Recently I received an e-mail with the following question, and think it's worth some commentary: "I have type 2 diabetes and it's like a yo-yo. I'd like to know exactly what a good number is."

I've always had a simple answer to whether blood glucose (BG) numbers are "good" or "bad:" they are neither! They are simply numbers: high, in the target range, or low, but there's no goodness (nor badness) in a number.

More important, to answer the question, are several hidden issues:

* First, does the patient have proper technique to check their BG? Not only knowing how to calibrate and use the meter, but are they checking routinely before meals, or after meals (and if so, how long after eating), or both before and after? And how often?

* And how big is the yo-yo effect? If the patient is occasionally checking after a big meal and comparing the value to what they get before meals, the "spread" will be a lot bigger than if they are only checking before meals.

* Is the patient checking before breakfast, and finding that it's high compared to before other meals? That's probably due to the "dawn phenomenon," in which night-time release of other hormones can cause early-morning elevations of blood glucose levels.

* Is the patient perchance on a diabetes program that includes varying insulin doses? If so, it's possible that the instructions provided to the patient about insulin adjustment are actually causing a roller-coaster effect, and if so, the insulin instructions need to be changed.

* Is the patient on a stable meal plan, stable exercise program, and have stable stress levels? If any of these are changing from one moment to the next, it's no surprise that the BG levels would fluctuate.

Now, back to the question: where should the BG levels for someone with type 2 diabetes be? Well, ideally, you might think that all people with diabetes should be aiming for normal levels. But there's plenty of evidence that normalizing all BG levels is extremely difficult, and carries a risk of accidental hypoglycemia. That has to be balanced against the reverse observation: that elevated BG levels mean elevated risk of diabetes complications, including eye, kidney, and nervous system damage. So any pronouncement about where BG levels should be must be tempered with caution.

It's my feeling that all patients with diabetes should be treated to avoid numbers higher than 400, and to avoid numbers lower than 60: there's an increased risk of acute complications of nausea and vomiting, dehydration, and subsequent nasty things if BG levels are in the 400's -- and clearly the risk of hypoglycemia is dramatically elevated if BG levels are below 60. So there's a starting point for where to aim.

And the ultimate in BG control would probably be to keep almost all (maybe 90%) of before-meal BG levels between 70 and 100, and after-meal BG levels below 150. That's a goal that's pretty close to what non-diabetic patients might have. Is it possible? Sure, even if you have type 1 diabetes: if you are on an insulin pump or multiple insulin doses, testing 4-10 times a day, and motivated to continue doing so for a prolonged period of time. (The best example of motivators might be pregnancy: young women with type 1 diabetes who are planning pregnancy, or are pregnant, would be potential candidates for an ultra-tight diabetes control program aiming at numbers like these.)