September 14, 2005
A1c (Glycohemoglobin, HgbA1c), Diagnosis and Symptoms
Question from New York, USA:
My primary care physician recently diagnosed me with type 2 diabetes based on only one fasting blood test and one A1c test. I had gone to see him in the morning for another matter for which he took a urine sample. He suspected diabetes because there was sugar in the urine and he asked if I had eaten that morning. Since I had not, he sent me for a fasting blood test. What I did not know at that time was that I was required to fast about 12 to 14 hours and I had not done so. Moreover, I had had a high sugar diet the previous night and had even eaten ice cream at midnight! In addition, I had received a very stressful call in the middle of the night. The fasting level was 205 mg/dl [11.4 mmol/L] and my A1c was 10.6%. Based on this, the doctor made the diagnosis of type 2 diabetes.
I have since read that one should confirm with a second fasting blood test and that an A1c is not necessarily used in the diagnosis. I insisted on a second blood test and, about nine days later, went for one after fasting the requisite number of hours. The results were actually normal, 98 mg/dl [5.4 mmol/L] although the A1c, though reduced, was down to 10.0%. The doctor stills maintains the diagnosis of diabetes. Is it possible for the fasting level to go from all the way up at 205 mg/dl [11.4 mmol/L] down to 98 mg/dl [5.4 mmol/L] in just nine days, with diet and exercise alone? Is there any other explanation for why the A1c could be high? The last three months have been very stressful indeed; could this be a reason?. Also, could alcohol intake play a role in an elevated A1c? Should I be following up with an oral glucose tolerance test or a two-hour postprandial test?
Answer:
In this case, I suspect that you could do additional fasting glucose levels, but you would have type 2 diabetes. The A1c is so high that it removes most of the doubt of the diagnosis. There has been some talk by experts in the field about trying to use the A1c to diagnose diabetes. It is not sensitive around the cutoff points. For instance, it lacks precision when the fasting glucose is around the 120 to 130 mg/dl [6.7 to 7.2 mmol/L] mark. However, when the A1c is 1% above normal, that is good evidence for diabetes. Your value is roughly 4% points above normal. You can have a 75g two-hour glucose tolerance test and that will settle the point. You can make your fasting glucose lower by cutting down on what you eat acutely. This may have had the effect of lowering your fasting blood sugar to such a degree. However, it is not likely you can sustain such a decrease in food intake to maintain that.
JTL
