What to do if you eat before a blood test that requires fasting?

Posted By Suborna Fermi Posted on Jun 29, 2025

We are always surrounded by harmful pollutants and deadly viruses, hence, falling sick is natural. This is exactly why blood tests are no less than lifesavers these days. As we all know, blood tests can help the medical professionals detect hidden diseases, even during their primary stages, which makes it easier for us to seek medical attention on time. There are so many types of blood tests that are available widely, and some of those require overnight fasting.

Which blood tests usually require fasting?

Blood tests that demand fasting include

• Blood cholesterol test: Up to 14 hours of fasting can be required.
• Blood glucose test: 8-10 hours of fasting can be required.
• Serum iron test: 12 hours of fasting can be required.
• Triglyceride levels test: Sometimes a 12 hours of fasting is suggested.
• Renal function panel: 8-12 hours of fasting can be required.
• Vitamin B12 test: Rarely, 6-8 hours of fasting is suggested.
• Vitamin B complex test: overnight fasting can be required.
• Gamma-glutamyl transferase test: Overnight fasting and no alcohol intake for 24 hours is recommended.

What to do if you eat before a test that demands fasting?

Now the question is, what to do if you have mistakenly consumed any food before any test that requires fasting? The first thing to do is to inform the healthcare providers what you have eaten and in what amount during your hours of fasting. Only the pathology lab experts can decide whether the test can still be performed or not.

However, there remains a chance of receiving faulty test reports if you eat before a test that demands fasting. When you eat something, the nutrients from those foods impact the levels of minerals in your blood, making it almost impossible for the test to get the accurate count of minerals and find underlying abnormalities and imbalances. Hence, you may consider taking the test another day if you mistakenly broke your fast.

Effective tips for uninterrupted fasting before a blood test

• Eat enough before the fasting period starts.
• Drink water to cope with your body’s craving for food.
• Schedule a morning test, so that skipping meals only one time can be enough.
• Avoid any kind of heavy activity during the fasting hours.
• Keeping your mind distracted somehow may help you cope with hunger.

Once again, try not to intake anything before any test where fasting is needed. You may consult pathology lab experts to know more in this regard.