There is a difference in how some meters report blood sugar readings which depends on whether the meter measures whole blood glucose or plasma. From what I've read online, most home meters measure whole blood and labs measure serum/plasma, which normally come out several points higher than the home meters. I'm not sure what this means if your home meter agrees with the lab results since there's an allowance of 20% higher or lower for meters' accuracy.
I have an old Bayer Contour (takes 15 seconds) that consistently measures higher than my newer ones (5 seconds). I no longer have the original manual for the older model, but the newer one says it measures in whole blood. However, it also says the meter, "...has been referenced to plasma/serum values. Methods calibrated to plasma/serum can be 9 to 15% higher than the results of whole blood glucose assay methods." I'm sorry but I don't understand this: does this mean the reading I see is whole blood or serum? (Yes, I called Bayer and that's another frustrating story.. 
)
This sort of explains the difference:
http://www.ehow.com/facts_6088215_difference-blood-glucose-plasma-glucose.html