I wouldn't use a home meter to diagnose either prediabetes or diabetes. Firstly the meters are not accurate enough and are required only to be within a 20% range of the actual value and secondly, the quality of the blood sample by finger pricking is variable because you get other tissue fluids in the sample. Better is a venous sample, ie from a vein with a syringe and either, fasting blood levels over a period, ie from the blood plasma or better still a hba1c which gives a sort of 12 week average from the red blood cells. A single reading of 9 on a home meter really has no meaning. If you had them regularly, it's worth getting one of the other tests done.
Home meters are good as 'relative devices' ie they show you what foods do and do not work for you and with repeated testing show you if your average is going up or down. How true that average really is doesn't matter that much. I took my own fasting meter reading before I went for a venous test at the hospital. My result was 8.8 mmol/L. When I got back, I did it again and it was 8.0 mmol/L. The actual test at the hospital showed 7.6mmol/L.
All those weeks ago I got many readings in the 8s and 9s but they have come down slowly and now I am mostly in the 4s, 5s and 6s. Very occasionally, I get something in the 7s. I do watch what I eat however. I avoid sweets, buns, biscuits, chocolate bars etc but also white bread, white rice and mashed potatoes. I do however eat brown rice, wholemeal bread, wholegrain pasta and boiled new potatoes but am losing weight and doing exercise. So the drop in levels is through control, it hasn't disappeared.
But I did go for a walk on Morecambe promenade yesterday and treated myself to an ice cream. I remained in the 5s, but that's as much as I will push my luck for the time being.