Antinuclear antibodies (ANA) are commonly found in autoimmune diseases. Positive ANA is not a diagnosis of autoimmune disease, but it is often found in diseases such as systemic lupus erythematosus (SLE), systemic sclerosis, Sjogren's disease, polymyositis and rheumatoid arthritis. Approximately 90% of patients with SLE are ANA positive in the course of disease.
Who and where ANA is done is very important. Many experienced rheumatologists will have an office lab that is skilled in conducting ANA testing properly. In many cases, commercial laboratories have staff who are not skilled in the interpretation of ANA.
ANA is a very sensitive screening test for the diagnosis of SLE. However, on the other hand, especially when ANA is low level, it is associated with many false positive test results. Typically, ANA levels below 1: 80 are less important than higher levels. However, the interpretation of ANA must be done in combination with the patient 's medical history, physical examination and other information to make appropriate diagnosis.
ANA also has a pattern. These patterns sometimes refer to diagnosis, but are usually not specific. One pattern that appears to be certainly specific is the anticentromere pattern seen in conditions such as systemic sclerosis or limited skin sclerosis. The pattern of nucleolus is associated with Raynaud's syndrome and systemic sclerosis. Other patterns such as diffuse or speckled are less specific. In rare cases, edges or peripheral patterns may be seen in SLE patients.
If the patient has positive ANA and other clinical signs, a more specific laboratory examination is required. Testing of these more specific antigens (proteins) is usually carried out using the so-called ELISA technique. Antibodies to double-stranded DNA are specific for SLE as 70% of patients with SLE have antibodies against double-stranded DNA at some point in the disease. High levels of antibodies to double-stranded DNA are more severe diseases and indicate a high likelihood of kidney disease. Measurement of antibodies against double-stranded DNA changes with disease activity and this measurement should be delayed for monitoring purposes.
Anti-Sm antibody (anti-Smith) is also specific for SLE but exists only in about 30% of patients with this disease. RNP antibodies are found in patients with conditions known as mixed connective tissue disease (MCTD).
Antibodies against SSA and SSB (also known as Ro and La) can be seen with primary Sjogren's disease and SLE.
Other useful tests are anti-histone antibodies found in drug-induced lupus, anti-Scl-70 found in systemic sclerosis, and anti-Jo-1 seen in dermatomyositis.
Repeating these tests for monitoring purposes is often useful when these specific antibodies are performed as a quantitative means, meaning that a number representing the amount of antibody is given.
The place where these more specific tests are done is again important. When conducted by an experienced laboratory conducted by an experienced technician, the reliability is much higher than if it is carried out in a typical commercial laboratory. In the commercial laboratory, a huge amount is being handled, and incorrect results may be obtained by mixing with the specimen.
