- ANA stands for "Antinuclear antibodies".
- Antibodies are proteins produced by white blood cells, which normally circulate in the blood to defend against foreign invaders, such as bacteria, viruses, and toxins.
- The antibodies that target “normal” proteins within the nucleus of a cell are called antinuclear antibodies (ANA). 
- Most people have antinuclear antibodies, but typically in small amounts. The presence of large amount of autoantibodies or ANAs can indicate an autoimmune disease.
- A negative ANA reading means no antinuclear antibodies are present in the body. 
- A positive ANA reading alone does not indicate an autoimmune disease.

-------------------------

The ANA titer is a measure of the amount of ANA in the blood; the higher the titer, the more autoantibodies are present in the sample.

Patient samples are often screened for antinuclear antibodies after being diluted 1:40 and 1:160 in a buffered solution. If staining is observed at both the 1:40 and 1:160 dilutions, then the laboratory continues to dilute the sample until staining can no longer be seen under the microscope. The level to which a patient's sample can be diluted and still produce recognizable staining is known as the ANA "titer." 

Here is an example:

Serial Dilutions:
1:10 positive
1:20 positive
1:40 positive
1:80 positive
1:160 positive (titer reported as 1:160)
1:320 negative

Resources:

- https://www.lupus.org/resources/common-symptoms-of-lupus
- https://www.uptodate.com/contents/antinuclear-antibodies-ana-beyond-the-basics