What Your Rheumatoid Arthritis Lab Results Mean
ANA, CRP, CCP, CBC and more: HealthCentral interviewed Dr. Joel Kremer, Pfaff Family Professor of Medicine at Albany Medical College in Albany, N.Y. about diagnosing rheumatoid arthritis and what lab results can mean. The bottom line: Rheumatoid arthritis cannot be diagnosed on the results of lab tests alone.
Q: How do most patients get referred to a rheumatologist in the first place? Kremer: Usually, it's the pain that's perceived to be arthritis pain. Sometimes it's muscle pain. Other times it can just be a nagging pain from anywhere that the primary care provider cannot diagnose. It's more helpful to be referred to a rheumatologist when there are other symptoms along with the pain, such as early joint swelling.
Q: What does the rheumatologist do when they see a referred patient? Kremer: We'll take a history. Do you have morning stiffness? Fatigue? How long has this been going on? Do you have any family history of these same symptoms? After history, you do a physical exam looking for impaired joint movement, which joints are swollen, warm to the touch, difficult to move.
Q: When do you take lab tests? And which tests do you start with first? Kremer: It depends on where the initial history and exams lead you. You many test for Rheumatoid factor (RF), CCP-Antibody, ANA, which can be seen in lupus as well. Depending on your area of the country and how long the symptoms have been going on, you may want to get a Lyme Disease titer. You'd also want to get a sedimentation rate, a red blood cell count and other tests such as white blood cell counts, test for anemia and a C-reactive protein test, which can be a measure of disease activity.
Q: Let's talk about each test and what they're testing for. What does Rheumatoid factor tell you? Kremer: It's an antibody that will eventually be found in about 80% of patients diagnosed with rheumatoid arthritis. But, about 20% to 30% of patients that will ultimately be diagnosed with rheumatoid arthritis will not have an RA factor in their blood when they are first tested and they may never have it.
Q: What's the CCP test? Kremer: It's cyclic citrullinated peptides. Citrullinated peptides are correlated with disease progression and activity. It becomes a marker of disease severity if it's present. Most healthy patients don't have CCP antibodies. The CCP is a sensitive test, and there are patients who may test positive for it that did not test positive for RA factor. Of course, a patient could test positive for both.
Q: What about the ANA test? Kremer: The anti nuclear antibody test. ANA may be found in people with lupus. It's also associated with other diseases, such as liver disease. It's a non-specific test, though. If it's positive, you'd follow up with more specific tests for lupus.
Q: What does erythrocyte sedimentation rate tell you? Kremer: It's a very rough marker for inflammation. It can be elevated in the presence of an infection of any kind or in the presence of a malignancy.
Q: It's interesting that you haven't emphasized numbers, normal vs. abnormal or high numbers for these test results. Kremer: It's very, very important to understand that rheumatoid arthritis is not diagnosed on the basis of a lab test. A positive result or a high number is not an "A-ha! You got this on a lab test, so you have this diagnosis." The diagnosis is based on medical history, physical exams and the lab tests can be helpful to confirm what was found. For example, is you test positive for RF or CCP, it would be inappropriate to label you with RA unless you had other elements found in the medical history or physical exam.
Q: So when you're lab tests don't necessarily confirm (or refute) a diagnosis of rheumatoid arthritis, what should you do? Kremer: You really need to have a discussion with your rheumatologist about what is going on, considering all the elements that were found in your exam and all the other disease conditions that the specialist is familiar with.