The Extractable Nuclear Antigens (ENA - 18) test is a laboratory test designed to detect antibodies against a group of nuclear antigens associated with autoimmune diseases. This test includes 18 types of antigens, providing a detailed assessment of the immune system's status. ENA - 18 is commonly used in the diagnosis of diseases such as lupus erythematosus, rheumatoid arthritis, and other related conditions. By identifying the presence of these antibodies, the test helps doctors understand the nature of the disease and guide appropriate treatment for patients.