More Diabetes Answers

Why does the average blood glucose from my meter give me a different number than the eAG?

In a recent post I explained how it is possible to tell you what your average blood glucose level has been for the past 2-3 months by knowing your HbA1c.  Although this is meant to be helpful it can sometimes be confusing.  Let's say you test your blood glucose 3 or 4 times a day.  If you have a memory meter it will probably tell you what your average has been in the last 14 or 30 days.  Let's say that average is 183 mg/dL (or 10.1 mmol/L).  If you look at the table comparing HbA1C to the estimated average glucose (eAG) you would expect that when your HbA1c is tested it will be 8.0%.  but what if your HbA1c comes back at 9.8%, almost two whole percentage points higher than you meter average would have predicted.  What is going on?  The problem is probably not with your meter or with the accuracy of the lab test.  If your HbA1c is 9.8% this means that for the past 2-3 months your average blood glucose level really has been somewhere between 226-240 mg/dL (12.6-13.4 mmol/L).  The average that your meter gives you is simply the average of all the blood glucose tests that you did.  If you only test before meals or when you are feeling low, for example, and are not testing after meals or when you feel that your blood glucose is high then your "meter average" will be an underestimate of what your actual average is; it is not adding in the higher numbers to the average.  On the other hand if your "meter average" is higher than the eAG from your HbA1c test this suggests that there must be times during the day when your blood glucose is low when you are not testing.

So you can really make good use of this eAG number.  If it suggests that your blood glucose levels are higher than you thought from the tests you are doing every day then you should consider testing one or two hours after your main meals to see if it goes high at that time.  If the eAG is lower than you expected then it is likely that your blood glucose level is going low at times when you are unaware of it.  This can often happen during the night when you are asleep so it might be a good idea to test then to see if that is happening.

It is certainly a good idea to discuss your eAG with you doctor and health care team if the results don't make sense to you.

What is the Estimated Average Glucose (eAG)?

One of the most important numbers that you should track if you have diabetes is your HbA1c number (sometimes called glycosylated hemoglobin or hemoglobin A1c or simply A1c).  the HbA1c number tells you what percentage of the hemoglobin protein in your red blood cells has got glucose attached to it.  If the number is high this tells you that your average blood glucose level for the past two or three months has been high.  I explain this in more detail in Chapter 7 of The Diabetes Answer Book.  For people who don't have diabetes the HbA1c will be between four and six percent.  If your diabetes is really out of control more than 10 percent of your hemoglobin will have glucose stuck onto it.  For most people with diabetes the HbA1c is between 6-10% (and if you can safely keep it closer to 6% than to 10% that is great).

Because most people are more familiar with thinking of their blood glucose levels the American Diabetes Association is pushing for laboratories to not only give people their HbA1c result but to tell them what their average blood glucose level must have been for the past 2-3 months to get that HbA1c number.  The reason that this is possible is because of a very well-designed study that was published in the Journal Diabetes Care in August 2008.  Dr. Nathan and his colleagues worked with 507 subjects (268 had type 1 diabetes, 159 had type 2 diabetes, and 80 did not have diabetes at all) at 10 international research centers.  Over a six month period each subject checked their own blood glucose 7 or 8 times a day at least three days a week (before and90 minutes after each meal, before bedtime and once in the middle of the night).  In addition they wore a continuous glucose monitoring system (CGMS) on eight days during the six months.  So each subject had about 2,700 blood glucose tests done during the six month period as well as having their HbA1c checked several times during the same six months.  By taking an average of all these blood glucose tests and comparing them to the HbA1c taken during the same period the researchers found a very strong and straight relationship between the two.  They were able to construct a table which shows the average blood glucose level for each HbA1c.  Ihave shown this for a variety of HbA1c levels in the table below.  So the next time you get told what your HbA1c test result is you can look at this table and see what your average blood glucose level has been for the past 2-3 months.  The middle column is in "American" units of mg/dL and the right hand column give the estimated average glucose in International units of mmol/L.

HbA1c	eAG (mg/dL)	eAG (mmol/L)
6.0	126	7.0
6.5	140	7.8
7.0	154	8.6
7.5	169	9.4
8.0	183	10.1
8.5	197	10.9
9.0	212	11.8
9.5	226	12.6
10.0	240	13.4
10.5	255	14.1
11.0	269	14.9

 

Do Continuous Glucose Monitoring Systems (CGMS) really improve your diabetes control?

I certainly hope so, but just like with so many things in life the difference between the hype and the reality is a bit sobering.  Although there had already been a few promising small trials with CGMS the first big randomized controlled trial in patients with type 1 diabetes was published on September 8th 2008 in the New England Journal of Medicine (a very prestigious and respected medical journal).  Let me describe the study and then try to explain what the results mean.

At 10 different medical centers 322 patients with diabetes were randomly assigned to use one of three CGMS devices (The DexCom Seven, the Minimed Paradigm, or the Freestyle Navigator) or to continue with traditional finger stick blood glucose testing only. They were divided into three age groups (8-14yo, 15-24yo and 25 or older, the average age in this last group was 44yo).  The average HbA1c level in these patients before the study started was between 7.6-8.0%.  They were already doing an average of six finger stick blood glucose tests a day.  They were mostly well-educated (three quarters of the patients or the parents of the kids had college degrees).  They were all doing intensive insulin treatment (80% were using an insulin pump and the other 20% were taking multiple insulin shots a day of both long-acting and fast-acting insulins).  In other words this was a highly motivated group of people who would be expected to do really well.

They were seen seven times in person during a six month period of the study.  In addition they had seven scheduled phone visits with the research team in between their in-person visits.  During these visits they were given advice and suggestions for how to interpret their glucose results and encouragement to change their insulin treatment and food and exercise to help keep their blood glucose as close to normal as they could while trying to avoid going too low (hypoglycemia).

Given everything that I have said the results were quite disappointing.  At the end of six months the only group who showed a significant improvement in their average blood glucose control were the older adults who got a drop of HbA1c of about half a percentage point (0.5%).  The group aged 8-14yo and 15-24yo showed no improvement in HbA1c compared to the people who continued to use traditional finger stick tests only.  Even more surprising to me was that none of the groups using CGMS had significantly fewer low blood glucose episodes (hypoglycemia).

What can we make of this?  It tells us that if you are highly motivated and are using frequent traditional finger stick blood glucose testing then you can achieve really good blood glucose control and that adding a continuous glucose monitoring system may not improve things much further.  Now I am quite sure that some of the patients in the study would say that the CGMS made them feel more secure because they knew what their blood glucose was all the time.  There probably were some patients who felt they could push their HbA1c levels closer to normal more safely by having the CGMS but clearly this was not seen in everyone.  The study was only six months long, too.  Almost any novel treatment will help improve HbA1c in a group of people with diabetes during the first six months, especially if they are being seen up to 14 times by an enthusiastic and supportive research team.  I worry that in a "real world" setting where people would get less close supervision and support and where the novelty of the CGMS might wear off after six months that the results might be even more disappointing.

Here are a few other things to think about.  None of the people in this study had their CGMS device automatically connected to their insulin pump.  This study was not testing an "artificial pancreas" set-up where the continuous glucose readings are automatically transmitted to the insulin pump which then automatically adjusts the insulin dose (I say more about that idea in The Diabetes Answer Book).  Studies like that will be done in the next few years and should give interesting results.  People who want CGMS because they think it will make their life "easier" may be disappointed, just as people who want an insulin pump so that they won't have to think about their diabetes so much are often disappointed.  Both of these technologies can be an amazing help to some people and with more studies we will learn more and more how to use them most effectively.

Truthfully I was expecting the results from this study to be much more impressive.  Clearly continuous glucose monitoring systems are not a "magic bullet" to make life with diabetes totally easy.  They may be a step in that direction, however, if we can figure out how best to use them.

How low is too low for blood glucose?

As I discuss in The Diabetes Answer Book there are debates between doctors and research scientists about what the best average blood glucose level (usually measured by a blood test called glycosylated hemoglobin or HbA1c) should be for people with diabetes.  Should the target be less than 8.0%, less than 7.0%, or what?  Should there be different targets for people with type 1 diabetes rather than type 2 diabetes?  Should the targets be different for older people than for younger people?  Are there dangers of pushing the HbA1c level too low?  This last question seemed to get a resounding "YES" as an answer when a study called the ACCORD trial was recently stopped because the people with type 2 diabetes who were in the group pushing to get their HbA1c as low as possible had worse cardiovascular outcomes (more of them had heart attacks and angina) than the group that kept their HbA1c levels a little higher.  The researchers were not able to prove that those bad outcomes were because the group attempting to get their HbA1c lower had more bad low blood glucose events (hypoglycemic attacks) and they couldn't tie it to a particular type of drug that those people were being treated with but it is still possible that those things (low blood glucose and particular drugs) were the cause of the extra bad heart outcomes.  We won't know until more larger research trial are finished.

Where does that leave you now?  I still think the best target for HbA1c is for you to try to keep it as close to the normal non-diabetic range as you possibly can without ruining your life with too much stress, expense, and problems like low blood glucosse levels and weight gain.  If you are older, or if you know that you already have coronary heart disease then a target for HbA1c between 7-8% is probably safer and better than one below 7.0% but no-one knows that for sure.  Whatever the target HbA1c level that you choose and that you achieve it is really important to do everything you can to reduce your risk of heart disease, anyway.  Don't smoke.  Eat a healthy diet.  Get regular exercise.  Get your blood pressure checked regularly and try to keep it below 130/80.  Talk to your doctor about whether you should be taking a statin drug, an ACE-inhibitor drug, and aspirin.  I talk about these things in more detail in the section of "Staying Healthy Longer" of The Diabetes Answer Book.  I'd be interested to hear what you think.

Alternative Therapies

Here are the questions I answered in chapter 29:

Chapter 29: Alternative Therapies

What are the best herbal supplements for someone with diabetes to take?

How will I know if  new supplement for diabetes is helping me or not?

Do people with diabetes need to take vitamins?

Should I take extra vitamin E?

Does alpha lipoic acid help diabetic nerve damage?

Will prescription medicines and over-the-counter drugs work differently if I have diabetes?

Will chromium or vanadium help lower my blood glucose?

Can I be sure that supplements contain what it says on the bottle?

If an herbal preparation contains lots of things, how do I know which ones are most effective?

Can herbal preparations revive the pancreas and make it start working again?

Does glucosamine make your blood glucose go up?

Does cinnamon make your blood glucose go down?

Are alternative therapies ever harmful?

Why are people with diabetes told to get flu shots and pneumonia shots?

Traveling And Diabetes

Here are the questions I answered in chapter 28:

Chapter 28: Traveling And Diabetes

Is it okay to travel if I have diabetes?

Will customs officials in other countries think I am a drug addict if I am carrying needles and syringes?

Will they have my kind of insulin or pills or glucose testing supplies in a foreign country?

Should I take extra supplies with me when I am traveling?

How do I deal with my insulin shots if I am traveling across different time zones?

Advanced Insulin Management

Here are the questions I answered in chapter 27:

Chapter 27: Advanced Insulin Management

Isn't is easier to use an insulin pump?

What are the advantages of an insulin pump?

What are the disadvantages of an insulin pump?

How good is inhaled insulin?

How does pramlintide (Symlin) work?

What are the benefits of using pramlintide (Symlin)?

What are the problems with pramlintide (Symlin)?

Insulin Management

Here are the questions I answered in chapter 26:

Chapter 26: Insulin Management

Why can I give the same dose of the same insulin two days in a row and get completely different blood glucose results?

What things affect insulin absorption?

Is it best to give the long-acting insulin in the morning or at night?

Isn't there insulin that lasts for twenty-four hours nowadays?

How would I know if my long-acting insulin is lasting for twenty-four hours?

What is the Somogyi phenomenon?

When is it okay to use only one type of insulin?

What are the advantages of mixing different types of insulin together?

What are the disadvantages of mixing different types of insulin together?

Is it better to use a syringe or an insulin pen?

How long does a bottle of insulin last once it is opened?

Does insulin really need to be refrigerated?

If I find a spot where it doesn't hurt so much why can't I inject there all the time?

What should I do if I take too much insulin by accident?

What should I do if I forget to take an insulin shot?

What is "brittle diabetes?"

Is there damage from long term insulin use?

Insulin Basics

Here are the questions I answered in chapter 25:

Chapter 25: Insulin Basics

Do people with type 1 diabetes always need insulin?

How do they make insulin?

Why are some types of insulin cloudy?

How many types of insulin are there?

Why should I take more than one type of insulin?

How high a dose of insulin can you give?

How can I decide what the best types of insulin are for me?

What are the differences between the fast-acting insulins?

How soon before a meal should I inject my fast-acting insulin?

How do you decide how much fast-acting insulin to give before a meal?

Isn't it better to give the insulin after the meal when you know how high the blood glucose has gone?

Is it ever okay to inject insulin after the meal?

What are the differences between the longer-acting insulins?

How do you choose the right size of syringe and needle?

Should my spouse or close friend know how to give me my shot?

How often should I change the needle on my syringe or pen?

Should I swab my skin with alcohol before injecting myself?

Where is the best place on my body to inject insulin?

What is the best system for rotating my insulin shots?

Going On Insulin

Here are the questions I answered in chapter 24:

Chapter 24: Going On Insulin

My doctor says I need insulin, now.  Is it my fault?

My doctor says I need insulin.  Does that mean my diabetes is getting worse?

I knew someone who went on insulin and died a month later, so does that mean insulin must be bad for you?

When is insulin a good idea for someone with type 2 diabetes?

Once you go on insulin can you ever come off it again?

Why can't insulin be given as a pill?

Won't insulin make me gain weight?