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 with other clinical conditions. The diagnosis of autoimmune disease is based on patient signs and symptoms, clinical information, and laboratory test results. Testing of the antinuclear antibody (ANA) is a good first approach for laboratory evaluation of patients suspected of having certain autoimmune rheumatic diseases.
ANAs are a class of antibodies that bind to cellular components in the nucleus including proteins, DNA, RNA, and nucleic acid-protein complexes. The origin of ANA testing was first described in 1948 when Hargraves and colleagues observed the LE cells, described as mature polymorphonuclear leukocytes containing phagocytosed nuclear material. LE cells were so named because there were found only in a patient with systemic lupus erythematosus (SLE). Since then, ANA identification remains the most sensitive serologic marker for evaluation of patients with suspected connective tissue autoimmune disorders including systemic lupus erythematosus (SLE), Sjogren’s syndrome, and polymyositis/dermatomyositis. Although 20-30% of the average population has detectable levels of ANAs, increased titers are characteristic of individuals with connective tissue disorders. The table below shows the rheumatic disease associated with a positive ANA test.
| Table 1. Rheumatic disease associated with a positive ANA test | |||
| Disease | Sensitivity | Specificity | |
| System Lupus erythematosus | 93-95 | 57 | |
| Sjogren’s syndrome | 48 | 52 | |
| Systemic Sclerosis | 85 | 54 | |
| Juvenile idiopathic arthritis | 57 | 39 | |
| Juvenile idiopathic arthritis with uveitis | 80 | 53 | |
| Rheumatoid arthritis | 41 | 56 | |
| Polymyositis/dermatomyositis | 61 | 63 | |
| Drug-induced Lupus* | NA | NA | |
| Mixed connective tissue disease* | NA | NA | |
*For both drug-induced lupus and mixed connective tissue disease, the diagnostic criteria require a positive ANA, and therefore specificity and sensitivity cannot be determined
Retrieved from https://pubmed.ncbi.nlm.nih.gov/22267099/
Thus, the sensitivity and specificity of methods used to detect ANAs are very important to diagnose patients with autoimmune rheumatic disease.
Solaris Diagnostics laboratory can now provide screening for ANA with a turnaround time of 24 hours from the time the sample is received in the laboratory.
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