Question: do you have to fast for a renal blood test?
Answer: Typically, people will be asked to fast for 10 to 12 hours before having one of these tests. Renal function panel: Tests to see how well the kidneys are working. Typically, people are asked to fast for 8 to 12 hours before these tests. Vitamin B12 test: Tests for the levels of the vitamin B12 in a person's blood.