Fasting for a Blood Test
Sourced reference. This entry is compiled from MedlinePlus and is reproduced for reference rather than written by eMed7. Reference ranges differ between laboratories — always read a result against the range printed on your own report.
If your health care provider has told you to fast before a blood test, it means you should not eat or drink anything, except plain water, for several hours before your test. While you're fasting for a blood test, you should also not: Chew gum; Smoke; Exercise; Your provider will give you a copy of instructions to follow if they ask you to fast for a test. If you have any questions not covered in those instructions, ask your provider at least a full day before the test so that you'll have time to properly prepare.
Why this test is done
When you eat and drink, your bloodstream absorbs sugar, fat, protein, and other nutrients in those foods and beverages. These nutrients can then change the levels of various substances in your blood and therefore affect the accuracy of your test results. Inaccurate results give your provider an inaccurate view of your health and may lead to a wrong diagnosis.
Sample type
Blood
Full library entry
Reference ranges, sample type, and citations for this marker.
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- ncbi.nlm.nih.gov/pmc/articles/PMC7411170— MedlinePlus
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Educational content only. This entry describes what a test measures and how published reference ranges are defined. It is not a diagnosis, does not interpret your personal results, and is not a substitute for a qualified doctor.