Double-stranded DNA (dsDNA), antibodies
Why this test?
For diagnosis, assessment of activity and control of systemic lupus erythematosus treatment;
For differential diagnosis of diffuse connective tissue diseases.
In what cases is it prescribed?
With symptoms of systemic lupus erythematosus: fever, skin lesions (butterfly erythema or red rashes on the face, forearms, chest), arthralgia / arthritis, pneumonitis, pericarditis, epilepsy, kidney damage;
when antinuclear antibodies are detected in the serum, especially if a homogeneous or granular (dotted) type of immunofluorescence of the nucleus is obtained;
Antibodies to double-stranded DNA (anti-dsDNA) belong to the group of antinuclear antibodies, that is, autoantibodies directed by the body against components of its own nuclei. While antinuclear antibodies are characteristic of many diffuse connective tissue diseases, anti-dsDNA is thought to be specific for systemic lupus erythematosus (SLE). The detection of anti-dsDNA is one of the criteria for the diagnosis of SLE.
It is possible to detect anti-dsDNA with the help of immunoenzymatic analysis. The high sensitivity (about 100%) of this test is necessary when examining samples with a low amount of antibodies. Given the fact that in the blood serum of patients with systemic connective tissue diseases, several types of autoantibodies can be present at the same time, as well as the fact that most often the differential diagnosis of these diseases is based on the detection of any specific type of antibodies, when choosing a laboratory test, it is extremely it is important to consider the high specificity. The specificity of anti-dsDNA analysis is 99.2%, which makes this study indispensable in the differential diagnosis of SLE.
Anti-dsDNA is detected in 50-70% of patients at the time of SLE diagnosis. It is believed that immune complexes consisting of double-stranded DNA and antibodies specific to it (immunoglobulins IgG and IgM) are involved in the development of microvasculitis and determine the characteristic symptoms of SLE in the form of damage to the skin, kidneys, joints and many other organs. Anti-dsDNA is so typical for SLE that it allows diagnosing this disease even with a negative result of a screening test for antinuclear antibodies. However, it should be noted that the absence of anti-dsDNA does not exclude the presence of SLE.
The detection of anti-dsDNA in a patient without clinical signs and other criteria of this disease is not interpreted in favor of the diagnosis of SLE, but such patients are at risk of developing SLE in the future and need to be monitored by a rheumatologist, since the appearance of anti-dsDNA can precede the onset of the disease during several years
The concentration of anti-dsDNA varies depending on the features of the course of the disease. As a rule, a high indicator indicates high activity of SLE, and a low one indicates the achievement of remission of the disease. Therefore, measuring the concentration of anti-dsDNA is used to control the treatment and prognosis of the disease. An increase in concentration indicates insufficient control of the disease, its progression, as well as the possibility of the development of lupus-nephritis. On the contrary, a stable low concentration of antibodies is a good prognostic sign. It should be noted that such dependence is not observed in all cases. The level of anti-dsDNA is measured regularly, every 3-6 months, in the case of mild severity of SLE and at shorter intervals in the absence of disease control, when selecting therapy, against the background of pregnancy or the postpartum period.
Drug-induced lupus is a special clinical syndrome. Despite the significant similarity of the clinical picture of this condition with SLE, this type of lupus has a number of differences: it is provoked by taking drugs (procainamide, hydralazine, propylthiouracil, chlorpromazine, lithium, etc.) and completely resolves after their cancellation, rarely involves internal organs and therefore has a more favorable prognosis and is also less often combined with the presence of anti-dsDNA. Therefore, with a negative result of the anti-dsDNA analysis in a patient with clinical signs of autoimmune lupus and the presence of an antinuclear factor, drug-induced lupus should be excluded.
Despite the fact that a high level of anti-dsDNA is characteristic of SLE, their low concentration is also found in the blood of patients with some other diffuse connective tissue diseases (Sjogren's syndrome, mixed connective tissue disease). In addition, the test may be positive in patients with chronic hepatitis B and C, primary biliary cirrhosis, and infectious mononucleosis.
The spectrum of autoantibodies in SLE also includes other antinuclear (anti-Sm, RNP, SS-A, SS-B), antispasmodic antiphospholipid antibodies. Their detection in the blood serum of a patient with clinical signs of SLE along with anti-dsDNA also helps in making the diagnosis. In addition, the determination of the concentration of anti-dsDNA should be supplemented by some general clinical tests.