The accuracy of a number of test results directly depends on what you do before giving a sample. The best-known example is a glucose (blood sugar) test and the food/drink consumed before taking the test. If you eat sugar-containing food and drink sweet drinks (such as sweetened coffee or tea) before giving a blood sample, it will raise the blood glucose level and the test result will not be accurate. Therefore, please regard sampling guidelines seriously – if you follow the guidelines, the lab can give you test results that are as accurate as possible.