Autoimmune rheumatic diseases are conditions in which the immune system attacks the joints and certain systems. They are often difficult to diagnose, as their symptoms can be vague, vary from patient to patient, and often overlap. Laboratory testing can provide useful information, but no single test provides a definitive diagnosis for any one rheumatic disease. Diagnosis is most often based on a compilation of symptoms and signs, including clinical information and laboratory test results.
Testing for antinuclear antibodies (ANAs) using an immunofluorescence assay (IFA) is a good first approach for laboratory evaluation of patients suspected of having certain autoimmune rheumatic diseases. ANAs, a group of autoantibodies directed against diverse nuclear and cytoplasmic antigens, are associated with several autoimmune rheumatic diseases.
- systemic lupus erythematosus (SLE),
- systemic sclerosis (SSc),
- and mixed connective tissue disease (MCTD).
ANA testing may also be helpful in evaluating Sjögren syndrome and polymyositis/dermatomyositis. Individuals with rheumatoid arthritis (RA) or other rheumatoid disorders may be positive or negative for ANAs. Knowing the ANA titer can be helpful in interpreting positive ANA results.
For patients with positive ANA screening results, nuclear and cytoplasmic antibody fluorescence patterns can be used to evaluate the likelihood of certain autoimmune diseases. These patterns may inform the differential diagnosis, although they may not be specific for individual antibodies or diseases. For example, a homogenous nuclear pattern may be associated with SLE, drug-induced SLE/vasculitis, or juvenile idiopathic arthritis (JIA), while a diffuse cytoplasmic pattern could be consistent with SLE or an inflammatory myopathy.
Given the range of conditions associated with positive ANA IFA results, positive results are not highly specific for any single condition. Tests for individual antibodies may offer greater specificity and are often needed to help establish the diagnosis.
The combination of the highly sensitive ANA IFA screen, followed by specific autoantibody testing when the IFA is positive, can help maximize sensitivity as well as specificity.
A positive ANA result in conjunction with clinical suspicion suggests, but does not necessarily confirm, the presence of an autoimmune disease. Positive results are not uncommon in healthy individuals (particularly as they age) and those with certain infectious diseases or cancer.
In cases with strong clinical suspicion, specific antibody testing may be appropriate even if the ANA IFA result is negative.
A positive ANA IFA result with a positive result for 1 or more of the specific antibodies may suggest the presence of a certain autoimmune disease.
Tests for other autoimmune diseases may be considered if clinically indicated; these include autoimmune hepatitis, primary biliary cholangitis, autoimmune thyroiditis, Addison’s disease, pernicious anemia, autoimmune neuropathies, vasculitis, celiac disease, and bullous disease.
A negative ANA IFA result suggests the absence of many autoimmune diseases, but does not rule them out. Thus, specific autoantibody testing may be considered for patients with negative ANA IFA results if clinical suspicion is high (eg, Jo-1 for suspected polymyositis/dermatomyositis, SS-A for suspected Sjögren syndrome). A positive result on the RF, CCP antibody, or 14-3-3n tests generally supports a diagnosis of early or established RA, or potential subclinical RA. In ANA-negative patients, positive results are consistent with early RA. A negative result on all 3 tests is consistent with absence of RA (sensitivity = 78%), although early RA cannot be ruled out. If clinically indicated, a negative test result may also be followed up with tests for other autoimmune diseases.
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