Do you really need to fast before that blood test?

You were told to fast before your blood test, but your appointment isn’t until 3 pm and you are starving.  Will it really make a difference?

For some tests, yes it actually will.

Fasting for a blood glucose test is important, because this test can help diagnose diabetes.  It is important that a patient has not had anything to eat or drink for 8-10 hours before the test, to ensure an accurate blood glucose level test to rule out diabetes.

Fasting is also important for cholesterol testing.  Cholesterol is a type of fat in our blood.  If a patient has eaten a meal before the test, the results will be skewed.  It is important not to eat for 8-10 hours before this test as well.

Not fasting before a blood test can also affect blood iron testing to evaluate for anemia.

Fun fact:  Smoking or drinking alcohol before a blood test can cause liver function tests to be abnormal.  It is best not to smoke or drink alcohol for 24 hors before liver function testing.