Blood Sugar Tests:Making sense of medicine

Have you ever wondered why blood glucose levels are not used to diagnose diabetes? After all, we know that diabetes is a disease of high blood sugar levels.

Blood glucose levels vary a great deal throughout the day. Shortly after you eat a meal, levels will rise as the sugars from the carbohydrates in the meal you just ate are released. This glucose is then picked up by the bloodstream to transport it around your body to fuel all your tissues. Blood glucose levels usually peak 30-60 mins after you eat a meal, and they will rise higher and faster if that meal was high in carbohydrates, especially if they were simple sugars. Ideally blood glucose levels should be back down to a fasting low level 2-3 hours after finishing that meal. 

Glucose levels will be at their lowest when you wake in the morning when you haven’t eaten or drunk anything since the night before. This is why a common blood sugar test is the fasting blood glucose test, which checks whether your blood sugar levels have gone down to a healthy low level overnight.

A random blood glucose test is sometimes done, but because of the wide variability in levels, it will only tell you if there is a big problem that takes your sugars way up out of the normal range. Usually it isn’t very helpful. 

Blood glucose levels only give you a snapshot of where the levels were at the moment the test was done. They can’t give you an overall picture of how your body is managing the sugars and carbohydrates you consume on daily basis, and not managing your blood sugar well is the first step towards diabetes.

So what is the best screening test for diabetes?

You may have seen HgbA1c in your blood test results and not realized how important it is.  It refers to Hemoglobin A1c, and this is how it works:

When blood sugar levels are high, some sugar sticks to our proteins, in a process called glycosylation. Hemoglobin is the protein in red blood cells that carries oxygen, so some of this sugar gets stuck to it. Because red blood cells only live for 3-4 months, we know that all the sugar on the protein seen on the hemoglobin tested is due to high blood glucose levels over the last 3 - 4 month period. The fact that blood tests are easy to do makes it relatively simple to check those red blood cells to see how much sugar has stuck to their hemoglobin. 

This doesn’t mean that only hemoglobin is affected: all proteins can become glycosylated. This is the mechanism by which diabetes harms various body tissues, including the eyes, the kidneys and the blood vessels.

This is also the reason why people with blood sugar problems can’t cheat by eating lots of sugar until the day before the test, then being very good for a day to fool their doctors. The HgbA1C test will give them away! This is also the reason it is the test for diabetes, because it tells us whether blood glucose levels have either been good or too high over a long period.

Given the prevalence of diabetes, and that testing is relatively cheap and easy, this is a test that is often done as part of a yearly physical.

And what is “Pre-diabetes”?

This is where HgbA1c levels are seen creeping upwards over time. This indicates that the body isn’t handling blood sugars as well as it used to, or that the diet is very poor, or maybe a bit of both. We SHINE doctors often say that we are at least as interested in how blood test levels are trending as we are in the absolute measurements. This is very true with HgbA1c: if your numbers are trending up, now is the time when an ounce of prevention is worth a pound of cure.

Fortunately there are lots of ways to help yourself if you are seeing this upward trend. Focus first on a better diet and increased exercise. Exercise uses up that glucose, both during the exercise, and for a while after (bonus!). Therapeutic fasting has been shown to help pre-diabetes as well as overt diabetes, as has going keto for a few weeks, then sticking to a healthy clean diet.

Want to learn more about blood sugars? Check out the SHINE Health Posts Blood Sugar Blues and Oh Sugar!