Preparing for a blood test: fasting, water and other questions
Do you need to fast? Can you drink water or take your medicines? Here's how to prepare so your results are accurate.
Medisri Team9 October 2026 4 min read
Key takeaways
- Some tests need fasting, usually 8 to 12 hours. Your lab will tell you which ones.
- Plain water is usually fine while fasting and makes sample collection easier.
- Tell the lab about any medicines you take, and don't stop them without asking your doctor.
A little preparation helps make sure your blood test results reflect your health accurately, so you don't have to repeat the test.
Do I need to fast?
Some tests, such as fasting blood sugar, are affected by what you've eaten recently and need you to fast, usually for 8 to 12 hours. Many other tests don't need fasting at all. Your doctor or lab will tell you what applies to your test.
While you're fasting
- Plain water is usually allowed, and staying hydrated makes collection easier.
- Avoid tea, coffee, juice, chewing gum and smoking unless told otherwise.
- Book an early-morning slot, so most of the fasting happens while you sleep.
Medicines and supplements
Keep taking your regular medicines unless your doctor says otherwise. Tell the lab about any medicines or supplements you take, since some can affect certain results.
Wear a shirt with loose sleeves and keep your doctor's test request handy when the phlebotomist arrives.
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