Some blood tests read what you have eaten in the last few hours as much as your health. For those, an empty stomach is what makes the result accurate. Your booking tells you whether a test needs fasting, and for how long.
Which tests need fasting?
Mainly the ones that measure sugar and fats in your blood:
- Fasting blood sugar (glucose): at least 8 hours without food.
- Lipid profile (cholesterol and triglycerides): 10 to 12 hours without food.
- HbA1c needs no fasting. It shows your average sugar over the last two to three months, so a meal does not change it.
What you can and cannot have
- Plain water is fine, and helps: a well-hydrated vein is easier to draw from.
- No tea, coffee, milk, juice, soft drinks or chewing gum while you fast.
- Avoid alcohol for 24 hours before the test, and heavy exercise the evening before.
Your medicines
Keep taking your regular medicines unless your doctor tells you otherwise. If you take medicine for diabetes, ask your doctor whether to take the morning dose before your sample is drawn or after it, as fasting with that dose can lower your sugar too far.
Making it easy
- Book an early-morning home collection, so most of the fast happens while you sleep.
- Have breakfast as soon as the sample is taken, and carry a snack if you have diabetes.
- Tell the phlebotomist if you could not fast, rather than skipping the test: some results can still be read with that in mind.
