ENA is extractable nuclear antigens.....
There are likely hundreds if not thousands of antibodies that can attack the nucleus of the cell. They have identified very few at this time, but the few they have found are, the rnp's, smith, SSA, SSB, scl 70, Jo and a few others I am too addled to think of.
When an ANA is +, it usually means the body is making autoantibodies against the nucleus....a part of the nucleus, usually the part that has something to do with replicating DNA, from what I can gather.
They looked at people with certain diseases and found that a % of them have these antibodies, so they test for them on all + ANAs. If you have a + ANA and negative ENA, it means they did not find these more common antibodies.....if you have them, it helps them identify your disease....you are fully seropositive so to speak.
If you have + ANA and negative ENA, diagnosis is a bit more problematic.....and this happens....so then they try to take a clue from the ANA pattern. Certain patterns are more common in certain diseases. Nucleolar is more common in Scleroderma or Polymyositis. Speckled or speckled/nucleolar is found more in SjS. Homogeneous in Lupus, anticentromere in Scleroderma.....however, none of this is written in stone....you can have any disease with any pattern.
Over 1:320 is almost never normal.....under than can occur in normal people.
These are clues, that is it, clues to what is going on with any one.
I hate doing taxes and I did not do well in math!!