Blood tests rheumatoid arthritis
by Nathan Wei, MD, FACP, FACR
Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.
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A patient who is being evaluated for rheumatoid arthritis will usually have the following tests performed:
•The complete blood count is a test that quantifies the number of red blood cells, white blood cells, and platelets. Blood consists of these components suspended in a fluid called plasma. Automated machines rapidly count the cell types.
The white cell count is normally between 5,000-10,000. Increased values suggest inflammation or infection. Exercise, cold, and stress will temporarily elevate the white cell count. Normal values for the red cell count vary with gender. Males normally have values around 5-6 million per microliter. Females have a lower normal range at 3.6-5.6 million red cells per microliter.
Hemoglobin, which carries oxygen, is also measured in a complete blood count. The normal hemoglobin value for males is 13-18 g/dl. Normal for females is 12-16 g/dl. The hematocrit measures the percent of total blood volume which is red cells. Normal value for males is 40-55%, and the normal value for females is 36-48%. Generally, the hemoglobin times 3 equals the hematocrit. Decreased values are indicative of anemia.
The MCV, MCH, MCHC are red cell indices which indicate the size and hemoglobin content of red cells. These indices may provide clues as to the probable cause of an existing anemia. Platelets are components which are important in clot formation. Normal values range from 150,000-400,000.
Inflammation can cause changes in the blood count. The red cell count may go down, the white cell count may go up, and the platelet count may be elevated. While anemia may occur with inflammatory arthritis it may be caused by other things such as blood loss or iron deficiency.
The percent and absolute number of each type of white blood cell is called the differential. Neutrophils are increased in bacterial infections and acute inflammation. Lymphocytes are increased in viral infections. Monocytes are increased in chronic infections and eosinphils are increased in allergies.
•The chemistry panel is a series of tests which are used to evaluate overall health. The tests include a battery of tests that evaluate liver and kidney function. For example, a patient with a high creatinine level may have a problem with the kidneys. Creatinine is a waste product found in the blood. Certain types of inflammatory arthritis can affect kidney function. Certain arthritis drugs can affect kidney function too. Uric acid is another test of the blood chemistry panel which, if elevated, may be indicate gout.
•The erythrocyte sedimentation rate is a test that measures the presence of systemic inflammation. Inflammation increases the rate significantly. Since inflammation can be caused by conditions other than arthritis, the sed rate test alone is not diagnostic. C-reactive protein is another test that measures inflammation and is more sensitive and tends to rise more quickly and fall more quickly than the sed rate.
•Rheumatoid Factor is an antibody found in a large number 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 the 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 done during the course of the illness. There are also patients with all the signs and symptoms of RA but are seronegative for RF. RF can occur in response to other conditions such as endocarditis, leprosy, and sarcoidosis. There are three types of rheumatoid factor, IgM, IgA, and IgG. IgM is the most common. All three should be tested for since a significant number of patients with rheumatoid arthritis will have other types of rheumatoid factor besides IgM.
•Another test, the anti-cyclic citrullinated peptide antibody, or anti-CCP is a more specific test than rheumatoid factor. If present in a patient at a moderate to high level, it not only confirms the diagnosis but also may indicate that the patient is at increased risk for damage to the joints. Anti-CCP and rheumatoid factor should both be obtained in a patient undergoing diagnostic workup.
It should be mentioned that the absence of rheumatoid factor and anti-CCP early in the disease process doesn’t necessarily rule out the diagnosis of rheumatoid arthritis.
•Patients with certain rheumatic 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. Under a microscope the abnormal antibodies can be seen binding to the nuclei. More than 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.
•Thyroid function tests are also performed if there is suspicion of thyroid disease. Thyroid disease can aggravate joint symptoms.
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