It's (I think, I'm not an expert) impossible to say for sure if I was dehydrated or not. However, it does give me reason for the next time I get tested to make 100% sure that I am not dehyrated. BUN and Hematocrit values have been shown to be higher in individuals who are dehydrated.

Correct me if I'm wrong, but I think some professional cyclists have even blamed a high hematocrit result on dehydration.