ANA are IgG antibodies against intracellular components of human cells. Both nuclear and cytoplasmic staining patterns are reported. Patient serum, diluted 1:40, is incubated with HEp2 cells and then fluorescent anti-IgG antibodies are added to detect any patient antibodies which have bound to HEp2 cells. For every new sample, if staining is seen the serum is titrated to determine the final titre. What is reported is the pattern and the titre (ie the dilution where the staining was still visible).
Examples of typical staining patterns can be seen in our fluorescence image library.
When should ANA be requested?
One of the problems with ANA is that up to 20% of the population have low/medium titre (i.e. 1:40 - 1:400), particularly in people over the age of 50 and also in children. Further more ANA also appear transiently following major or minor illness. The specificity of the test therefore reflects the clinical picture of the patient and are most useful in patients with suspected autoimmune disease.
What does a positive ANA mean?
Low titre ANAs (ie 1:40 or 1:100) are usually not clinically relevant whereas high titre ANA (particularly 1:1600) are infrequent amongst healthy individuals and so therefore carry a greater clinical significance. Below is a table of common ANA patterns and their clinical association. Possibly the most important use is to exclude SLE.