How does eating skew a blood test?

[graylocks]

Robert M wrote:
The sugar contained in the banana could skew the amount of sugar that is in your son's blood when he takes the test. It could take X amount of time before the sugar levels go back to what they are normally.

Robert

working with my limited medical/chemical knowledge here - so the banana most likely elevated his glucose level which his doctor read normal. does a higher than standard glucose reading indicate a pre-diabetic state or does a lower than standard glucose reading indicate a pre-diabetic state?

i'm also trying to google this but not hitting results i can easily understand.