Sophie, I read about two measuring scales in Dr. Daniel Wallace's very helpful lupus hardcover. You could browse it in many libraries & bookstores.
1. ratios that keep doubling, e.g., 1:160 (read as "one to one-hundred and sixty"), 1:320, 1:640, 1:1280, etc. Dr. Wallace considers 1:1280 high.
2. the other is called International Units. Dr. Wallace considers anything over 30 I.U.'s high.
But ANA is elevated in various conditions, not just lupus (like RA, Sjogren's, scleroderma, Addison's, Hashimoto's thyroiditis, polymyositis, vitiligo); also due to family tendency, aging, or a passing virus. It doesn't mean that much in & of itself, except to encourage further study, probably.
Hope this helps some, best wishes, Vee