of rheumatology. 80% of RA patients have RF in their blood. Usually, the higher concentration of RF, the more severe the rheumatoid arthritis. RF can take many months to show up in a patients blood. If tested too early in the course of the disease, the result could be negative and retesting should be considered at a later date. There are also patients with all the signs and symptoms of RA but are seronegative for RF. Some doctors suspect another disease masquerading as RA in these cases. RF can occur in response to inflammatory of infectious diseases other than RA, though usually in these cases, the amount is lower.
White blood cells may be typed for the presence of HLA-B27. This test is common in medical centers because it is needed for transplants. What has been found is that this genetic marker is present in some forms of arthritis, chiefly ankylosing spondylitis and Reiter's syndrome.
Antinuclear Antibody (ANA)
ANA (antinuclear antibody) test is performed to help detect certain rheumatic diseases. Patients with certain diseases, especially lupus, make antibodies to the nucleus, or command center, of the body's cells. These antibodies are called antinuclear antibodies and are tested for by placing a patient's blood serum on a microscope slide containing cells with visible nuclei. A substance containing fluorescent dye is added which binds to the antibodies. Under a microscope the abnormal antibodies can be seen binding to the nuclei.
- Over 95% of patients with lupus have a positive ANA test.
- 50% of rheumatoid arthritis patients are positive for ANA.
Patients with other diseases also can have positive ANA tests. Other criteria must be involved in definitive diagnosis.
C-Reactive Protein (CRP)
C-Reactive Protein measures the concentration in blood serum of a special type of protein produced in the liver that is present during episodes of acute inflammation or infection.
As a blood test, CRP is not specific. A high result serves as a general indication of acute inflammation. In cases of inflammatory rheumatic diseases, such as rheumatoid arthritis and lupus, doctors can utilize the CRP test to assess the effectiveness of a specific arthritis treatment and monitor periods of disease flareup.
Lupus Erythematosus (LE)
The LE cell test is not commonly performed anymore. Its initial discovery opened up the whole field of antinuclear antibodies though. Only 50% of lupus patients are found to have positive LE tests. Therefore the test does not identify 50% of patients as having the disease.
Anti-CCP (anti-cyclic citrullinated peptide antibody) is a new and exciting blood test to help doctors confirm a diagnosis of rheumatoid arthritis.
Anti-DNA and Anti-Sm
Lupus patients have antibodies to the heredity material DNA (deoxyribonucleic acid). It is a useful diagnostic tool since it is unusual to find these antibodies in people who do not have lupus. The test is also a good monitoring tool since the levels of anti-DNA rise and fall with disease activity.
Lupus patients also have antibodies to Sm, another substance in the cell's nucleus. These antibodies also occur only in lupus patients. The test is not particularly useful in monitoring disease activity however.
The complement system is a complex set of blood proteins which are part of the body's defense system. These proteins are inactive until an antibody binds to an antigen and activates the complement system. The system produces factors which help destroy bacteria, and combat invaders with white cells. These reactions consume complement and leave depressed levels indicative of immune complex formation. Lupus patients often show decreased levels of total complement. The complement test may be helpful in tracking the disease activity of a lupus patient.
The Duke University Medical Center Book of Arthritis, David S. Pisetsky, M.D., Ph.D.