Diabetes Basics Part 2: The Definition of Diabetes

The first piece in this blog series describes how someone without diabetes maintains glucose levels within the tight normal range of 4 to 8 mmol/L. Persistently higher glucose levels mean the beta cells of the pancreas can’t make enough insulin to keep glucose from rising. A diagnosis of diabetes is made when the glucose level after an 8 hour fast is 7 mmol/L or higher, and when glucose levels at any time are 11.1 mmol/L or higher. Diabetes is also diagnosed when a test called the hemoglobin A1c level or the A1c level – which is an index of typical glucose levels in the last 3 months – is 6.5% or higher. Glucose levels or A1c levels that are higher than normal but lower than the diabetes cut offs indicate that the person has prediabetes meaning that their glucose levels are not high enough to be called diabetes but are still higher than perfectly normal. These criteria are summarized in this table.

But where did these criteria come from? The observation that people can develop a disease that is linked to high sugar levels goes back to antiquity, well before anybody could measure glucose or any sugar. Indeed, the word diabetes mellitus reflects ancient observations that there were some people who urinated frequently, and whose urine was sweet smelling. Indeed, the word diabetes literally means “the flowing of sweetness”. The 19th century saw the development of urine tests for glucose and the recognition that high levels were linked to medical problems like blindness and foot infections. Subsequent studies done over the next 100 years showed that abnormal blood vessels in the back of the eye began to appear once glucose levels rose above the numbers in the table. That was the basis for choosing glucose thresholds that are used today to distinguish people with diabetes from those without diabetes.

Strictly speaking, therefore, the diagnostic glucose levels for diabetes were chosen because higher levels promote abnormal changes in the back of the eye. However, it turns out that diabetes-range glucose levels put people at much higher risk of a wide range of long-term health problems including blindness, kidney failure, amputations, heart attacks, strokes, dementia, and other problems. In addition, high glucose levels can acutely cause dehydration, low energy level, reduced wellbeing, and a variety of infections.

The good news is that medicine has developed a wide range of diet, activity, and drug related therapies that can very effectively reduce glucose levels into the normal in people with diabetes. These will be discussed in the next piece.

About the author

Hertzel Gerstein

Hertzel is an endocrinologist and professor at McMaster University who is in high demand as a speaker, advocate, and educator on diabetes-related topics. His research focuses on using large, international randomized trials to identify and test new ways of preventing type 2 diabetes, reducing serious health outcomes like strokes and death, and achieving type 2 diabetes remissions.