Static - Whilst I'd be irritated by it, I wouldn't be overly concerned. It could be anything from not enough blood in the first sample, a peculiar reading, which they want to verify or clarify, the sample sat too long between collection and testing, making it unreliable at best, they lost the sample, so need to redo it to do it, to somebody dropped it and the vial smashed.
See what I mean?
Presumably you'll need to call to arrange the test or pick up the papers, so you could always ask for clarification then.
As NoCrbs4Me suggests, if you have access to your results, there could be some clues there.