Does diabetes start with insulin resistance?

Insulin resistance refers to insensitivity of your body's cells to the hormone insulin, which normally signals cells to internalize glucose from the blood. Insulin resistance causes glucose to build up in the blood, which can lead to severe complications. If your cells are moderately resistant to insulin, you may have pre-diabetes; if insulin resistance severely impairs glucose metabolism, you may have diabetes.

Testing insulin resistance in your blood

The two principle tests used to determine insulin resistance are the fasting plasma glucose test (FPG)and the oral glucose tolerance test (GTT). These blood tests determine blood glucose levels under different conditions. The results reveal different, important information about how your body regulates blood glucose levels.

The National Diabetes Information Clearinghouse provides these descriptions of blood glucose tests.

  1. Fasting plasma glucose test (FPT). Before blood is drawn you must not eat any food for 8 hours. This test measures your blood glucose when it is not influenced by the food you eat.
  2. Oral glucose tolerance test (GTT). For this test you must also fast for 8 hours. The difference is that you drink a beverage containing glucose and then a blood sample is taken two hours later. The test determines the level of blood glucose in the context of the ingested glucose.

What do insulin resistance results mean?

The results of the above tests are useful in diagnosing diabetes. Diabetes is diagnosed when your glucose metabolism is severely impaired, which may be causing symptoms like fatigue and ongoing thirst. Pre-diabetes is diagnosed when glucose metabolism is somewhat impaired by insulin resistance, but symptoms have not yet appeared. The test results are expressed as mg (milligrams) of glucose in each dL (deciliter) of blood. The blood glucose levels that correspond to normal, pre-diabetes, and diabetes levels are:

FPG test:

  • Normal: At or below 99 mg/dL
  • Pre-diabetes: Between 100 and 125 mg/dL
  • Diabetes: At or above 126 mg/dL

GTT test:

  • Normal: At or below 139 mg/dL
  • Pre-diabetes: Between 140 and 199 mg/dL
  • Diabetes: At or above 200 mg/dL

If results indicate possible diabetes, it is important to repeat the tests on another day to confirm the diagnosis. Of course you'll want to discuss these results with your doctor for details about managing pre-diabetes or diabetes.

When to get tested for insulin resistance

Your doctor may suggest you have your blood glucose tested if you are over 45, as increased age is a significant risk factor for type 2 diabetes. If you are overweight, obese, or very obese, your doctor may suggest a glucose test even if you are younger than 45.

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