Anti-nuclear antibodies (ANAs, also known as anti-nuclear factor or ANF) are autoantibodies directed against contents of the cell nucleus.[1]
They are present in higher than normal numbers in autoimmune disease. The ANA test measures the pattern and amount of autoantibody which can attack the body's tissues as if they were foreign material. Autoantibodies are present in low titers in the general population, but in about 5% of the population, their concentration is increased, and about half of this 5% have an autoimmune disease.
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One can check for the presence of ANAs in blood serum by means of a laboratory test. There are also additional tests that allow one to test for individual ANAs. The general ANA test is usually one of two types: indirect immunofluorescence or ELISA. The indirect immunofluoresence is considered to be the more accurate of the two, but the ELISA version is gaining popularity because of its lower cost.
The normal titer of ANA is 1:40 or less. Higher titers are indicative of an autoimmune disease. The presence of ANA is indicative of lupus erythematosus (present in 80-90% of cases), though they also appear in some other auto-immune diseases such as Sjögren's syndrome (60%), rheumatoid arthritis (30-40%), autoimmune hepatitis, scleroderma and polymyositis & dermatomyositis (30%), and various non-rheumatological conditions associated with tissue damage. Other conditions with high ANA titre include Addison disease, Idiopathic thrombocytopenic purpura (ITP), Hashimoto's, Autoimmune hemolytic anemia, Type I diabetes mellitus, Mixed connective tissue disorder.
The following table list the sensitivity of different types of ANAs for different diseases, in this case what percentage of those with the disease have the ANA. Some ANAs appear in several types of disease, resulting in lower specificity of the test.
| ANA type | Target antigen | Sensitivity | ||||||
|---|---|---|---|---|---|---|---|---|
| SLE | Drug-induced LE | Diffuse systemic sclerosis | Limited systemic scleroderma | Sjögren syndrome | Inflammatory myopathy | MCTD | ||
| All ANAs (by indirect IF) |
Various | >95 | >95 | 70-90 | 70-90 | 50-80 | 40-60 | 95[2] |
| Anti-dsDNA | DNA | 40-60 | - | - | - | - | - | -[2] |
| Anti-Sm | Core proteins of snRNPs | 20-30 | - | - | - | - | - | -[2] |
| Anti-histone | Histones | 50-70 | 90[2] - 95 | - | - | - | - | -[2] |
| Anti Scl-70 | Type I topoisomerase | - | - | 28-70 | 10-18 | - | - | -[2] |
| Anti-centromere | Centromeric proteins | - | - | 22-26 | 90 | - | - | -[2] |
| Anti-snRNP70 | snRNP70 | 30[3]-40[3][2] | -[2] | 15[2] | 10[2] | -[2] | 15[2] | 90[2] |
| SS-A (Ro) | RNPs | 30-50 | - | - | - | 70-95 | 10 | -[2] |
| SS-B (La) | RNPs | 10-15 | - | - | - | 60-90 | - | -[2] |
| Jo-1 | Histidine-tRNA ligase | - | - | - | - | - | 25 | -[2] |
| - = less than 5% sensitivity
Unless else specified in boxes, then ref is: [3] |
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Following detection of a high titer of ANAs (e.g. 1:160), various subtypes are determined.[4] This is typically done on cells of the HEp-2 cell line. Examples include
The LE cell was discovered in bone marrow in 1948 by Hargraves et al.[5] This was the first indication that processes affecting the cell nucleus were responsible for lupus erythematosus (LE). In the 1950s, progressively more sensitive and specific ANA serology tests became available.
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