Blood and lab tests
What Is a Fasting Blood Sample?
Fasting Sample · say it: FAST-ing SAM-pulAlso written: fasting blood test, fasting specimen, fasted, non-fasting
Short answer
A fasting sample is blood taken after you have had nothing to eat or drink except water for a set number of hours.
What it means
Some test results change after a meal, especially blood sugar and triglycerides. To get a consistent baseline, a clinic may ask you not to eat or drink anything except water for a set time before the test, often overnight.
Reports sometimes note whether a sample was fasting or non-fasting, because the lab or doctor may interpret the result differently. Many cholesterol tests no longer require fasting, but some still do.
Follow the instructions given by your own clinic, including what to do about any regular medicines, and tell the person taking your blood if you did not manage to fast.
Where you may see it
- Blood sugar (glucose) tests
- Lipid or cholesterol panels
- Some hormone and metabolic tests
📄 How it looks on a report
Glucose, fasting 5.4 mmol/L
🙅 What it does not mean
- Fasting usually still allows water; it does not normally mean avoiding all fluids.
- A non-fasting result is not wrong, but it may need to be read differently or repeated.
- Fasting does not automatically mean stopping your medicines; ask your clinic first.
🗒️ Questions to ask your doctor
🧾 Reports where you will see “Fasting Sample”
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🔗 Read more from trusted sources
- “Fasting Sample” on MedlinePlus ↗
US National Library of Medicine
- MedlinePlus lab test guides ↗
US National Library of Medicine
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More words: blood and lab tests
General information about a medical word, not advice about your own results. Ask the clinician who ordered the test what it means for you.