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Autoimmune Disease: Use of ANA & Antibody Tests for Diagnosis
Free Test Guide from Quest
Autoimmune diseases are difficult to diagnose; their symptoms can be vague, vary from patient to patient, and often overlap. Moreover, there is no single diagnostic test for any one autoimmune disease. Diagnosis is most often based on a compilation of clinical information, family history, data from laboratory testing, and, in some cases, imaging tests. Laboratory tests include relatively nonspecific antinuclear antibody (ANA) testing and/or tests for individual antibodies that are more disease specific.
Antinuclear antibody is a marker of inflammation and autoimmune processes and, as such, is a general marker of autoimmune disease. Therefore, it is a good first test for suspected autoimmune disease. Several methods of ANA testing are available, including immunofluorescence assay (IFA), enzyme-linked immunosorbent assay (ELISA), and multiplex immunobead assay. The American College of Rheumatology (ACR) recommends using an IFA with HEp-2 cells, because the test is highly sensitive. This sensitivity stems from the number of autoantigens (up to 150) in the HEp-2 cells. The nuclear and cytoplasmic fluorescence patterns suggest certain types of autoimmune disease. Although these patterns are not specific for a particular disease type, the information may aid diagnosis. A positive ANA result does not necessarily indicate presence of an autoimmune disease. Healthy individuals, particularly as they age, and those with certain infectious diseases or cancer, may have positive results. Therefore, ANA test results must be reviewed in the proper clinical context.
Immunoassay-based specific antibody tests are less sensitive than ANA IFA for antinuclear and anticytoplasmic autoantibody screening; however, they are often more specific for a particular autoimmune disease than is ANA IFA. Therefore, specific antibody tests can be used to aid in differential diagnosis. In sum,
- ANA by IFA is gold standard as an initial test. This test is very sensitive and if positive this provides a titer and pattern. Higher titers indicate greater likelihood of disease.
- ANA antibodies by multiplex measures specific antibodies which cause various ANA IFA patterns and helps physicians specifically pin point what specific antibodies are present. Testing for antibodies alone will miss ANA related diseases.
- Optimal approach is to order ANA IFA with reflex to antibodies cascade panel, because it initially screens by highly sensitive test and only if positive it reflexes for relevant antibodies in the cascade panel. Thus,this combines the power of both high sensitivity and high specificity to rule in or rule out autoimmune disease. The ANA IFA screen in combination with reflex testing to specific autoantibody tests can be used effectively for differential diagnosis with one blood draw for the patient.
The test guide discussed the approaches to testing, provides an algorithm for the primary care physician, and a convenient table of autoantibody prevalence in autoimmune diseases.