Dr. Leahy: There are not specific tests that a doctor can easily order to really quantify any of those.  And, in fact, the surprising and really almost silly answer is probably the best test we have right now to assess the adequacy of beta cell function is a blood glucose.  Because the reality is if you get someone who’s really insulin resistant -- like a pretty big guy who comes into your office -- who doesn’t have diabetes, if you measure an insulin level it’s going to be really generous.  It’s going to be high because he’s compensating for insulin resistance. 

Alternatively, if you have a little grandmother who comes in who weights 95 pounds who also has normal blood sugars if you measure an insulin level or C-peptide in her it’s going to be really small.  It might even be below the normal range because, again, she’s so insulin sensitive she doesn’t need a lot of insulin.  So you can’t simply measure in absolute terms a measure of insulin secretion or C-peptide and think that’s going to tell us much. 

The reality is if a glucose value is above a target range than there’s something wrong with beta cells and that’s probably a fairly gross way to think about this.