Dear Center for Phlebotomy Education:

Providers in our clinics have approved an 8-hour fast as sufficient for glucose, lipids and Hemoglobin A1C. I've always heard a 12-hour fast is optimal. Also, the question has come up about whether we should inquire the fasting status of every patient we draw for panels that include glucose or lipids even if they weren't ordered as fasting panels. That seems excessive to me. What should we do?

My Response:

Generally, a fast is defined as a 10- to 12-hour dietary restriction of everything except water and medications. For lipids, a daytime fast is considered acceptable but for glucose it must be overnight.

Some facilities strictly enforce a 12-hour fast for lipids while others relax it to 8-12 hours. However, over the last several years there have been discussions in cardiovascular circles as to whether fasting for lipids is even necessary. So the waters are getting kind of murky right now. Until science sorts things out, your medical staff should establish the parameters they feel most comfortable with. 

For diabetes testing, however, most facilities consider a 10-12 hour overnight fast to be optimal. It would not be unacceptable for your facility to establish an 8-hour fasting policy. One study, published in 2011, suggested a 3-hour fast would be acceptable for glucose. Since it must be an overnight fast, though, and since most people sleep 8 hours, an 8- to 10-hour fast should not be too burdensome to impose.

I like the idea of documenting every patient's fasting status when lipids or glucoses are ordered. Though it's not required by the standards, the more information the physician has the better he/she can interpret the results.