American Association for Clinical Chemistry
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NACB - Scientific Shorts
NACB - Scientific Shorts (formerly NACB Blog)
By William E. Winter, MD, and Roger L. Bertholf, PhD

The title of this NACBLOG post is a question that was recently posted on the AACC chemistry list serv. Does Circadian Rhythm Impact Fasting Blood Glucose Testing?

What is your response? Check back for our response on Monday, April 30, 2012.

Yes, circadian rhythm does impact fasting plasma glucose levels.

In an article published in 2000 (JAMA 284:3157, 2000), the frequency of hyperglycemia (glucose =>126 mg/dL) in the study populations was higher when drawn after an overnight fast (2.8%) than when drawn as a fasting afternoon sample (1.4%).

Therefore if a fasting plasma glucose measurement is used to screen for diabetes, an overnight fast is preferred to sampling in the afternoon. In the quoted study, the subjects drawn in the AM had fasted for a mean of 13.5 hrs and the subjects drawn in the afternoon had fasted for a mean of 7 hours.




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Posted by William Winter
On 5/10/2012

We posted this question because sometimes clinicians request that the lab measure a fasting plasma glucose in the afternoon or perform an OGTT in the afternoon. Certainly we can do this but such testing is less sensitive than AM testing. If you're old enough (like me), you might remember when researchers would do a cortisol-primed OGTT to try to elicit hyperglycemia.

Posted by William Winter
On 5/10/2012

Cortisol's actions are to increase the expression of gluconeogenic enzymes and produce peripheral insulin resistance to raise blood glucose concentrations.

Posted by Ola Sharaki
On 5/5/2012

I think circadian rhythm impacts FBG testing since cortisol hormone which is an important hormone that has an influence on glucose metabolism shows a a diurnal variation reaching in the evening half the value of the morning.

Posted by Krystyna Sztefko
On 5/4/2012

Yes! It always takes time to keep our body in discrete metabolic balance.

Posted by Ioannis Papageorgiou
On 5/4/2012