First, you’ll need a physician’s written order for your specific test(s). If you’re being tested for glucose or lipids, you will need to fast for 10 to 14 hours before the test. This means drinking only water as well as avoiding juices, caffeinated drinks, nicotine and even chewing gum. Other tests may also require fasting. If you’re uncertain if you should fast before your test, contact your physician or the YRMC Laboratory you’re planning to visit.