Fasting Blood Sugar

Last week we discussed the use of the random blood sugar in monitoring diabetes. We established that it could also be used to tell you if you are suffering from sugar, if you are feeling sick and have never had sugar, but the random sugar is very high. We said the best use of the random blood sugar is to test or “ping” the system to see if the medication being used for treatment of diabetes is working.{{more}}

This week, we will look at the fasting blood glucose or sugar (FBS). Most diabetics are acquainted with the FBS because it is used by the clinics to monitor the sugar. In fact, even though it can be used to give an idea of the sugar control, its main use is in the diagnosis of diabetes. Diagnosis means telling you that you have sugar when you do not know you have it. In other words, when you become ill and go to your doctor, he or she listens to you and examines you, they suspect that you have diabetes and do your random sugar. If the random sugar is very high, they diagnose you diabetes, but will still send you for a FBS, as it gives an idea of how “bad” the sugar is. We in public medicine continue to use the FBS regularly and routinely. As I said last week, because many of our diabetics are poorly controlled, the FBS is usually the lowest reading of the day, so many diabetics continue to use this test, as it gives them a false sense of control. When they are confronted with other tests that show that their sugar is not controlled, they become “defensive” and say “but my fasting sugar was good today”. So the fasting sugar can give you a false sense of security. Both the FBS and RBS are static tests, that is they tell you what’s happening at the moment and we are left to guess what the sugar control is like unless we test the sugar levels two or three times a day. This can be very tedious and painful, so we doctors use a test called the hemoglobin A1c or HbA1c.

The HbA1c (called A1c for short) is a test that was designed specifically to monitor diabetes. Hemoglobin is the protein in red blood cells that carries oxygen through our bodies so that we can live. A small amount of hemoglobin (about 5%) normally has sugar attached to it (called the glycosylated hemoglobin). Diabetics generally have a higher percentage of hemoglobin with sugar attached to it. The body destroys and remakes half of its hemoglobin every 10-12 weeks or every 3 months, so the HbA1c gives us a “bird’s eye view” of the sugar levels over the last 2-3 months. This means it gives us a very good view of how well the sugar has been controlled over the last 3 months. I have patients who do not take their medication until a week before coming back to see me. In the office, their sugars are controlled, but when you look at the A1c it is bad. You know therefore that for months before his visit the patient has been non-compliant, because his sugar was out of control for a long period of time before the visit. The A1c is not just about compliance (are you taking your medication or not), but also about control (is your sugar high or low). You may be compliant, but the medication is too strong or not strong enough and it will be reflected in the A1c. If your medication is too strong (less common) then the A1c is usually less than 5% and you may experience hypoglycemic episodes or you are always hungry. If your diabetes is poorly controlled (more often than you’ll want to believe) then the HbA1c will be high (usually more than 10%). A well-controlled diabetic will have an A1c of 7% or less, while a reasonably uncontrolled diabetic will have an A1c of between 7 and 10%. A poorly controlled diabetic will have an A1c higher than 10%. The A1c is not the real sugar level but you can have an idea of the average glucose by using the estimated average glucose. These can usually be gotten from a conversion chart. An A1c of 7% corresponds to an estimated average sugar level of 9mmol/l and an A1c of 10% corresponds to an average sugar of about 15.5mmol/l.

For comments or question contact:
Dr Rohan Deshong
Tel: (784) 456-2785
email: deshong@vincysurf.com