After a medical history is given and a physical examination is performed, your doctor may still need more information. Laboratory tests, especially blood tests, can provide a lot of information beyond what the medical history or physical examination can provide. You should ask your doctor about the tests being ordered. It will help you understand the diagnostic process and know what your doctor is looking for, rather than feeling unsure about the orders you have in hand. By ordering blood tests, your doctor is able to not only confirm a diagnosis, but monitor disease activity and the effectiveness of your medications or treatments. Through blood tests he can also be alerted to any side effects possibly caused by your medications
There are blood tests that you should expect your doctor to order when you are first being evaluated and some which will continue to be ordered routinely. Laboratory tests are important but not perfect diagnostic tools.
There can be false positive or false negative blood-test results. You may have arthritis, but tests may not reveal it, especially at first. On the contrary, you may have a blood test result suggestive of arthritis but never have the disease.
Rheumatoid factor (RF) is an antibody or immunoglobulin present in about 70 to 80 percent of adults who have rheumatoid arthritis. Some people with other chronic inflammatory conditions, and up to 5 percent of healthy individuals, are also positive for rheumatoid factor.
The test for rheumatoid factor is performed using latex agglutination or nephelometry. If your test result is positive for rheumatoid factor, your blood sample is further analyzed using serial dilutions to obtain a
A negative result for the rheumatoid factor test does not exclude the possibility of having rheumatoid arthritis. About 20 percent of people with rheumatoid arthritis are negative for rheumatoid factor and classified as having seronegative rheumatoid arthritis.
Erythrocyte Sedimentation Rate
The erythrocyte sedimentation rate (ESR) is commonly referred to as sedimentation rate or sedrate. The test is an indicator of the presence of nonspecific inflammation. The patient's blood sample is placed in a special graduated tube and allowed to sit undisturbed for an hour. Red cells fall at a faster rate if inflammation is present.
The normal value for sedrate is less than or equal to 10mm/hour for men and less than or equal to 20 mm/hour for women. Normal ranges do increase with age. Though the test is not specific regarding the origin of the inflammation, it is used as an indicator of severity of inflammation.
C-Reactive Protein (CRP)
C-reactive protein is a protein produced by the liver following tissue injury. Plasma levels of CRP increase quickly following periods of acute inflammation or infection, making this test a better indicator of disease activity than the sedrate, which changes more gradually. In chronic diseases, the test is used to monitor the effectiveness of treatments. The normal level of CRP is less than 1.0 mg/dl.
Anti-Cyclic Citrullinated Peptide Antibody Test (Anti-CCP)
The anti-cyclic citrullinated peptide antibody anti-CCP that become more common. The test is ordered if rheumatoid arthritis is suspected. Moderate to high levels of anti-CCP in a patient's blood confirm the diagnosis of rheumatoid arthritis. The test is more specific than rheumatoid factor, which can be positive even though a person doesn't have rheumatoid arthritis. Higher levels of anti-CCP also predict a more severe course of rheumatoid arthritis.
Antinuclear Antibodies (ANA)
Antinuclear antibodies (ANA) are abnormal autoantibodies (immunoglobulins against nuclear components of the human cell). The test is sometimes referred to as FANA or fluorescent antinuclear antibody test since it is based on indirect immunofluorescence.
Moderate to high antinuclear antibody levels are suggestive of autoimmune disease. Low levels are seen in about 5 percent of healthy adults. Positive antinuclear antibody tests are seen in:
More than 95 percent of systemic lupus erythematosus patients
60 to 80 percent of systemic sclerosis (scleroderma) patients
40 to 70 percent of patients with Sjögren's syndrome
30 to 80 percent of patients with polymyositis or dermatomyositis
20 to 60 percent of patients with Raynaud's phenomenon
30 to 50 percent of rheumatoid arthritis patients
5 to 25 percent of patients with discoid lupus
Positive ANA test results are reported in titers and patterns. Common patterns include homogeneous, speckled, nucleolar, centromere, and cytoplasmic. The pattern, which is viewed on specially prepared slides under a fluorescent microscope, has become less significant since more specific autoantibody tests have been developed.
Antinuclear antibodies can be negative during remissions or periods of low disease activity. Since ANA titers are increased during flares, the ANA test can reflect disease activity and help formulate disease prognosis. However, if the ANA is positive, it typically is always positive, so it may not be the best blood test to follow disease activity.
Complete Blood Count and Platelet Count
The complete blood count determines the WBC (white blood-cell count), RBC (red blood-cell count), hemoglobin, hematocrit, and several red blood-cell indices. Elevated white blood-cell counts suggest the possibility of an active infection. Patients taking corticosteroids may have an elevated WBC due to the medication. Chronic inflammation can cause a low red blood-cell count. Low hemoglobin and hematocrit may be indicative of anemia associated with chronic diseases or possible bleeding caused by medications. The platelet count is often high in rheumatoid arthritis patients, while some potent arthritis medications can cause platelets to be low.
It is possible for a rheumatoid arthritis patient to have a normal CRP and sedrate. In rare cases, there appears to be low sensitivity or inability to trigger the liver to produce inflammatory proteins required for both tests.
HLA Tissue Typing
Human leukocyte antigens (HLA) are proteins on the surface of cells. Specific HLA proteins are genetic markers for some of the rheumatic diseases. Patients may be tested to see if they have the genetic markers. HLA-B27 has been associated with ankylosing spondylitis and other spondyloarthropathies. Rheumatoid arthritis is associated with HLA-DR4.
Elevated levels of uric acid in the blood (known as hyperuricemia) can cause crystals to form, which are deposited in the joints and tissues, causing painful gout attacks. Uric acid is the final product of purine metabolism in humans. Not everyone who has elevated uric acid will develop gout. A blood uric-acid level greater than 7 for men and greater than 6 for women is considered elevated. Elevated uric acid can result from excess production in the body or insufficient elimination.