Hi gavman.
Was it a urine test strip ?
If so, they reflect what was happening a couple of hours or more ago.
Keep testing and as long as it comes down to a safe level (ideally below 7 but don't let it overshoot and go hypo) he should be ok but needs to keep drinking water or sugar free drink to flush the system through.
Keep an eye out for nausea, headaches, stomach ache and feeling faint. If these occurr, he needs to get urgent medical attention, but I think the insulin should see him right.
If you're in doubt at all, dial NHS direct or, if you consider it an emergency, 999.
DKA is a serious condition but insulin in the system should sort it.🙂
Rob