in other words, >1:1280 means you have as high of an ANA as they expect to ever see.
I hate to be pedantic, but it is definitely quite possible to have an ANA that is higher than 1:1280 - I myself have had ANA's 1:2580, and have heard of people having ANA's in the 5,000's. Actually, I myself have never heard before of a lab that stops titrating at 1:1280, but it seems that this particular lab does.
My thinking would be that they don't think it is worth the expense of continuing to tirate beyond 1280, as increased levels don't mean increased sickness, so it is not medically relivant to know what the highest level a person would test out at. an ANA of 1:1280 is a good strong positive, so nothing is achieved by continuing to titrate.
Titres double each time - 40, 80, 160, 320, 640, 1280 etc so numbers get large very quickly.
I have had lupus since I was 12, so I have been tested on this scale for many many years. Also, there is a newer way of testing ANA's that gives a single number and a vastly different scale than the old ratio's.
Titres like 1:80 and even 1:160 are pretty much ignored by rheumie's, as they often occur in healthy populations who do not have associated disease. These false positives increase with age. Rheumies usually like to see an ANA of at least 1:320 to dx unless there are compelling symptoms or other antibodies that support a dx.
The ANA is a screening test and if positive further testing is done. The most specific thing for lupus is the anti-ds-dna antibody, and if present it pretty much clinches the diagnosis of lupus. Over 95% of people with lupus have a positive ANA, but most people who have a positive ANA don't have lupus, if you get my drift, as lupus is only one of a variety of possibilities if a person has a positive ANA.
Ok, that's my take on this stuff having been around the block a few times with antibody tests ..... my dx with lupus was made very easy by high levels of both ANA's and anti-ds-dna's, althought I have lots of other antibodies as well.