Antibodies to nuclear antigens (ANA), screening
Why this test?
For screening of autoimmune diseases, such as systemic connective tissue diseases, autoimmune hepatitis, primary biliary cirrhosis, etc. For diagnosing systemic lupus erythematosus, assessing its activity, making a prognosis and monitoring its treatment.
In what cases is it prescribed?
With symptoms of an autoimmune process: prolonged fever of unclear origin, pain in the joints, skin rash, unmotivated fatigue, etc.
With symptoms of systemic lupus erythematosus (fever, skin lesions), arthralgia / arthritis, pneumonitis, pericarditis, epilepsy, kidney damage.
Every 6 months or more often when examining a patient diagnosed with SLE.
When prescribing procainamide, disopyramide, propafenone, hydralazine and other drugs associated with the development of lupus drugs.
Antibodies to nuclear antigens (ANA) are a heterogeneous group of autoantibodies directed against components of one's own nuclei. They are found in the blood of patients with various autoimmune diseases, such as systemic connective tissue diseases, autoimmune pancreatitis and primary biliary cirrhosis, as well as with some malignant neoplasms.
The ANA test is used as a screening for autoimmune diseases in a patient with clinical signs of an autoimmune process (long-term fever of unclear origin, joint syndrome, skin rashes, weakness, etc.). Such patients with a positive result of the analysis need further laboratory examination, which includes more specific tests for each autoimmune disease (for example, anti-Scl-70 in case of suspicion of systemic scleroderma, antibodies to mitochondria in case of suspicion of primary biliary cirrhosis). It should be noted that a negative ANA test result does not exclude the presence of an autoimmune disease. ANA are most characteristic of patients with systemic lupus erythematosus (SLE).
They are detected in 98% of patients, which allows us to consider this study as the main test for diagnosing SLE. The high sensitivity of ANA for SLE means that repeated negative results make the diagnosis of SLE doubtful.
At the same time, the absence of ANA does not completely exclude the disease. In a small part of patients, ANA is absent at the time of onset of SLE symptoms, but occurs during the first year of the disease. In 2% of patients, antibodies to nuclear antigens are never detected. If the test result is negative in a patient with symptoms of SLE, it is advisable to conduct more specific laboratory tests for SLE, primarily for antibodies to double-stranded DNA (anti-dsDNA). Detection of anti-dsDNA in a patient with clinical signs of SLE is interpreted in favor of the diagnosis of SLE even in the absence of ANA. SLE occurs as a result of a complex of immunological disorders that develop over a long period of time.
The degree of imbalance of the immune system gradually increases with the course of the disease, which is reflected in the increase in the spectrum of autoantibodies.
The first stage of the autoimmune process is characterized by the presence of genetic features of the immune response (for example, certain alleles of the major histocompatibility complex, HLA) in the absence of laboratory test abnormalities.
At the second stage, it is possible to detect autoantibodies in the blood, while there are no clinical signs of SLE. Antibodies to nuclear antigens, as well as anti-Ro-, anti-La-, antiphospholipid antibodies are most often detected at this stage. Detection of ANA is associated with a 40-fold increase in the risk of SLE. The period between the appearance of ANA and the development of clinical symptoms is variable and averages 3.3 years. Patients with a positive ANA test result are at risk for developing SLE and require periodic follow-up by a rheumatologist and laboratory testing.
he third stage of the autoimmune process is characterized by the appearance of symptoms of the disease, while it is possible to detect the widest range of autoantibodies in the blood, including anti-Sm antibodies, antibodies to double-stranded DNA and ribonucleoprotein.
Thus, to obtain complete information about the degree of immunological disorders in SLE, the ANA test must be supplemented with an analysis of other autoantibodies.
The course of SLE varies from persistent remission to fulminant lupus nephritis. Different clinical and laboratory criteria are used to give a prognosis of the disease, to evaluate its activity and the effectiveness of treatment.
Since none of the tests can clearly predict exacerbations or damage to internal organs, monitoring of SLE is always a comprehensive assessment that includes the study of ANA, as well as other autoantibodies and some general clinical indicators. In practice, the doctor independently determines a set of tests that most accurately reflect how the course of the disease changes in each patient.
Drug-induced lupus is a special clinical syndrome. It develops against the background of taking some drugs (most often procainamide, hydralazine, some ACE inhibitors and beta-blockers, isoniazid, minocycline, sulfasalazine, etc.) and is characterized by symptoms reminiscent of SLE. ANA can also be detected in the blood of most patients with lupus. If a patient taking these drugs has symptoms of an autoimmune process, an ANA test is recommended to rule out this type of lupus.
The peculiarity of lupus drugs is the disappearance of immunological disorders and symptoms of the disease after complete withdrawal of the drugs - at this time, a control study of ANA is recommended ANA are found in 3-5% of healthy people (in the group of patients older than 65 years, this figure can reach 10-37%). A positive result in a patient without symptoms of an autoimmune process must be interpreted taking into account additional anamnestic, clinical and laboratory data.