Monitoring Disease Severity and Medication Response
To determine the progression of the disease or how it is responding to treatment, doctors sometimes use some of the same tests they use to diagnose arthritis. For example, a joint fluid test may show that an infectious agent has been eradicated by antibiotics. Or a “sed rate” test may be conducted a number of times to determine if inflammation is subsiding.
Salicylate level – This test measures the amount of salicylate (the main ingredient in aspirin and in some other NSAIDs ) in the blood to determine if enough is being absorbed to effectively reduce inflammation. The test can also determine if the level of salicylate is high enough to create dangerous side effects.
Muscle Enzyme tests (CPK, aldolase) – Muscles that have been damaged by some rheumatic diseases release certain enzymes into the blood, and these enzymes can be detected through blood tests. Such tests can measure the amount of muscle damaged as well as how effective medication has been in reducing the inflammation that caused the muscle damage.
Creatinine test – This test is used to determine the extent of kidney function by measuring the level of creatinine, a normal waste product of the muscles, in the blood. A test showing a high level of creatinine means that the kidneys are not working well enough to remove waste products from the body. Doctors may use this test to monitor kidney function in people with lupus or in those taking medications that could affect the kidneys.
Checking for Drug Side Effects
Often a drug side effect is obvious – you become nauseated, develop a rash or experience blurred vision or ringing in your ears. In other cases, the effects progress unnoticed – until a liver is damaged or a silent ulcer begins to bleed dangerously. For that reason, doctors often use lab tests to check for side effects – before they become major problems. The following tests are the most common
Liver enzyme tests ( SGOT, SGPT, bilirubin, alkaline phosphatase ) – These tests, which measure levels of liver enzymes in the blood, can help doctors determine if certain medications have caused damage to the liver.
Hematocrit (HCT) and hemoglobin (Hgb) – These tests measure the number and quality of your red blood cells. Low counts may suggest that your medications are causing gastrointestinal bleeding.
White blood cell count – A blood test showing a low number of infection-fighting white blood cells may suggest that your medication is decreasing your supply of white blood cells and, thus, your body’s chances of fighting infection.
Platelet count– This test measures the number of platelets, or “sticky” cells, that help the blood to clot. A low number of platelets could suggest that your medication has put you at risk of bleeding heavily.
Lab Tests’ Limitations
Despite their many benefits, lab tests have their limitations. Some may show negative results even when a person has the disease being tested for; others may be positive in people who don’t have – or may never develop – a particular disease. In the early stages of rheumatoid arthritis, for instance, only one in five people tests positive for rheumatoid factor; 15 to 20 percent of people without ankylosing spondylitis have the HLA-B27 genetic marker.
Not all forms of arthritis can be confirmed by lab tests. Other tests, including X-rays and magnetic resonance imaging, may be required to diagnose osteoarthritis, determine the cause of chronic back pain or examine internal organs affected by some forms of arthritis.
Even so, lab tests are essential to the diagnostic and treatment process. The right tests, along with your doctor’s own observations and your participation in the process, can help you get the safest and most effective treatment for your disease.