LAB TESTS FOR RHEUMATIC DISEASES

Blood tests

You'll probably have more blood tests than any other type of tests because blood is the most easily and safely sampled body tissue and contains traces of material from every other part of the body. The most common blood tests include the following:

Hematocrit (HCT) and hemoglobin (Hgb) counts measure the number and quality of red blood cells. If you have chronic inflammation, the number of red blood cells usually is low. (Inflammation is a body process that can result in pain, swelling, warmth, or redness.) Low hematocrit and hemoglobin counts may be signs that your medication is causing a loss of blood from your stomach and passing through your bowel. Low counts also may indicate a decrease in red blood cell production.

White blood cell count (WBC) measures the number of white blood cells. When you have an infection, your body makes more white blood cells. Some medications can decrease the number of white blood cells, which could increase your chances of getting an infection.

Platelet count measures the number of "sticky" cells or platelets that help the blood to clot. (Aspirin and some other medications make the platelets less "sticky.") If the number of platelets is low you could have too much bleeding. Some powerful arthritis medications in rare instances lower the platelet count.

Erythrocyte sedimentation rate (ESR), also called "sed rate," determines if you have inflammation. The sed rate can measure the amount of inflammation present. The test measures how fast red blood cells cling together, fall, and settle toward the bottom of a glass tube in an hour's time, like sediment. The higher the sed rate, the greater the amount of inflammation. As inflammation responds to medication, the sed rate usually goes down. This is an example of a test a doctor might order several times. Another test used to measure this is the C-Reactive Protein (CRP) test.

Salicylate level measures the amount of salicylate in the blood to find out if enough is being absorbed to reduce inflammation. (Salicylate is the main ingredient in aspirin and some other NSAIDs.) This is a helpful test for people who are taking large doses of these medications for a long time. High salicylate levels can be harmful, with or without such symptoms as ringing in the ears, nausea, vomiting, or even fever.

Muscle enzyme tests (CPK, aldolase) measure the amount of muscle damage. (In some rheumatic diseases, damaged muscles release certain enzymes into the blood.) These tests also can show how effective medication has been in reducing inflammation that causes muscle damage.

Liver enzyme tests (SGOT, SGPT, bilirubin, alkaline phosphatase) measure the amount of liver damage. Certain medications used in the treatment of arthritis can damage the liver. Aspirin, for example, has been known in rare instances to damage the liver, especially in children or in people who have had previous liver damage. Other NSAIDs can cause liver inflammation (hepatitis). Methotrexate can cause liver damage, especially in people who drink alcohol.

The creatinine test measures kidney function. Creatinine is a normal waste product of the muscles. A high level of it means that the kidneys are not working well enough to remove waste products from the body. The uric acid test measures the amount of uric acid in the blood. People with gout usually have high levels of uric acid, which forms into crystals that are then deposited in the joints and other tissues. However, not everyone with a high uric acid level has gout.

Immunological Blood Tests

The immune system is the body's natural defense against foreign invaders, such as bacteria or viruses. Occasionally, the immune system breaks down and loses the ability to distinguish between its own body cells and foreign invaders. When an invader such as a virus enters the body, the virus creates what is called an antigen. The body's immune system fights the antigen by creating an antibody. When the immune system fights against its own body cells, it creates autoantibodies that attack the body itself. Antinuclear antibodies are autoantibodies that react against the nuclei (core) of the body's own cells when these cell parts are mistaken for foreign invaders.

Rheumatoid factor (RF, Latex) measures whether a certain amount of abnormal antibody called rheumatoid factor is in the blood. The majority of people with rheumatoid arthritis (a common disease of inflamed joints that can cause joint alignment problems and loss of function) have a large amount of rheumatoid factor in their blood. However, up to 20 percent of adults with rheumatoid arthritis may never have any rheumatoid factor in their blood. In contrast, about 85 percent of children with juvenile rheumatoid arthritis (ERA) are negative for rheumatoid factor. ERA is a group of diseases, similar to rheumatoid arthritis, that begin in childhood.) It is important to note that having a positive rheumatoid factor will assist in the diagnosis, but the test alone is not conclusive.

The antinuclear antibody test (ANA) detects a group of autoantibodies that are found in most people with lupus and scleroderma and in a few people with rheumatoid arthritis. These autoantibodies react with antigens in the nuclei of cells. The antibodies suggest that an autoimmune illness may be present, although many people test positive and have little evidence of serious disease. Specific antinuclear antibody tests are helpful in the diagnosis of certain rheumatic diseases that involve abnormalities in the immune system. The names of the following tests are abbreviations of more complicated-sounding tests. The diseases for which they are used include:
* systemic lupus erythematosus (multiple-system illness, may involve the skin, joints, kidney, etc.); anti-dsDNA, anti-Sm, anti-Ro/SS-A, and antihistone tests help confirm the diagnosis.
* scleroderma (a marked thickening of the skin); the anti-Scl-70 test helps confirm the diagnosis.
* polymyositis (inflammation of muscles, resulting in muscle weakness, sometimes with joint inflammation); anti-Jo-l and anti-PM-l tests may help confirm the diagnosis.
* Sjogren's syndrome (disorder marked by dry eyes and dry mouth); anti-Ro/SS-A and anti-La/SS-B tests may help confirm the diagnosis.
* mixed connective tissue disease (a syndrome with a variety of symptoms, including joint inflammation and swollen fingers); the anti-Ul RNP test helps confirm the diagnosis.

Complement tests measure the amount of complement proteins circulating in the blood. Complement tests involve the reaction of antibodies with antigens. These tests usually are reserved for diagnosing or monitoring people with active lupus. Those people with lupus frequently have lower-than-normal amounts of complement, especially if the kidneys are affected.

Human leukocyte antigen (HLA) tissue typing tests detect the presence of certain "genetic markers" or traits in the blood. For example, B-27 is a genetic marker that nearly always is present in people with ankylosing spondylitis (a disease involving inflammation of the spine and sacroiliac joint) and Reiter's syndrome (a disease involving inflammation of the urethra, eyes, and joints). This test also is positive in five to 10 percent of the healthy population.

Urine Tests

Several different tests may be done on a urine sample to determine its contents. The tests show whether the urine contains red blood cells, protein, or a variety of abnormal substances, none of which is normally present. The detection of these substances may indicate kidney damage in certain rheumatic diseases, such as lupus. Some medications, such as gold and penicillamine, can cause protein to be lost through the urine. A 24-hour urine test evaluates all the urine collected over a 24-hour period. Sometimes the creatinine passed in a 24-hour urine specimen is measured to provide a clearer picture of kidney function than the creatinine blood test. Uric acid, calcium, and protein tests sometimes must also be done on a 24-hour sample.

Joint Fluid Tests

Inserting a needle into a joint and aspirating, or removing, synovial fluid from it can provide a doctor with valuable information. (Synovial fluid is the slippery fluid that fills a joint, providing smoother movement.) Usually this procedure is done in the doctor's office. It generally causes no more pain than drawing blood. An examination of the fluid may reveal what is causing the inflammation, such as uric acid crystals, a sure sign of gout, or bacteria, a sign of infection. crystals are found, proper medication may be prescribed. If an infection is found, the specific bacteria that are causing it can identified and the most effective antibiotic can be prescribed.

In addition, aspiration sometimes can relieve the pain of a badly swollen joint. Usually a corticosteroid is injected through the needle (if an infection is not present) to reduce inflammation for an extended period of time-up to three months in many cases and for months or years in a few instances. Corticosteroid are a group of drugs related to hydrocortisone, a natural hormone produced in the body. They are NOT the same as the steroids some athletes take. Corticosteroid are very helpful in reducing inflammation.

Biopsies

To help confirm a diagnosis or check on the status of disease activity, a doctor may order a biopsy, or removal small piece of tissue, to be examined under a microscope. Three of the most common biopsies include skin, muscle, and kidney biopsies. Skin biopsies usually are done to aid the diagnosis of lupus; vasculitis (inflammation of blood vessels); psoriatic arthritis (inflammation of joints and scaly, inflamed skin), or other forms of arthritis that involve the skin. After using a local anesthetic, a tiny piece of skin is removed.

Muscle biopsies are similar to skin biopsies, except the surgeon must go deeper into tissue. Muscle biopsies are used to look for signs of damage to the muscle fibers. This information can help confirm the diagnosis of polymyositis or vasculitis.

Kidney biopsies usually are done to check for signs of damage from a disease such as lupus. They usually are done by passing a needle through the back and withdrawing a bit of tissue for examination. Other biopsies are done on a less frequent basis. These include synovial, lung, salivary gland, and blood vessel biopsies. Liver biopsies occasionally are done to check for signs of damage in people receiving methotrexate for rheumatoid arthritis.


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