The way the machine works, from what I hear ... is that they put the blood in and there are test cartriges that are in the machine.
The machine could handle exact same blood different each time. The machines also have a margin of error.
Fasting is not required. To do accurate tests, they would need to be hand verified (analyzed), or sent to a lab with more better, hi-grade equipment. Re-tests are needed to see if the levels are moving dramatically.
Since the other #'s are normal ... a re-test should ideally show more normal BUN level. I can't say this enough ... re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test, re-test.
http://www.dogaware.com/kidney.html