Common tests in autoimmunity: The antinuclear antibody (ANA) test
By Adrian Lee
One of the most commonly ordered tests when a doctor suspects an ongoing autoimmune process is the antinuclear antibody (ANA) test. This is a test on the serum of blood (the non-cellular component without clotting factors) that takes a couple of days to perform. The ANA test examines for the presence of ‘self’ antibodies (immune system proteins which bind other proteins to initiate an immune response) against nuclear components of human cells. Because there are many proteins in the nucleus, the ANA test is actually looking at a hetrerogeneous group of antibodies.
There are two components of the ANA test that are typically reported: (1) the degree of positivity; and (2) the staining pattern of the test. When an ANA test is reported as positive, the degree of positivity will be reported as a titre – this is a dilution of patient serum that will give a positive result. The higher the concentration and reactivity of antibodies, the more dilute a patient serum can be to be positive. Because the antibodies have different targets, they can stain in different patterns when examined under a microscope. Distinct patterns have been identified which are associated with certain diseases.
What does a positive mean?
The simple answer is: not a lot. Positive results need to be interpreted by a qualified professional in clinical context (after careful history-taking and examination) and often additional investigations. Unless the result suggests an ‘extremely positive’ ANA, the suggestion that there is an autoimmune process is not very well supported. A few other medical conditions can also give a positive result even in the absence of autoimmunity; this is why careful interpretation is needed.
ANA is a general test that is ordered when immunity is suspected. A large number of autoimmune diseases are positive for ANA; but the bottom line is that it can also be negative in these diseases and ultimately, the result needs to be considered in clinical context.
Lee AYS, Ang EBH. A clinical overview of antibodies in general practice rheumatology. Br J Gen Pract. 2014; 64(626): 485-6.
This article is provided for general education and information only and should not be a substitute for a qualified healthcare professional’s nterpretation and/or advice on pathology tests; medical treatment; or medical care. Consult your doctor or healthcare professional if you have any concerns.
Adrian Lee, B.Med.Sc(hons.)
Adrian is a medical student at the University of Tasmania with strong clinical research interests in autoimmunity. Thank you Adrian for this article it explains what ANA test entails. I have often wondered what the test meant and you have explained it clearly for me . Ed.