|
Why Does My Rheumatologist Order An ANA Test? Antinuclear antibodies (ANA) are commonly seen in autoimmune diseases. While a positive ANA is not diagnostic of a particular autoimmune condition, it is seen often in diseases such as systemic lupus erythematosus (SLE), systemic sclerosis, Sjogren’s disease, polymyositis, including rheumatoid arthritis. Roughly 90 per cent of people with SLE could be ANA positive at some time during the course of their illness. Who including where the ANA is performed is critically important. Many expert rheumatologists could have a particular office lab that is skilled in performing the ANA test properly. Often, commercial laboratories could have staff people who are not as experienced in ANA interpretation. The ANA is a screening test that is very sensitive for the diagnosis of SLE. On the flip side, though, it is associated with many false positive test results, particularly at the time the ANA is at a low level. Usually, ANA levels of 1:80 or lower have less significance than higher levels do. However, the interpretation pertaining to the ANA must be made in combination with the patient’s history, physical examination, including other information in order to make a proper diagnosis. ANAs additionally have patterns. These patterns sometimes point towards a diagnosis but are usually not specific. 1 pattern that seems to be relatively specific is the anti-centromere pattern which is seen in conditions such as systemic sclerosis or limited cutaneous sclerosis. The nucleolar pattern is additionally associated with Raynaud’s phenomenon including systemic sclerosis. Other patterns such as diffuse or speckled are not very specific. Rarely, a rim or peripheral pattern may be seen in patients with SLE. If a patient has a positive ANA including other clinical signs, then more specific laboratory testing is required. Tests for these more specific antigens (proteins) are usually performed using what is called the ELISA technique. Antibodies to double-stranded DNA are fairly specific for SLE since 70 per cent of patients with SLE could have antibodies to double-stranded DNA at some point during their illness. High levels of antibodies to double-stranded DNA indicate more severe disease including additionally a higher likelihood of kidney disease. Measurements of antibodies to double stranded DNA change with disease activity so that the measurement should be repeated for monitoring purposes. Anti-Sm antibody (anti-Smith) additionally is specific for SLE but is present in only regarding 30 per cent of patients with the disease. RNP antibodies are seen in patients who have a condition known as mixed connective tissue disease (MCTD). Antibodies to SSA including SSB (also known as Ro including La) should be seen with main Sjogren’s disease including SLE. Other useful tests are antihistone antibodies which are seen with drug-induced lupus, anti-Scl-70 which is seen in systemic sclerosis, including anti-Jo-1 which is seen with dermatomyositis. If these specific antibodies are performed as a quantitative measure, meaning a number representing the amount of antibody is given, then it is often useful to repeat these tests for monitoring purposes. Where these more specific tests are performed is again important. If done in a laboratory where skilled technicians are performing the tests, then the reliability is much higher than if they are performed in a general commercial laboratory. Commercial laboratories handle a tremendous amount of volume as well including there have been instances at the time wrong results are given because of a mix up with specimens.
|