After-Meal
Glucose Monitoring: Something to Chew On
Evan David Rosen, M.D., Ph.D.
Assistant Professor of Medicine,
Harvard Medical School
Regular
readers of this column in Diabetes In Control know that I'm
pretty much a one-trick pony when it comes to diabetes. "Control
is King" is my motto, and helping you to get there quickly
and safely is what this is all about. Several studies performed
in both type 1 and type 2 diabetes have shown that tight glucose
control is the best way to avoid serious complications of diabetes
like blindness and irreversible damage to kidneys and nerves.
Virtually all of the many recommendations that doctors give
to patients relate to the goal of reducing blood sugar levels
to as normal as possible; from diet and exercise to oral drugs
and insulin, it's all about the glucose. Because blood sugar
levels can vary dramatically over the course of a day, physicians
put a lot of stock into a test called the hemoglobin A1c, which
provides an average of the blood sugar over the preceding three
to four months.
One situation where diabetic
control is taken super-seriously is during pregnancy. Lower
hemoglobin A1c levels have been associated with much better
outcomes than are seen in uncontrolled diabetes, including reductions
in the rates of miscarriage and birth defects. This relationship
between glucose control and safer pregnancy has been known for
a long time, but in 1995 a study was published that showed the
way to making this easier for many women. Instead of focusing
on blood sugar levels before eating, like most diabetics, this
study asked women to test themselves one hour after meals, and
to change their insulin based on those post-meal numbers. Lo
and behold, the women who followed this course of action (as
opposed to traditional pre-meal testing) had better glucose
control and healthier babies. Perhaps not surprisingly, this
study changed the way pregnant diabetics are managed almost
overnight.
This result got a lot of people
thinking: if after-meal (called "post-prandial" in
medical parlance) monitoring works so well in pregnancy, perhaps
it might be the way to go in non-pregnant people as well. There
has been considerable debate about this in the ensuing six years,
but very little good data to help guide physicians and patients.
Some information may now be coming to light, but before looking
at it, let's take a step back and consider some basic physiology
and pharmacology in diabetes.
When people talk about blood
sugars, they usually refer to fasting blood glucose. Many studies
have shown that controlling fasting blood sugars leads to a
reduction in hemoglobin A1c, and it makes intuitive sense to
people that a diabetic ought to have a near-normal sugar at
times when sugar is normally lowest. Many drugs, including long-acting
insulin (eg. NPH) and metformin (GlucophageTM), do their best
work between meals. Post-prandial sugars, on the other hand,
rise after meals, and then return to lower levels a few hours
later. An abnormal rise in post-prandial glucose may be one
of the earliest signs of diabetes, and drugs like acarbose (PrecoseTM),
miglitol (GlysetTM), and rapid-acting insulin lispro (HumalogTM)
work best in this time frame.
The question we're interested
in, of course, is which numbers are more important in determining
the hemoglobin A1c level? Is it the fasting and pre-meal levels
or is it the post-prandial glucose level? A few older studies
failed to shed much light, but new data may be accumulating
that post-prandial may be the way to go. In the most recent
study, patients were taking a sulfonylurea that did not adequately
control their blood sugars. Researchers then added either bedtime
NPH insulin to decrease fasting blood glucose, GlucophageTM
to lower pre-meal glucose levels, or HumalogTM to reduce post-prandial
levels. The lowest hemoglobin A1c levels were seen in the group
receiving HumalogTM, despite the fact that they had much higher
fasting blood sugars than the other two groups.
This was a small study, and much
larger groups of patients will need to be examined to see if
these trends hold up. It also remains to be seen if controlling
post-prandial blood sugars will lead to reductions in the things
that matter most, i.e. diabetic complications. For the record,
the American Diabetes Association released a Consensus Statement
earlier this year declaring that evidence was insufficient to
recommend the exclusive adoption of post-prandial glucose measurements
for non-pregnant diabetics. Still, all physicians who treat
diabetes have seen patients with near-perfect fasting and pre-meal
blood sugars but lousy hemoglobin A1c values. For such patients,
it might be reasonable to try a course of post-prandial monitoring,
and perhaps a little rapid-acting insulin to go with that after-dinner
mint.
References
1. de Veciana M., Major C. A.,
Morgan M. A., Asrat T., Toohey J. S., Lien J. M., Evans A. T.
Postprandial versus Preprandial Blood Glucose Monitoring in
Women with Gestational Diabetes Mellitus Requiring Insulin Therapy.
New England Journal of Medicine 1995; 333:1237-1241, Nov 9,
1995.
2. Postprandial blood glucose.
American Diabetes Association. Diabetes Care. 2001 Apr;24(4):775-8.
3. Bastyr EJ 3rd, Stuart CA,
Brodows RG, Schwartz S, Graf CJ, Zagar A, Robertson KE. Therapy
focused on lowering postprandial glucose, not fasting glucose,
may be superior for lowering HbA1c. IOEZ Study Group. Diabetes
Care. 2000 Sep;23(9):1236-41.
4. The American Diabetes Association
Website
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