If you need to fast for bloodwork, does it make a difference what chunk of time you fast for?

When I order fasting blood work, I tell my patients nothing but water for at least 10 hours.

That would be equivalent and satisfactory for most lab tests. Most of the time, nurses and staff that help patients prepare for such tests can guide you about how many hours ahead you you must fast so that the test results will be valid.

That would be fine. Only do drink plenty of water. My daughter didn’t and they had a hard time getting blood from her because she was dehydrated.

What happens with the results if the patient doesn’t fast?

Some tests don’t require fasting – thyroid function or CBC for example. The ones I order most often that do have to be fasting are diabetes screen aka fasting blood sugar and lipid profile total cholesterol, HDL, LDL, and triglycerides. FBS will be higher if you’ve been eating or drinking, and lipids will be thrown off too.

The time period for fasting before a blood test is 8 – 12 hours.

yeah, lipids is one of mine. Which really sucks, because I can’t sleep and I’m thirsty and my tap water is meh so unless I drive out to get bottled water, I suffer :P

The chunk of time should be immediately preceding the drawing of the blood. They usually say nothing after 11 PM.

Well first i always ask my nurse how much blood needs to get drawn so if its something small i usually say 12 pm but if its a lot i usually say either 9 or 10 pm