Three ways blood sugar is measured
- Fasting blood glucose The fasting blood glucose (FBG) test measures the concentration of glucose in the blood after an 8-12 hour fast. It only tells us how blood sugar behaves in a fasting state. It tells us very little about how your blood sugar responds to the food you eat.The upward limit of normal blood sugar at 99 mg/dL. Anything above that – but below 126 mg/dL – is considered “pre-diabetic”, or “impaired glucose tolerance” (IGT). According to glucose monitoring studies of healthy people, a normal fasting blood sugar is 83 mg/dL or less. Many normal people have fasting blood sugar in the mid-to-high 70s.While most doctors will tell you that anything under 100 mg/dL is normal, it may not be. In one study, people with FBG levels above 95 had more than 3x the risk of developing future diabetes than people with FBG levels below 90.
- Oral glucose tolerance test (OGTT) The OGTT measures first and second stage insulin response to glucose. You fast and then you’re given 75 grams of glucose dissolved in water. Blood sugar is measured one and two hours after.If your blood sugar is >140 mg/dL two hours later, you have pre-diabetes.If it’s >199 mg/dL two hours later, you’ve got full-blown diabetes. If your result is 139 mg/dL – just one point below the pre-diabetic cut-off – you’ll be considered “normal”.
- Hemoglobin A1c Hemoglobin A1c, has become more popular amongst practitioners in the past decade because it’s significantly cheaper than the OGTT test. This test is a rough measure of average blood sugar over the previous three months. A truly normal A1c is between 4.6% and 5.3%.The problem with the A1c test is that any condition that changes hemoglobin levels will skew the results. Anaemia is one such condition, and sub-clinical anaemia is incredibly common. It is important to never use any single marker alone to determine whether someone has a blood sugar issue.
What does it all mean?It means that glucose levels depend highly on context and whether all markers are elevated, or just a few of them. If you’re interested in health and longevity – instead of just slowing the onset of serious disease by a few years – you might consider shooting for these targets. But remember to interpret the numbers together.
|Fasting blood glucose (mg/dL)||<86*|
|OGGT / post-meal (mg/dL after 2 hours)||<120|
|Hemoglobin A1c (%)||<5.3|