Rheumatoid Arthritis Blood Tests - What Do They Mean?
RF. ESR. Anti-CCP. ANA. CPR. No, these aren’t codes used by secret agents to communicate their missions. They’re names of blood tests used in diagnosing and managing rheumatoid arthritis. When you’re new to this disease, they can seem as mysterious and impenetrable as a secret language. What do they measure? What do the numbers mean? What’s normal, what isn’t? This post is all about demystifying RA blood tests.
RA Blood Tests
There are a number of blood tests that can be used when doctors are trying to find out if you have RA, as well as indicators of how the disease is managed. Some of the most common blood tests are:
Rheumatoid Factor (RF). RF is a type of antibody that may be associated with inflammation. This is usually one of the first tests your family doctor will order if they suspect you might have inflammatory arthritis. However, it’s important to know that 20-30 percent of people with RA are negative for RF (also called seronegative). It can also be positive in other conditions, including Sjogren’s and tuberculosis and a small percentage of healthy people may also test positive. Normal results can be reported in two ways, less than 40-60 u/mL or less than 1:80 (1 to 80) titer (titer expresses level of concentration).
Antinuclear antibody (ANA). The ANA is another blood test used when doctors suspect inflammatory arthritis. If positive, it is an indication that more specific investigation is necessary to identify the particular type of inflammatory arthritis. It is especially found in people who have lupus, but is also present in RA, certain infections, gastrointestinal diseases and so on. Results are reported in a titer and low levels are in the range of 1:40 to 1:60.
Erythrocyte Sedimentation Rate (ESR). Also called sed rate, the ESR measures how fast red blood cells cling together and settle into a sediment. The higher the rate, the more inflammation is present in the body. Normal levels are less than 15 mm/hr in men and less than 20 mm/hr in women.
C-Reactive Protein (CRP). Along with the ESR, the CRP tests the level of inflammation in the body. It measures the concentration of a particular protein which is created in the liver during periods of acute inflammation. The normal range is approximately less than 1.0 mg/dL or less than 10 mg/L.
Anti-Cyclic Citrullinated Peptide (Anti-CCP). The CCP is an antibody that can indicate the presence of RA. It’s a newer, much more accurate test. When it is positive, there is a 90 to 95 percent likelihood that the person has RA. As well, it can be positive up to 15 years before a person develops RA. The range of results are:
Negative: less than 20.0 U
Weak positive: 20.0-39.9 U
Positive: 40-59.9 U
Strong positive: more than or = 60.0 U
During the diagnosis process, you may also be tested for Lyme disease, which can include symptoms of fever, fatigue and joint pain, as well as for anemia, which can often occur with certain inflammatory chronic illnesses. As you are treated for RA, it’s also likely that you may be tested for liver and kidney function, as well as cholesterol. This helps your doctor keep an eye on your internal organs to stay ahead of any systemic issues.
Vectra DA. This is a relatively new test, used in the management of rheumatoid arthritis in able who have already been diagnosed. It measures 12 biomarkers associated with RA activity and is considered much more accurate than the CRP or ESR. Your score will fall on a range from 0-100:
Low disease activity 1-29
Moderate disease activity 30-44
High disease activity 45-100
What Does It All Mean?
Now that you know what the tests measure and what the numbers mean, how do you use that information? Not as much as you might think. With the exception of the anti-CCP test, blood tests are not very accurate. Relying on them as the determining factor in diagnosis or in assessing your state of health can be misleading. In fact, most rheumatologists use them only as a confirming tool for diagnosis and a guideline during treatment.
For instance, if you get a copy of your blood tests and notice that CRP or ESR is high, you might be extremely worried about a flare. The fact is that these tests measure general inflammation in the body, not specifically RA inflammation. They’ll go up if you are flaring, but they also go up if you are brewing a sinus infection. It’s much more likely that your rheumatologist will focus on a physical examination and your report of your pain levels and quality of life to assess how you’re doing. Keep this in mind if you start to worry about your numbers. If your pain and energy levels are decent and your joints don’t show the usual signs of disease activity (for most, this includes swollen joints), you’re probably OK.
It is your right to have a copy of your lab work. In fact, it’s probably a good idea to keep your records in a binder, should you have to change doctors or see a new specialist. Be aware of what blood tests mean, but try not to obsess. Poring over your numbers or indulging your inner geek by considering graphing the results over time is probably not very healthy. Instead, talk to your doctor to get more information and support about blood tests.
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Lene writes the award-winning blog The Seated View. She’s the author ofYour Life with Rheumatoid Arthritis: Tools for Managing Treatment, Side Effects and Pain and 7 Facets: A Meditation on Pain.