Creatinine confusion

Went down to my GP's this morning for a follow-up creatinine test to make sure my kidney is functioning properly. I was convinced this was a urine test, so in an effort to repeat the embarrassment I went through at the hospital the other week when it took me ages to provide a sample, I drank several glasses of water over the course of the morning to the point where I was busting to go. When I got to the doctor's the nurse informed me it was a blood test.