If you’ve had diabetes for any length of time at all, you’ve probably seen lists of the signs and symptoms of high blood glucose dozens of times. Doctors and diabetes educators hand them out. Hundreds of Web sites reprint them. Most diabetes books list them. You likely know some of the items on the list by heart: thirst, frequent urination, blurry vision, slow healing of cuts, and more.
But have you ever stopped to wonder why these symptoms occur? How does high blood glucose cause frequent urination, make your vision go blurry, or cause all of those other things to happen? Here are some answers to explain what’s going on in your body when you have high blood glucose.
Setting the stage
High blood glucose (called hyperglycemia by medical professionals) is the defining characteristic of all types of diabetes. It happens when the body can no longer maintain a normal blood glucose level, either because the pancreas is no longer making enough insulin, or because the body’s cells have become so resistant to insulin that the pancreas cannot keep up, and glucose is accumulating in the bloodstream rather than being moved into the cells.
Blood glucose is commonly considered too high if it is higher than 130 mg/dl before a meal or higher than 180 mg/dl two hours after the first bite of a meal. However, most of the signs and symptoms of high blood glucose don’t appear until the blood glucose level is higher than 250 mg/dl. Some of the symptoms have a rapid onset, while others require a long period of high blood glucose to set in.
It’s important to note that individuals differ in their sensitivity to the effects of high blood glucose: Some people feel symptoms more quickly or more strongly than others. But each sign or symptom has a biological underpinning, or a specific cause behind the effect.
Hyperglycemia can be acute or chronic. Acute hyperglycemia lasts only briefly and is often the result of a high-carbohydrate meal, a missed dose of medicine, stress, or illness. Chronic hyperglycemia, on the other hand, is a state of long-term elevated blood glucose. It is often the result of undiagnosed diabetes or of an inadequate diabetes treatment regimen. Chronic hyperglycemia is arguably the more dangerous of the two, as long-term elevated blood glucose has a toxic effect on the body’s tissues. In fact, some of the signs of high blood glucose are actually the aftermath of cellular damage caused by high blood glucose.
Signs and symptoms of high blood glucose are often what lead people with undiagnosed diabetes to visit their doctors and, consequently, get diagnosed. But signs and symptoms of high blood glucose can also occur after diabetes is diagnosed and treatment has been started. It is a signal that your diabetes has slipped out of control.
The three polys
The classic symptoms of high blood glucose are polyuria, polydipsia, and polyphagia. In plain English, that means excessive urination, excessive thirst, and excessive hunger. Any doctor who hears this trio of complaints will reach for a blood glucose meter. But often, the person experiencing these symptoms doesn’t notice them right away. This is partly because they often creep up on a person in a gradual fashion, and partly because the signs and symptoms of high blood glucose aren’t well known among people who don’t have diabetes — or don’t know they have diabetes.
Here’s what’s behind these classic three symptoms:
Excessive urination. Polyuria is the result of a runaway biological and chemical chain reaction that feeds on itself. It starts in the blood, where high glucose concentrations osmotically pull intracellular fluid into the bloodstream. This is the body’s attempt to equalize the concentration of glucose in the blood with the concentration in the cells. By diluting the blood with intracellular fluid, the body brings the glucose concentration of the blood closer to normal. Initially, this increases the fluid volume of the blood while dehydrating the cells.