No one test can “prove” that a person has RA, or any other autoimmune disease for that matter. Instead, RA is diagnosed only after your doctor has performed a full history and physical exam and administered a few tests, such as the antinuclear antibody (ANA) test. You should consider the following facts when thinking about your ANA test results.
No one test can “prove” that a person has RA. Instead, RA is diagnosed only after your doctor has performed a full history and physical exam and administered a few tests, such as the antinuclear antibody test.
First, ANAs can be “normal.” These auto-antibodies are found in approximately 5% of the normal (i.e., without RA) population, usually in low titers (low levels). These persons usually experience no joint symptoms and have no disease. ANA titers less than 1:80 are less likely to be significant, and ANA titers less than or equal to 1:40 are considered negative. Even higher titers are often insignificant in persons who are more than 60 years of age.
Second, certain medications may lead to elevated ANA titers. Before taking this test, you should inform your doctor if you are taking any of the following medications, as they can interfere with the accuracy of the test:
- Hydralazine (Apresoline), procainamide (Procan, Pronestyl, Promine), and certain anticonvulsants (Dilantin, Mysoline)
- Antibiotics (isoniazid, penicillin, tetracycline), birth control pills, lithium, and some diuretics, such as chlorthalidone (Hygroton)
- Heart or blood pressure medications, such as acebutolol (Sectral), captopril (Capoten), atenolol (Tenormin), metoprolol (Lopressor), lovastatin (Mevacor), and quinidine
- Steroids, which may cause a false-negative result
Third, elevated ANA titers may be found in patients with the following non-arthritic diseases:
- Infections (viral or bacterial)
- Lung diseases (primary pulmonary fibrosis, pulmonary hypertension)
- Gastrointestinal diseases (ulcerative colitis, Crohn's disease, primary biliary cirrhosis, alcoholic liver disease)
- Hormonal diseases (Hashimoto's autoimmune thyroiditis, Graves' disease)
- Blood diseases (idiopathic thrombocytopenic purpura, hemolytic anemia)
- Cancers (melanoma, breast, lung, kidney, ovarian, and others)
- Skin diseases (psoriasis, pemphigus)
Your doctor should ask you about any other illnesses you have during your medical history. If reading this list reminds you of a disease you've had in the past, let your doctor know.
Your physician will be aware of the limitations of the ANA test. For instance, your physician knows that a positive ANA test may or may not be significant in a given individual, but merely helps to support a diagnosis that is based on your clinical history and physical examination. A positive ANA test helps to support a diagnosis of RA if you have physical signs and symptoms of the disease. The ANA is highly sensitive but nonspecific, however, so it produces a high number of false-positive results.
In the past, before the limitations of ANA tests were well understood, these tests were ordered frequently but not always appropriately. Unfortunately, a positive ANA test in an otherwise healthy person often began a time-consuming and expensive search for a nonexistent autoimmune disease, causing a lot of needless worry and anxiety on the part of the patient. Today, an ANA test is rarely ordered unless your physician has a strong suspicion that you are suffering from an autoimmune disease, such as RA.