Diagnosing Diabetes

Diagnosing diabetes centers on testing the blood glucose and there are different types of tests available.

Perhaps the best test for diabetes is one known as the hemoglobin A1c or the glycated hemoglobin test. This is a simple serum blood test tells the percentage of the hemoglobin molecules circulating in our blood stream which have an attached sugar molecule to them. In effect, it measures the average of one’s blood sugar level over the past two or three months and therefore is considered very reliable. When the hemoglobin A1c result is 6.5% or higher, this means diabetes.

Of note, a hemoglobin A1c level between 5.7% and 6.4% indicates pre-diabetes. It is usually recommended to have two separate tests before instituting treatment, although in many cases, treatment consisting of a change in diet with reduced carbohydrate intake, increased exercise, and weight loss should be done immediately.

Fasting blood glucose is the most common traditional test for diabetes, and if the fasting serum blood sugar level is over 125 mg/dL on two separate occasions, this means diabetes is present. Of note, when the fasting blood sugar level is between 100-125 mg/dL, this is considered pre-diabetes.

Additional blood tests include the oral glucose tolerance test in which an initial fasting blood sugar is measured, and then a sugary oral beverage is provided followed by additional blood sugar measurements after two hours.

Testing for ongoing diabetes treatments and maintenance:

The most commonly used test for monitoring of blood sugar control is the hemoglobin A1c. Uncontrolled diabetes will be indicated by higher levels of hemoglobin A1c, reflecting the level of blood sugar over the last two to three months. Once proper diet, exercise and medications have been instituted, the hemoglobin A1c level should fall, indicating better diabetes control.

Day-to-day measurements of blood glucose levels are an important way to monitor the effects of treatment and avoid sugar levels that are too high or too low. Many commercially-available home glucometers are used by millions of people to monitor their blood sugar levels. For some people with diabetes, blood sugar measurements must be taken at home many times a day.

Who should be tested for diabetes?

People with symptoms:

Most people do not have many symptoms when diabetes is first setting in or the symptoms can be very subtle. If symptoms are occurring, they can consist of fatigue, increased thirst, increased urination, unexplained weight loss, blurry vision and frequent infections. More advanced symptoms stem from the tissue and organ damage that has occurred from diabetes over a longer period of time. These can include worsened visual impairment, numbness of the feet and toes, chest pain, heart attacks, high blood pressure and non-healing or very slow-to-heal sores and wounds particularly of the feet.

The earlier symptoms of diabetes occur because of the elevated blood sugar and the effects this has on the tissues. The elevated blood sugar reaching the kidneys leads to a higher volume of urine production and often leads to more frequent urination and getting up in the night to urinate. This, in turn, leads to dehydration and excessive thirst. Effects on the lens of the eye cause blurriness and stem from the high blood sugar and the changes in osmolality experienced by the lens.

Later, more serious complications of diabetes stem from nerve damage and arterial and blood vessel damage, impairing the sensation and the circulation to body tissues such as the kidneys, retinas, the peripheral tissues of the toes and feet, and the heart.

What is Insulin Resistance?

The term “insulin resistance” is offered as the primary explanation for our understanding of Type 2 diabetes.  But what is insulin resistance really and what does it mean inside our bodies?

One of insulin’s primary actions within the body is to facilitate delivery of glucose as a fuel source into the cells of the body, notably the muscle cells and fat cells.  When these cells become resistant to the effects of insulin the glucose does not enter the cells, but instead remains in the circulating blood stream, and the plasma blood glucose levels rise.  The elevated circulating blood glucose leads to damage to multiple organs including small arteries, nerves and numerous organs.

A different set of events take place in the liver because the liver cells play an important role in glycogen synthesis, and glycogenolysis.  Glycogen is a form of fuel storage that can be made quickly available.  Insulin resistance in the liver can impair glucose storage as glycogen and it fails to stop the liver cells from producing more glucose for the bloodstream.

We think of insulin as only affecting the uptake by the cells of glucose, but in fact it also plays an important role in the uptake of circulating lipids.  When the fat cells are insulin resistant there is difficulty of triglycerides entering the fat cells for storage and thus we find elevating circulating triglycerides.  These elevated circulating triglycerides cause damage to the body, particularly to the inside lining of arteries in the form of atherosclerosis.

How does insulin resistance develop?

Increased body weight is strongly associated with insulin resistance.  Additionally, high fat intake is associated with insulin resistance, especially in animal subjects, but probably in humans as well.  High dietary fiber intake is associated with less insulin resistance or what we would call insulin sensitivity.  Omega-3 fatty acids are thought to reduce the insulin resistance associated with excess fat intake.  Fructose and thus high fructose corn syrup are both implicated in development of insulin resistance.

Chronic excess carbohydrate intake in the diet is also considered a causative factor for the development of insulin resistance.  This line of thinking has led to the understanding that certain foods produce higher circulating blood sugar after consumption when compared to others.  Some more complex carbohydrates may not produce the same elevation in circulating blood sugar that a more simple carbohydrate meal does.  This concept of differentiating among different types of carbohydrates based on their effect on the circulating blood glucose is known as the glycemic index.  Foods that have a higher glycemic index may have a greater effect on producing insulin resistance.

Another important hormone that should be mentioned in the context of insulin resistance is leptin.  Leptin may in fact be more important than insulin because it is viewed as a more long term master regulator of metabolism, glucose, hunger and insulin.  Leptin is produced by the fat cells and under proper conditions would normally create reduced hunger and serve to decrease calorie intake and stabilize our metabolism. However concomitant with insulin resistance, obese individuals develop leptin resistance and no longer experience any disruption in their sense of hunger and satiety despite excess calorie intake and body fat expansion.  Leptin resistance and insulin resistance usually go hand-in-hand in the development of Type 2 diabetes

Testing for pure insulin resistance is normally not done in clinical practice because it is known that insulin resistance is present when pre-diabetes or diabetes is present, especially in an overweight person.  Normally testing for true insulin resistance requires complex laboratory investigation with infusion of regulatory hormones and serum samples of multiple glucose measurements.  One of these tests is called a modified insulin suppression test and another is referred to as a euglycemic clamp.  From a practical perspective these are not usually important or necessary.  What is important; however, is measuring the hemoglobin A1c and fasting blood glucose.  The treatment for insulin resistance is the same as the treatment for pre-diabetes: lose weight, increase physical activity and reduce dietary carbohydrate intake.