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Quality Health Care and You - Diabetes

Information on Normal Readings

05/22/2008

Question:

I have not been diagnosed with diabetes, but my doctor is asking me to check my glucose level because of a hemoglobin A1C reading of 6.4. She wants the A1C reading under 6.0. One hour after a meal, my reading may go to 179. My fasting is consistently 90 to 102 but mostly in the low 90s. In a non-diabetic, how high can a reading after a meal go and the person still not be considered diabetic?

Answer:

When assessing blood glucose levels, there are three categories: 

"Fasting" is defined as no caloric intake for at least 8 hours. "Casual" is defined as any time of day regardless of time since the last meal or snack. 

Normal: 1) Fasting blood glucose less than 100 mg/dl, 2) Casual blood glucose less than 140 mg/dl.

Abnormal glucose tolerance but not diabetes: 1) Fasting blood glucose greater than or equal to 100 but less than 126 mg/dl, 2) Casual blood glucose greater than or equal to 140 but less than 200 mg/dl.

Diabetes: 1) Fasting blood glucose greater than or equal to 126 mg/dl, 2) Casual blood glucose greater than or equal to 200 mg/dl with classic symptoms of diabetes (urinating frequently, more thirsty than usual, unexplained weight loss). One of the criteria should be present on two separate days, in the absence of obvious high blood glucose levels.

These categories are based on a blood sample drawn from the vein and sent to a clinical laboratory.  They are not meant to be applied to finger stick blood glucose determinations which give slightly different results and are not as accurate.

Hemoglobin A1c is a long term test of average blood sugar control.  Values are compared to the normal range identified by each laboratory. If the A1c test result is above the normal range, it indicates the average blood glucose levels for the past 2-3 months have been higher than normal. A1c test results reflect an average of blood glucose levels every minute of the day, for the past 2-3 months.  Currently, the American Diabetes Association does not recommend making a diagnosis of diabetes based on HbA1c, in particular compared to the laboratory normal range.  However, an abnormal HbA1c may be a reason to do the more specific glucose tests. 

There was one important study (Peters and coworkers, Journal of the American Medical Association 1996) which recommended using HbA1c with a higher cutoff than the upper limit of normal as a basis for saying that the person has "diabetes requiring treatment."  I tend to use that criterion quite a bit.  That cutoff will vary from one lab to another but will generally be about 0.5-0.6 above the upper limit of normal for their HbA1c measurement.

For more information:

Go to the Quality Health Care and You - Diabetes health topic, where you can:

Response by:

Nancy J Morwessel, CNP, MSN, CDE Nancy J Morwessel, CNP, MSN, CDE
Pediatric Nurse Practitioner
Diabetes Center
College of Medicine
University of Cincinnati