If your requisition says to fast, plain water is fine but coffee, tea, juice, food, gum and mints are not, for 8 to 12 hours before the draw. Fasting matters for glucose, lipid profile, iron studies and a few others; most tests, including CBC, TSH and A1C, need no fasting at all. Take your regular medications with water unless your provider says otherwise.
Can I drink coffee or water before a fasting blood test?
When you're asked to fast, plain water is not only allowed, it's encouraged. Staying hydrated makes it easier to draw your blood. What you should avoid during the fasting window are anything with calories or that can alter your results, including:
- Coffee, including black coffee, which can affect some test results
- Tea, including unsweetened tea
- Food of any kind, including snacks
- Chewing gum, including sugar-free gum
- Smoking
So the classic morning routine of coffee before bloodwork should wait until after your sample is collected. Bring your coffee with you and enjoy it on the way home. Even black coffee with no sugar or milk can influence certain results, so it's best to skip it entirely until you're done.
How long do I need to fast?
When fasting is required, it's typically 8 to 12 hours before your blood draw. For most people the easiest approach is to stop eating after dinner the night before, sleep through much of the fasting window, and come in first thing in the morning. Keep drinking water as usual. Always follow the specific instructions on your requisition or from your provider, since the required fasting time can vary by test.
Which blood tests need fasting?
Not every blood test requires fasting. Two important points:
- Fasting glucose does require fasting, typically 8 to 12 hours, to measure your blood sugar accurately.
- Routine cholesterol and lipid panels often no longer require fasting. Per Canadian guidance (CMAJ), many lipid panels can now be done without fasting.
Because practice varies, the golden rule is to follow your requisition: it will indicate whether fasting is required. If your requisition doesn't specify and you're unsure, call your provider or our staff before your visit rather than guessing. Fasting glucose is also commonly used, along with A1C, in diabetes screening; Diabetes Canada recommends screening adults 40 and older every three years, or sooner and more often with risk factors.
When should I schedule a fasting blood test?
If your test requires fasting, a morning visit is much more comfortable, since you can fast overnight instead of skipping meals during the day. At Bio-Test, mornings are our busiest time precisely because so many fasting patients come in early, so arrive prepared for a possible wait, or book ahead to plan your day.
Should I take my medications before a fasting blood test?
Fasting refers to food and drink, not usually your prescriptions. In general, take your regular medications as usual unless your provider has specifically told you otherwise. Some medications may need to be timed differently around bloodwork, so if you have any doubt, check with the provider who ordered the test before making changes. Never stop a prescribed medication on your own just because you're fasting.
How do I prepare and get my test at Bio-Test?
For a full checklist, see our guide on how to prepare for a blood test. When you're ready, most bloodwork at Bio-Test is walk-in, no appointment needed, and first-come, first-served, though mornings are busiest with fasting patients. Bring your Ontario health card and your requisition, which will confirm whether fasting was required. We have 11 locations across Ottawa-Carleton and Eastern Ontario; book online through our patient portal or just walk in, and home visits can be arranged by request for a fee.