I was diagnosed with type II diabetes based on a 3 hour glucose tolerance test (GTT) with an abnormal 2 hour glucose level of 202, while on Glucophage. About a week later, a hemoglobin A1c test was done which was normal (5.3 percent). The doctor indicated that I could stop the Glucophage, which I did but I am still worried about this. How is it possible that the 2 hour GTT was abnormal and the hemoglobin A1c test, normal? I was also on a 2000 calorie American Diabetes Association (ADA) diet.
You raise some very interesting points both about the diagnosis of diabetes, and the monitoring of the condition once it has been diagnosed.
The American Diabetes Association revised the diagnostic standards for diabetes. The standard is slightly different for type I and type II diabetes and I will discuss only the type II standard, since that is what you have, if indeed you are diabetic. Type II diabetes should be diagnosed if the fasting plasma glucose is greater than 126mg/dl on more than one occasion, or if the 2 hour plasma glucose following a glucose tolerance test (GTT) is greater than 200mg/dl. Therefore, by strict criteria you have type II diabetes, since your 2 hour glucose level was 202.
An intermediate condition, impaired glucose tolerance is also recognized, and is defined as a 2 hour value between 140 and 200mg/dl on the GTT. About 35 percent of people with impaired glucose tolerance will eventually develop frank diabetes.
Your doctor appropriately tested your hemoglobin A1c level. This test, which measures the percentage of hemoglobin A molecules which have had a glucose molecule attached to them and are said to be glycosolated, has greatly improved our ability to manage diabetes. Surprisingly, your A1c level was normal. But how could that be, if you were an untreated diabetic until 1 week prior to having the test? I can see two possible explanations: one — that you are not truly diabetic but only have impaired glucose tolerance, and the single GTT value was an anomaly, or lab error; or two — that you have become diabetic so recently that you have not had time to build up your A1c result to an abnormal level. Since the A1c test reflects the average glucose level 24 hours per day during the previous two months, if your average level has been high for only a couple of weeks, the A1c test may not yet be abnormal.
Although these diagnostic issues are interesting, many doctors, including myself, would say that whether or not you have diabetes is less important than the fact that you have a normal A1c level. One theory about the cause of the dreaded complications of diabetes, the kidney failure, retinopathy, and neuropathy is that they develop because of excessive glycosolation of proteins in those organs as a result of the high average glucose levels usually seen in this disease. If this is the case, and you keep your A1c level in the normal range, then you will not be at any greater risk of these complications than the non-diabetic population.
So I would agree with your doctor’s decision to stop the Glucophage — a wonderful drug for diabetes, by the way — until you see if the A1c level stays normal over time. Checking it every three to six months should be often enough, since it changes so slowly. If it creeps up and passes the normal level of 6.5 percent (the normal level may be different in different labs), then a stricter diet and perhaps medication may become necessary.
In the meantime, you should certainly take your GTT results as a warning. If you are overweight, as are 90 percent of type II diabetics, then weight-loss will be very important. Diet and exercise are crucial to controlling the sugar as well as for losing weight. Type II diabetics who lose substantial weight can become non-diabetic, at least according to our tests, and greatly reduce their risks of those complications. This requires a major, permanent change in eating habits and lifestyle which unfortunately many people are unable to achieve, but for those who do, the benefit is enormous.