There is no such thing as borderline diabetes! The method used to diagnose diabetes is absolute, with well-defined criteria on blood testing. By definition, an individual either has diabetes or does not. Most people who have been told they have "borderline" diabetes actually have diabetes. Their doctor may have wanted to avoid scaring or worrying them by actually coming out and saying that diabetes was present. This is not in the best interest of the individual, as it underplays the importance of diabetes, and gives a false sense of security. You could then miss out on important education to improve your health early in the course of the disease.
Some doctors will say that borderline diabetes is present if a state of "Impaired Glucose Tolerance" is present. This diagnosis requires an Oral Glucose Tolerance test, and defines a high reading after a drink containing 75 grams of glucose, but not high enough to make a diagnosis of diabetes (a reading between 7.8 and 11.0). This diagnosis should not be ignored, as it represents a stage of "pre-diabetes", from which many people will progress to diabetes. Furthermore, it represents an increased risk of heart and other diseases. Dietary management as well as other lifestyle changes should be instituted. In fact, in the future, we may be treating this with medication. Exactly the same could be said of "Impaired Fasting Glucose" where the fasting glucose is between 6.0 and 7.0. In other words, the fasting glucose is higher than normal, but not in the range of someone with diabetes. This too should not be ignored, because it can increase the risk of heart and other diseases, as well as the risk of diabetes in the future.