I’m 63 and had gestational diabetes with my first pregnancy but not my second. I was put on a diet to reduce carbs and sugar as soon as I found out I was pregnant with the second. I’m pretty healthy, and work out with weights and some cardio almost daily. About 10 months ago I talked with my gynecologist about not being able to lose a few pounds, and she decided to check my A1C. It was 5.9. I have my fasting glucose checked every year, it’s always below 99, and this year it was 94. All my other blood test results are great. So what do I need to do? My PCP is waiting to check it again in a few months. I have been able to lose 6-7 pounds in the past 10 months by watching everything I eat. How are my A1C and glucose not matching up?
—Karen
I think you really have two questions here. First, why is your fasting blood sugar normal if your hemoglobin A1C is in the prediabetic range? And secondly, if your diet and exercise are already on point, what else can you do to keep from progressing from prediabetes to diabetes, or even reverse your prediabetes?
With regard to the first question, I think it helps to consider what each test actually is. Glucose is usually tested as part of a metabolic panel and is just a measurement of the actual glucose concentration in the blood at the time the test is performed. Fasting glucose just means you hadn’t eaten prior to the test. A normal result is less than 100 milligrams per deciliter, prediabetic is 100 to 125 mg/dl, and diabetic is a fasting glucose of 126 mg/dl or greater.
Hemoglobin A1C measures the percentage of red blood cells in the sample that have sugar molecules attached to the outside of the cell. This is directly correlated to the blood sugar over the life of red blood cells — in most cases about 90 days. A normal A1C is less than 5.7%; 5.7% to 6.4% is prediabetic; and 6.5% or above is indicative of diabetes.
Some people have impaired fasting glucose — that is, glucose that remains high with fasting. Some people have impaired glucose tolerance, which is high glucose after consuming carbohydrates. And some people have both. Because everyone is different, if a patient has risk factors for diabetes, I will typically check both fasting glucose and hemoglobin A1C annually. If your fasting blood sugar is in the normal range but your A1C is in the prediabetic range, this means that your blood sugars are rising proportionally higher after you eat than when you are fasting. A fasting blood sugar of 94 mg/dl and an A1C of 5.9% are not so discordant that I would be concerned.
The good news is that progression from prediabetes to diabetes is not inevitable. You have tools at your disposal that can help stave off progression. Improving your diet and optimizing your exercise routine are excellent first steps even if they do not result in weight loss. In one of my favorite papers regarding women with a history of gestational diabetes, researchers recruited women with a history of gestational diabetes and current dysglycemia — defined as impaired fasting glucose, impaired glucose tolerance, or prediabetes — and randomized them to usual care, intensive lifestyle change consisting of diet and exercise changes, or metformin.
Both the groups that followed intensive lifestyle change and those that received metformin were significantly less likely to develop diabetes. Unfortunately, the study did not have a group that received both intensive lifestyle change and metformin. However, I will often offer metformin as an option to my patients with prediabetes and a history of gestational diabetes.
The takeaway: Fasting glucose and hemoglobin A1C measure blood sugar in different ways, so it is not unusual for one to be normal and the other to be abnormal. Diet and exercise and metformin have both been shown to reduce your risk of progressing from prediabetes to diabetes.
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