Blood test for sugar levels question

[booox]

Hi, I've been having various issues for a while and often get my 'blood sugars' (I know no more than this) done while checking other things.

I didn't know it was going to be done this morning, but it occurred to me that perhaps I shouldn't be eating before the test?

Or is it just a screen thing they do anyway?

I think I had a different diabetes marker done a coupe of years ago which was really good so I don't think it's an issue, however one of the issues has been weight loss or not really gaining and fatigue hence checking that, plus I have hypothyroidism so could be linked 'autoimmunely'.