By Alan L. Rubin

When prediabetes becomes diabetes, the body’s blood glucose level registers even higher. The following sections discuss the evidence for diabetes and the symptoms you may experience with diabetes.

Diagnosing diabetes through testing

The standard definition of diabetes mellitus is excessive glucose in a blood sample. For years, doctors set this level fairly high. The standard level for normal glucose was lowered in 1997 because too many people were experiencing complications of diabetes even though they did not have the disease by the then-current standard. In November 2003, the standard level was modified again. In 2009, the International Expert Committee on Diagnosis and Classification of Diabetes Mellitus recommended using the hemoglobin A1c as a diagnostic criterion for diabetes, and the American Diabetes Association subsequently accepted the recommendation.

After much discussion, many meetings, and the usual deliberations that surround a momentous decision, the American Diabetes Association published the new standard for diagnosis, which includes any one of the following four criteria:

  • Hemoglobin A1c equal to or greater than 6.5 percent.

  • Casual plasma glucose concentration greater than or equal to 200 mg/dl, along with symptoms of diabetes. Casual plasma glucose refers to the glucose level when the patient eats normally prior to the test.

  • Fasting plasma glucose (FPG) of greater than or equal to 126 mg/dl or 7 mmol/L. Fasting means that the patient has consumed no food for eight hours prior to the test.

  • Blood glucose of greater than or equal to 200 mg/dl (11.1 mmol/L) when tested two hours (2-h PG) after ingesting 75 grams of glucose by mouth. This test has long been known as the oral glucose tolerance test. Although this time-consuming, cumbersome test is rarely done, it remains the gold standard for the diagnosis of diabetes.

Following is another way to look at the criteria for diagnosis:

  • FPG less than 100 mg/dl (5.5 mmol/L) is a normal fasting glucose.

    FPG greater than or equal to 100 mg/dl but less than 126 mg/dl (7.0 mmol/L) is impaired fasting glucose (indicating prediabetes).

    FPG equal to or greater than 126 mg/dl (7.0 mmol/L) gives a provisional diagnosis of diabetes.

  • 2-h PG less than 140 mg/dl (7.8 mmol/L) is normal glucose tolerance.

    2-h PG greater than or equal to 140 mg/dl but less than 200 mg/dl (11.1 mmol/L) is impaired glucose tolerance.

    2-h PG equal to or greater than 200 mg/dl gives a provisional diagnosis of diabetes.

  • Hemoglobin A1c equal to or greater than 6.5 percent gives a provisional diagnosis of diabetes. As the hemoglobin A1c rises from normal, the occurrence of diabetes rises with it. If the hemoglobin A1c is equal to or greater than 5.6, the patient has a threefold chance of developing diabetes in the next six years.

Testing positive for diabetes one time isn’t enough to confirm a diagnosis. Any one of the tests must be positive on another occasion to make a diagnosis of diabetes.

Examining the symptoms of diabetes

The following list contains the most common early symptoms of diabetes and how they occur. One or more of the following symptoms may be present when diabetes is diagnosed:

  • Frequent urination and thirst: The glucose in the urine draws more water out of your blood, so more urine forms, making you feel the need to urinate more frequently. As the amount of water in your blood declines, you feel thirsty and drink much more frequently.

  • Blurry vision: As the glucose level shifts from normal to very high, the lens of the eye swells due to water intake. This swelling prevents the eye from focusing light at the correct place, and blurring occurs.

  • Extreme hunger: Inability to get energy in the form of glucose into the muscle cells that need it leads to a feeling of hunger despite all the glucose that is floating in the bloodstream. Such hunger is called “starvation in the midst of plenty.”

  • Fatigue: Without sufficient insulin, or with ineffective insulin, glucose can’t enter cells (such as muscle and fat cells) that depend on insulin to act as a key. (The most important exception here is the brain, which does not need insulin to extract glucose from the blood.) As a result, glucose can’t be used as a fuel to move muscles or to facilitate the many other chemical reactions that have to take place to produce energy. A person with diabetes often complains of fatigue and feels much stronger after treatment allows glucose to enter his or her cells again.

  • Weight loss: Weight loss occurs among some people with diabetes because they lack insulin, the builder hormone. When the body lacks insulin for any reason, the body begins to break down. You lose muscle tissue. Some of the muscle converts into glucose even though the glucose can’t get into cells. It passes out of your body in the urine. Fat tissue breaks down into small fat particles that can provide an alternate source of energy. As your body breaks down and you lose glucose in the urine, you often experience weight loss. However, most people with diabetes are heavy rather than skinny.

  • Persistent vaginal infection among women: As blood glucose rises, all the fluids in your body contain higher levels of glucose, including the sweat and body secretions such as semen in men and vaginal secretions in women. Many bugs, such as bacteria and yeast, thrive in the high-glucose environment. Women begin to complain of itching or burning, an abnormal discharge from the vagina, and sometimes an odor.

A study in the November 2007 issue of Diabetes Care, however, showed that in a group of over 15,000 people being treated for diabetes, 44 percent of people with type 2 diabetes reported not one of the symptoms above in the previous year when given a questionnaire. It is no wonder that a third of people with diabetes don’t know they have it.

Similar symptoms; different diseases

Frequent thirst and urination are the most commonly recognized symptoms of diabetes, but diabetes mellitus is not the only condition that causes these symptoms. Another condition in which fluids go in and out of the body like a siphon is called diabetes insipidus.

Diabetes insipidus is an entirely different disease that you should not mistake for diabetes mellitus. Diabetes insipidus results when a hormone in the brain called antidiuretic hormone is missing or when the kidneys can’t properly respond to antidiuretic hormone. This hormone normally helps the kidneys prevent the loss of a lot of the water in the body. Other than the name diabetes, this condition has nothing to do with diabetes mellitus.