When preparing for a blood test that requires fasting, the most common fasting period is 8-12 hours. This means not eating or drinking anything besides water for that period of time before having your blood drawn. While 10 hours falls within that typical range, there are a few things to consider to determine if 10 hours of fasting is enough for your specific blood tests.
What does fasting mean for a blood test?
Fasting for a blood test means not eating or drinking anything besides water. This includes:
- No food or snacks
- No coffee, tea, soft drinks, sports drinks, or juices
- No milk or dairy products
- No gum, mints, or candy
You can drink plain water during the fasting period. Some common blood tests that require fasting include:
- Lipid panel – Measures cholesterol and triglyceride levels
- Comprehensive metabolic panel – Measures blood sugar, electrolytes, kidney function, and more
- Hepatic function panel – Measures liver enzymes
- Complete blood count (CBC) – Measures blood cells and hematocrit
Fasting causes your blood sugar and fat levels to stabilize, giving the most accurate results for these tests. Fasting recommendations vary slightly depending on the specific blood test.
Is 10 hours of fasting enough?
For most standard blood tests that require fasting, such as a lipid panel or metabolic panel, 10 hours is typically enough. However, some recommendations suggest a longer fast:
- Lipid panel – 12 hours
- Glucose tests – 8 to 12 hours
- CBC – 8 hours
When in doubt, it’s best to fast for 12 hours to ensure your blood draw gives the most accurate results. For example, if your appointment is at 8am, stop eating and drinking (besides water) the night before by 8pm.
Who may need a longer fast?
Certain individuals may be advised to fast for longer than 10 hours before blood tests, such as:
- People with diabetes – A 12-14 hour fast may give the most accurate blood sugar results.
- Pregnant women – Blood sugar and lipid levels can remain elevated longer. A 12-14 hour fast is often recommended.
- People taking certain medications – Medications that affect glucose and lipid metabolism may require longer fasts for accurate results.
It’s best to follow your healthcare provider’s advice on proper fasting times if you fall into one of these categories.
Tips for successful fasting
Here are some tips to help make fasting easier and ensure accurate blood test results:
- Stay well hydrated – Drink plenty of water during your fast.
- Avoid strenuous exercise – Take it easy to prevent low blood sugar.
- Schedule blood draw early – First thing in the morning is ideal after fasting overnight.
- Set a reminder – Make a note of when to start and end your fast.
- Avoid smoking – Don’t smoke for at least an hour before your test.
What if I break my fast early?
If you unintentionally eat or drink something other than water during your fast, here’s what you should do:
- Note what time you broke your fast and with what food/drink.
- Continue fasting until your appointment.
- Notify your phlebotomist when you arrive that you accidentally broke your fast early.
Breaking your fast more than an hour before testing could impact results. Your doctor may recommend rescheduling the test if you ate a significant amount and did not fast the full time.
Summary
In summary, 10 hours of fasting is generally enough time to get accurate blood test results. However, a 12-14 hour fast is ideal and recommended for most blood tests that require fasting. Some people, such as those with diabetes or taking certain medications, should fast for longer periods before blood testing. Be sure to follow your healthcare provider’s instructions for fasting to get the most accurate blood test results.
Frequently Asked Questions
What can I have during a fasting blood test?
The only thing you can have during a fasting blood test is plain water. Do not consume any food, drinks other than water, gum, mints, or candy.
What blood tests require fasting?
Common blood tests that require fasting include:
- Lipid panel
- Glucose tests
- Liver function tests
- Kidney function tests
- Complete blood count (CBC)
How long do I need to fast for a blood sugar test?
For a fasting blood glucose or hemoglobin A1C test, an 8 to 12 hour fast is typically recommended. Some doctors advise 12 to 14 hours of fasting for the most accurate blood sugar results.
Can I drink coffee before a fasting blood test?
No, you cannot drink coffee before a fasting blood test. Coffee, tea, juice, soda, and other drinks besides plain water are not allowed during a fasting period. The only liquid permitted is regular water.
What if I forget and eat before a fasting blood test?
If you accidentally eat or drink something before a fasting blood test, note the time and what you consumed. Notify the phlebotomist when you arrive for your test that you broke your fast early. Your doctor may recommend rescheduling the test depending on how early you broke the fast.
Sample Fasting Instructions Table
| Blood Test | Recommended Fasting Time | What’s Allowed |
|---|---|---|
| Lipid Panel | 12 hours | Water only |
| Glucose Test | 8-12 hours | Water only |
| Liver Function | 12 hours | Water only |