Creatine supplements can be found at health food stores or you can eat red meat. This needs to be done 24-72 hours before the test. Some tests will test for creatinine clearance while some do not. It depends on the type of test and how much money the people who are testing you want to spend. What is your weight and height? A big, muscular person will naturally have a higher creatinine clearance than a skinny, little person.