How does the HbA1c test screen for diabetes or pre-diabetes?

[TheDaughterInLaw]

My understanding is that the HbA1c result reflects what a person's average glucose has been over time.  If a result such as 5.8% translates into an "average daily" value of 120 mg/dL, how can 5.8% be considered normal?  Is it because your blood glucose varies over the course of the day, making 120 mg/dL a high value for a fasting glucose level but not necessarily high when a whole day's variation is taken into account?

[TheDaughterInLaw]

I worked in medical labs for years and it was quite typical to see glucose values over 100 when patients were given a glucose tolerance test.  The normal values in our lab at that time were 80-120 mg/dL, but fasting glucose levels over 100 mg/dL typically resulted in follow-up testing for the patient.

The section of the lab I worked (Clinical Chemistry) didn't do the HbA1c test.  It might've been done in a different section or it may not have been available yet back then.

When my husband had the test done last week, it came back with a value of 5.8% - which the nurse told him was normal.  He handed the phone to me to ask more questions, so I asked what that translated to in terms of his glucose level and she told me it reflected an a daily average value of 120 mg/dL.  Of course, to me, that did not sound "normal."  That's why my question was about the apparent conflict.

He has another appointment in a couple weeks but, of course, I was too curious (and concerned) to wait that long to ask his doctor what's going on.  It's probably better that I do, though, because he certainly didn't appreciate me suggesting he cut back his sugar intake after the nurse told him his result was "normal!"

I really do appreciate your insight, Super_sally888.  Thanks.

[Super_sally888]

A person who is not diabetic would rarely if ever have blood sugar over 100.

Most people with completely normal blood sugar would usually be in the 80s (average about 83) and would stay there regardless of what they eat.

If you are diabetic, it is of course optimal to get your numbers to or as close to normal as possible - without going low or high.

Hope this helps.

[WaveRider]

"When you say postprandial levels should be <141 mg/dL for diabetics and optimum <121 mg/dL, do you mean <121 mg/dL is optimum for diabetics?"
Yes. Lower is even better but extremely difficult to obtain for t2 diabetics.

"Or do you mean it would be a normal daily average value for anyone?"
No, these levels do not apply to "anyone", only t2 diabetics. Also, omit the word 'daily' as it does not apply when speaking of postprandial.

[TheDaughterInLaw]

When you say postprandial levels should be <141 mg/dL for diabetics and optimum <121 mg/dL, do you mean <121 mg/dL is optimum for diabetics?  Or do you mean it would be a normal daily average value for anyone?

Thanks!

[Super_sally888]

Truely normal A1C is less than 5.0.

An A1C of 5.8 (average somewehre around 120) is higher than truely nromal and should be telling you to make lifestyle and diet changes and keep monitoring things closly.

This could reflect lower fastings and higher after eating... or it could reflect generally raised levels.

If you can get a test kit you coudl try testing fasting levels upon waking (ideally < 95, truely normal in the 80s.), and 2 hours after eating which should be < 120 and ideally close to your fasting levels.