--the best test, if you can talk a doctor into writing a scrip for it, is a LONG GTT (4-5 hour) with both fasting glucose and insulin levels drawn before the glucose drink, and then half-hour draws until at least the end of the third hour, with insulin and glucose levels analyzed from each draw.

As Mrs. D notes, the fasting insulin level may be more revealing than the fasting glucose level. I have insulin resistance, with a high fasting insulin level and "normal" fasting glucose levels, and I know that means my body is overproducing insulin levels to keep my sugar levels in check.

But, the patterns of insulin and glucose rise and fall over the hours can also be very revealing--and half-hour draws helps to keep one from missing some of the patterns, which can happen rapidly. In my case, there is normally an initial glucose level rise in the first half-hour to hour, but not to diabetic levels, followed quickly by a major insulin level increase, which a couple of hours later drives my blood sugar down to levels below my fasting level. This causes the insulin spigot to stop abruptly, and then things normalize over the fourth-fifth hour. This is characteristic of reactive hypoglycemia due to insulin overproduction in response to challenge, and another sign of "pre-diabetic" impairment. It's why I'm very careful with carbs, try to eat a "Zone" type diet, do weight-bearing exercise to build muscle (which helps insulin utilization), and take R-lipoic acid (a known insulin normalizer).