What Happens if You Don’t Fast Before a Blood Test?

You may have to fast before having some blood tests. You will be notified by your doctor beforehand whether you can eat or drink anything. Sometimes, you are asked not to consume anything, except water several hours before the test.

It is very vital to fast before some blood tests to ensure the accuracy of test results. All the food and beverages have minerals, vitamins, carbohydrates, fats and proteins which affect readings of your blood sugar level and results are clouded. You don’t have to fast beforehand for all blood tests. But here are some tests which require you to do so –

  • Liver function test
  • Blood glucose test
  • Triglyceride level test
  • Cholesterol test
  • Renal function panel
  • Lipoprotein panel
  • Basic metabolic panel
  • LDL level test
  • HDL level test

If you are prescribed with a new blood test and you don’t know whether fasting is necessary, you should ask them first. Fasting is not required in some blood tests like fecal occult tests but you cannot eat some foods. Some medications, broccoli, and red meats also lead to false positives. So, ask your doctor for advice before going for a test.

Can you still go for a blood test without fasting?

As discussed above, your test results may not be technically correct if you avoid fasting before having a blood test. If you drink or eat something by mistake, ask your doctor if you can still go for the test. The technicians at the best pathology lab in Gurugram will analyze the test considering that you were not fasting.

Of course the results will vary. The key here is to be direct. Even if you had some coffee before having a test, inform the technician before getting your blood drawn. They will write it down and review the results with a variable of food intake. However, they can reschedule your blood test if fasting is the #1 priority for accurate results.


Even better, you can drink enough water in two days leading up to your test because your veins will be more visible as water hydrates the body. You may drink several glasses of water before they draw your blood so a nurse or other professional can easily find a vein.