Guide to Lab Tests
By Mary Anne Dunkin
Originally published in Arthritis Today

Lab tests are an integral part of life with arthritis. Learn exactly what your doctor is looking for when he orders a vial of blood or draws fluid form an inflamed knee.

More than for most other diseases, the diagnosis and treatment of arthritis requires a hands-on approach. By examining your tender joints and muscles and listening to your description of your symptoms and their severity, a doctor can usually get a pretty good idea of what is going on inside your body.

But there are times when a doctor needs information that only a laboratory examination of bodily fluids and tissues can reveal. When he needs to confirm a diagnosis, monitor disease progress or medications effectiveness, or determine if the drugs you're taking are causing potentially dangerous - but not evident - side effects, lab tests are in order.

The majority of lab tests are performed on blood because it is easily and safely sampled and it holds many microscopic clues to what's going on throughout the body. Other tests may require urine, joint fluid or event small pieces of skin or muscle. Whether you're just beginning the diagnostic process or completing your umpteenth year of treatment, the following information should help you understand some of the most common tests you're likely to encounter.

Making a Diagnosis
While lab tests aren't needed for every form of arthritis, they are very important to verify and confirm the presence of some diseases, according to Robert Lahita, MD, chief of rheumatology at St. Lukes/Roosevelt Hospital and associate professor of medicine at Columbia University. If your symptoms and physical examination  suggest rheumatoid arthritis (RA), lupus, Sjögren's syndrome, Lyme disease or one of a few other inflammatory forms of arthritis, the tests listed under "Making a Diagnosis" in the box above can often confirm your doctor's suspicions.

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. See tests listed under "Monitoring Disease Severity and Medication Response" in the box above.

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 reasons, doctors  often use lab tests to check for side effects - before they become major problems. Find the most common tests under "Checking for Drug Side Effects" in the box above.

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 RA, for instance, only one in five people tests positive for rheumatoid factor; 15 to 20 percent of people with RA never test positive. A small percentage of healthy people have a positive ANA , and about 5 to 10 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.