A positive ANA result in conjunction with clinical findings is diagnostic therefore frequently asked by the clinician in case of suspected CTD. Since different ANA are associated with one or other CTD a systematic approach has to be followed while performing these tests. Therefore initially screening is carried out usually by IF-ANA/ELISA and if positive more specific tests are performed based on clinical findings and IF-ANA staining patterns (table ).
Autoantibody to dsDNA is specific and diagnostic for SLE and levels are elevated during active disease. Therefore in a case of suspected SLE if homogenous pattern is observed on IF-ANA further tests i.e. CLIF, ELISA, blotting tests etc. may be done to confirm dsDNA. Similarly anti-Sm is highly specific for SLE and needs confirmation by other tests i.e. Blotting etc. but is present in only 10% of SLE cases.
Anti-SSA/Ro antibody although more common in Sjogren's syndrome but can also be found in 30% cases of SLE with cutaneous involvement. Therefore if IF-ANA shows speckled/peripheral pattern further tests i.e. Blotting, MIA are required for detection of anti-SSA/Ro antibody. Clinical significance and detection methods for anti-SSB/La are similar to that for anti-SSA/Ro except that it is less common and may indicate minor course of disease. While presence of these two autoantibodies supports Sjogren's syndrome they are not much needed for diagnosis. Anti-Scl-70 autoantibody found in scleroderma (SS) gives a fine speckled staining pattern on IF-ANA and can be confirmed by immunodiffusion techniques but its detection is also not a necessity for diagnosis.
Antinucleolar antibodies are a group of autoantibodies which give nucleolar staining pattern. Most common of these are anti-PM-Scl, anti-RNA polymerase I-III and anti-U3-RNP (antifibrillarin). Although seen in scleroderma and polymyositis (PM) their detection is also not widely practiced [24
A protocol generally followed by the clinicians and step by step approach to detect all these autoantibodies has been described in figure . A summary of certain other guidelines [24
] to be considered are:
Algorithmic approach for ANA testing.
- ANA testing is not helpful in confirming a diagnosis of rheumatoid arthritis or osteoarthritis therefore should not be used in such conditions.
- ANA testing is not recommended to evaluate fatigue, back pain or other musculoskeletal pain unless accompanied by one or more of the clinical features in favor of a CTD.
- ANA testing should usually be ordered only once.
- Positive ANA tests do not need to be repeated.
- Negative tests need to be repeated only if there is a strong suspicion of an evolving CTD or a change in the patient's illness suggesting the diagnosis should be revised.
- A positive ANA test is important only in conjunction with clinical evaluation and in the absence of symptoms and signs of a CTD; a positive ANA test only confounds the diagnosis. A positive ANA test can also be seen in healthy individuals, particularly the elderly or in a wide range of diseases other than CTD, where it has no diagnostic or prognostic value.
Recommendations in the guidelines may further evolve over time, as newer analytic methods and additional clinical research yield important results.