Usually your BS/Bg levels being high is a sign of lack of insulin which causes DKA, But it's lack of insulin that causes DKA not actually just having high blood glucose. People can have very high Bg numbers and not have ketones because they still have enough insulin to stop it.
But it's ketones that tell you if you are at risk of DKA. Seek medical help right away if your ketones are too high, it's a risk we always have to be very careful of.