Autoantibodies to microsomal liver and kidney antigens (LKM)
Why this test?
For differential diagnosis of autoimmune liver diseases (autoimmune hepatitis, primary biliary cirrhosis, primary sclerosing cholangitis).
For diagnosis of type 2 autoimmune hepatitis and control of its treatment.
To determine the treatment of patients with hepatitis C.
In what cases is it prescribed?
With symptoms of acute hepatitis: fever, pain in the right hypochondrium, jaundice.
With symptoms of chronic hepatitis: unmotivated weakness, anorexia, arthralgia, myalgia, diarrhea, discomfort in the abdomen, moderate itching, weight loss.
Before prescribing interferon alfa to patients with hepatitis C.
Anti-LKM is a heterogeneous group of autoantibodies characteristic of autoimmune hepatitis. They got their name (from the English Anti-liver kidney microsomal) due to the fact that they are able to interact with the enzymes of the microsomal oxidation system of the liver and kidneys.
There are several variants of these antibodies.
Anti-LKM-1 interacts with the enzyme cytochrome oxidase CYP 2D6. The main antigen for anti-LKM-2 is cytochrome oxidase CYP 2C9. Anti-LKM-3 is directed against the enzyme UDP-glucuronyltransferase-1. Anti-LKMs to cytochrome oxidase CYP 1A2 and CYP 2A6 are also described. Anti-LKM, along with antibodies to mitochondria and antibodies to smooth muscles, are most often found in patients with autoimmune liver diseases. It is still unclear whether these antibodies are the direct cause of the disease or are produced in response to hepatocyte damage.
The main method of detecting these autoantibodies is the indirect immunofluorescence reaction (INF). Enzyme immunoassay (ELISA) complements, but does not replace, RNIF. Different variants of anti-LKM have a different type of luminescence when examined by RNIF, which distinguishes them from each other and from other autoantibodies to liver components.
Therefore, anti-LKM research with the help of RNIF is carried out for the differential diagnosis of autoimmune liver diseases: primary biliary cirrhosis, primary sclerosing cholangitis, autoimmune hepatitis and cross syndromes. They have a similar clinical picture, which makes it impossible to distinguish them based on clinical signs.
The basis of differential diagnosis of these diseases is the study of antibodies to components of hepatocytes. So, for example, the detection of anti-LKM is more typical for autoimmune hepatitis, and the detection of antibodies to mitochondria - for primary biliary cirrhosis.
Depending on the presence of certain antibodies, autoimmune hepatitis is divided into several types. Detection of anti-LKM-1 allows to classify the disease as type 2. This variant of autoimmune hepatitis is more characteristic of children under the age of 15, affects girls more often and has a less favorable prognosis than types 1 and 3. CYP 2D6 has some antigenic similarity with the hepatitis C virus.
Perhaps for this reason, anti-LKM is more often found in the blood of patients infected with hepatitis C (in 6% of infected adults and 11% of children). Patients with hepatitis C, whose blood contains anti-LKM, often worsen their condition in response to interferon alpha therapy, and they require more careful selection of the drug dose and control of liver function.
Therefore, it is advisable to conduct anti-LKM research before prescribing hepatitis C therapy with interferon. It should be noted that the choice of the method of detection of these antibodies in this case plays a big role. For example, the study of anti-LKM in patients with hepatitis C using enzyme immunoassay (ELISA) is characterized by a higher frequency of false negative results compared to RNIF. Therefore, RNIF is the best method for detecting anti-LKM in patients with hepatitis C.
Despite the fact that the detection of anti-KLM is considered a characteristic feature of autoimmune hepatitis, a positive test result is not an absolute diagnostic criterion for this disease. Detection of anti-LKM in a patient without any other signs of liver damage is not interpreted in favor of the diagnosis of autoimmune hepatitis.
Such patients, however, require more careful observation by a doctor. On the other hand, a negative result of the study does not allow to completely exclude autoimmune hepatitis, in this case, a repeat anti-LKM study is recommended for a patient with clinical and biochemical signs of autoimmune hepatitis. The diagnosis of autoimmune hepatitis is made after excluding all other, more frequent, causes of hepatitis (viral hepatitis, toxic liver damage, congenital metabolic diseases).
Therefore, anti-LKM research is carried out simultaneously with laboratory diagnosis of hepatitis, research of liver function and some specific indicators (copper, alpha-1-antitrypsin).
The level of anti-LKM decreases when control of the disease is achieved, and the test may become negative. For this reason, it is advisable to perform repeated anti-LKM studies to assess disease activity. Autoimmune hepatitis is often associated with other autoimmune diseases, such as hemolytic and pernicious anemia and idiopathic thrombocytopenic purpura.
Therefore, with a positive result of the study and confirmation of the diagnosis of autoimmune hepatitis, additional studies are conducted to rule out concomitant diseases.