There are a number of laboratory tests that a rheumatologist may order when seeing a patient for the first time. This is particularly true if rheumatoid arthritis (RA) is suspected. The reason so many laboratory tests are needed is because of the complexity involved in arriving at the correct diagnosis. Oftentimes, diseases can look similar. Disease may evolve over time and sometimes they overlap.
The following is a rundown of the different tests that can be ordered and why.
Erythrocyte Sedimentation Rate (ESR). This test-also known as the sed rate" measures how fast the red blood cells settle to the bottom of a tube in 1 hour. Inflammation causes the red cells to clump together and therefore settle faster. The rate in normal individuals is up to 20 mm in 1 hour. Inflammation increases this rate so that a patient with a disorder such as active rheumatoid arthritis will often have a sed rate much higher than 20mm.
C-Reactive Protein (CRP). CRP measures a protein produced by the liver that is present during acute inflammation or infection. The CRP test can be used to monitor the effectiveness of treatment as well as to monitor disease flares.
Both of these tests correlate with x-ray damage due to RA and long-term disability; persistent elevations of these blood markers suggest a poor prognosis.
ESR is usually elevated in inflammatory arthritis, but can be less useful than the CRP, because the ESR rises more slowly and falls to normal more slowly once inflammation is controlled. The CRP tends to rise faster and go down faster than the sed rate in response to inflammation. Also, in very early inflammatory disease, both the ESR and CRP may not be elevated, so normal levels do not rule out the presence of significant disease. These tests are essential to get at baseline, because there is evidence they may be useful in predicting disease severity or response to therapy.
Rheumatoid Factor (RF). RF is an immunoglobulin. It is in the IgM category of antibodies and is directed against another type of antibody type called IgG. It is present in about 70% of patients with RA. Unfortunately, an elevated level of RF can be seen in about 10% of normal people. Additionally, in roughly 20% of patients with RA, the RF is not elevated, and so a negative test result does not rule out RA as a cause of the patient's symptoms. The presence of RF correlates with aggressive and erosive disease. And high levels of RF appear to suggest a worse prognosis. RF can take months to develop, and some RA patients remain negative for RF throughout the course of their illness.
Other autoimmune diseases that can be associated with a positive RF include systemic lupus erythematosus, Sjogren's disease, polymyositis, dermatomyositis, scleroderma, and mixed connective tissue disease. Infections and other diseases can also be associated with a positive RF. These include sarcoidosis, tuberculosis,endocarditis, hepatitis (especially hepatitis C), syphilis, osteomyelitis, infectious mononucleosis, and cirrhosis. A positive RF would not usually be seen in types of arthritis such as gout, osteoarthritis, ankylosing spondylitis, and psoriatic arthritis,.
Anticyclic Citrullinated Peptide Antibody (anti-CCP). This is a relatively new blood test thaqt helps to confirm a diagnosis of RA. Anti-CCP appears to be more specific for RA. Anti-CCP antibody is present in approximately 30% of RF negative RA (seronegative RA). Testing with the combination of anti-CCP antibody and RF may be better for ruling out RA than using either test alone.
High levels of anti-CCP are seen in severe and progressive disease.
Antinuclear Antibody (ANA). The ANA test can help detect SLE. However, an elevated ANA is not specific, and can be seen in disorders other than lupus, including a significant percentage of patients with RA. More than 95% of patients with lupus have a positive ANA test. A more specific test for SLE is the presence of antibodies to DNA (anti-DNA). It is unusual to find antibodies to DNA (anti-DNA) in people who do not have lupus. Levels of anti-DNA vary with disease activity.
Antibodies to Sm, RNP, Ro (SSA), La (SSB). Lupus patients also have other antibodies to different cell nuclear components. Antibodies to Sm occur only in patients with lupus while antibodies to RNP occur in patients with mixed connective tissue disease, and antibodies to Ro and La may occur in patients with Sjogren's disease.
Creatine phosphokinase (CPK). CPK is a muscle enzyme that is elevated in a number of types of inflammatory conditions, particularly inflammatory muscle diseases such as polymyositis and dermatomyosotis. Since these conditions can also present with arthritis, a CPK is a good test to order.
Thyroid function tests. Thyroid disease often is present in patients with inflammatory arthritis. It is because autoimmunity seems to be involved in the development of both of these problems. An underactive thyroid (hypothyroidism) can also cause aches and pains and muddy the diagnostic waters". With severe thyroid disease, elevations in CPK may be seen.
Complete Blood Cell Count (CBC). Chronic inflammation can lead to an anemia. This is a common occurrence in patients with rheumatoid arthritis. Also, some of the non-steroidal anti-inflammatory drugs (NSAIDS) which patients with RA take can cause ulcers which can lead to blood loss. Also, a low white blood cell count may be a sign of drug toxicity or another disease process such as lupus. Also, it is good to have a baseline result to help with drug monitoring
Chemistry Panel. Viral hepatitis can present with inflamed joints. It is important to make sure that liver function test results are normal. It is a good idea to have a baseline in case potentially liver damaging medications such as non-steroidal anti-inflammatory drugs or methotrexate are used. Another organ system, the kidney can also be affected not only by diseases such as lupus or Sjogren's disease but also is a target for drug toxicity. NSAIDS are the chief culprits. Also, if a patient's kidney function isn't normal it will affect the rate of elimination of some drugs that are used to treat rheumatoid arthritis. Drug toxicity then becomes an issue.
Viral Hepatitis Panel. As mentioned above, viral hepatitis can present with an inflammatory form of arthritis. Prior to starting any medicine that can adversely affect the liver, it is important to have a baseline in regard to chronic hepatitis B and C infections. Before using anti-TNF medications and rituximab (Rituxan), the rheumatologist must check hepatitis status, especially in regards to hepatitis B because these drugs can cause aggravation of hepatitis B.
Urinalysis. A urine sample is studied for protein, red blood cells, white blood cells, or casts. These abnormalities may indicate kidney damage due to lupus or vasculitis. Use of some medications, because they can injure the kidneys, require initial as well as ongoing screening for urinary abnormalities.
Complement levels. Complement is a serum protein that is important in the assessment and monitoring of different types of autoimmune disease. Lowered levels of complement (C3, C4) are indicative of immune complex formation (where an antibody binds to an antigen- a foreign protein) and complement binding. Lupus patients often show decreased levels of total complement, which may be helpful in tracking disease activity.
X-rays. X-rays of hands, wrists, feet, and knees are useful for detecting the presence of erosions. If erosions are seen, especially in early disease, this suggests the diagnosis of RA or other erosive diseases, and can indicate a more aggressive disease process.
Magnetic Resonance Imaging (MRI). MRI is more sensitive than x-rays for detecting inflammation within the joint and also for detecting early erosions in RA.
Diagnostic Ultrasound (DUS). Ultrasound is a relatively new technology in the realm of musculoskeletal diseases. It is an effective, fast, and cost-effective means of detecting early inflammation and damage in patients with different types of arthritis.
Chest X-ray. A chest x-ray (CXR) in patients with early RA will likely be normal. However, because RA-related lung disease can be present early and may be difficult to detect on physical exam, it is reasonable to obtain a baseline CXR to evaluate if signs of lung disease are present. In addition, because some agents, such as methotrexate and anti-TNF drugs, which are used to treat RA can lead to lung toxicity, getting a baseline CXR before starting medication therapy is reasonable.
Not all of the above tests will necessarily be ordered at the first visit. But this is a good basic list that will give the reader a good idea of what to expect.
Another issue is the laboratory. If the rheumatologist has his or her own specialty laboratory and it is state-certified as a reference lab, I would highly recommend that a patient get their lab tests done at that office. A rheumatologist will have the best idea as to lab test interpretation and the rheumatologist's lab will be experienced in dealing with arthritis. They will provide the most accurate and believable results. All too often, large commercial labs are not used to dealing with the complexity of arthritis testing. A correct diagnosis is key!
