Blood glucose testing tutorial and key points
Blood glucose testing is very helpful if you have diabetes.
But many patients and doctors fail to understand how to make sense out of blood glucose testing.
Here I present a brief tutorial on blood glucose testing and share some key points with you.
I have worked in diabetes care since blood glucose meters became available in the early 1980s.
First, not everyone with diabetes needs to do blood glucose testing.
Some people can test just occasionally, maybe one to four times a week.
So who does fine testing just occasionally?
Those with Type 2 Diabetes who:
· are not on a drug, like insulin or sulfonylurea, that could cause low blood sugars and
· are under good control based upon previous glucose measurements and A1c and
· are feeling okay
Frequent blood glucose testing for those with Type 2 Diabetes who are under good control and not on insulin or sulfonylurea is simply a painful waste of time and money. A recent analysis of studies confirmed that frequent blood glucose testing testing was not helpful for these persons.
But a study published in 2011 suggests that if you are not using insulin and are not under good control, blood glucose testing can be helpful in getting under better control but only if your doctor knows what to do with the numbers.
Now, if you take insulin for control of your diabetes you should definitely be doing blood glucose testing.
For any of the following reasons:
· to help achieve and maintain good glucose control to stay healthy and prevent the “complications” of diabetes
· to detect hypoglycemia; that’s a too low glucose of below 70 mg/dl.
· to find out if your sugar is far too high or low when you are feeling unwell
So now you know who should test and why?
But what should you be aiming for in terms of target glucose levels?
In general, in adults who are not pregnant, we aim for before meal sugars of 80-120 and perhaps a bit higher at bedtime, 90-140.
Some people need to do blood glucose testing about 2 hours after meals.
The goal 2 hours after meals is 90-180 mg/dl.
Ideally, we would like those after meal sugars between 90 and 140.
Keep in mind that these are general targets. Your doctor should discuss your individual glucose goals with you.
Another way to tell whether you are at glucose goal is to measure your Hemoglobin A1c or A1c for short. This test gives an idea of your average sugar over the past 2-3 months.
We do an A1c quickly in our office. It takes 3 minutes and needs a drop of blood from a finger stick. The A1c is not affected by eating.
To tell whether your glucose control is good we need to examine and review both your glucoses from your monitor and the A1c.
The A1c does not tell the whole picture. The A1c is like the forest and the glucoses are like the trees. And sometimes the A1c can be very misleading. More on that in a future post.
A few general points: Be sure to use blood glucose strips that are not expired. Check the date. Some meters still give a reading if the strips are expired. But you’ll get screwy numbers with expired strips.
And some meters still need to have the code change when you use a new batch of strips. And keep strips in the airtight container they come in.
Be sure you do not have sugar on the skin of your fingers. Fingers contaminated with sugar on the skin will give a falsely high reading.
I hope you know that you don't have to use your fingers all the time. Most meters allow for alternate site testing, for example on your forearm or palm of hand. Those areas hurt less.
A visit with a certified diabetes educator (CDE) is a must if you have diabetes. The CDE can help you with all these details and more about blood glucose testing.
So okay, you know the target blood sugars and you are aware of these general points, how about specifics?
First remember that those who use insulin and who are not on a pump, do best if they are using a rapid-acting insulin before meals and a dose of long acting insulin daily. See my previous post on how to use insulin.
There are far less reasons to do blood glucose testing if you are taking NPH insulin (Humulin N or Novolin N) or premixed insulin like a 70/30 or 75/25 insulin. For several reasons, NPH and premixed insulins are simply inferior to the newer insulin analogs.
Although your meter records your blood sugars, it is very helpful to keep a written log or record of your blood glucose readings. Bring in your log to your doctor visits.
On the log it helps to include factors that affect your sugar including:
· the insulin dose you took at that meal,
· if you ate more or less than usual or the grams of carb in that meal
· if you were physically active around that time
· if you forgot to take your insulin
· if you were sick or were on a medicine that might affect your sugars
· if you felt strange at the time
That’s a lot to consider. A really neat, new, small meter, the iBGStar, works with the iPhone and allows you to record all these factors. The iBGStar app is free.
Most meter companies will provide software to allow you to download your blood glucoses and print those readings out.
An app called Glooko allows you to manage a logbook for most meters on the iPhone but you need a cable to download your sugars from your meter to the iPhone.
You can and should review your logbook, probably every week or so. Once you understand what to look for, you can detect patterns and trends so you can get your sugar under better control. The new One Touch Verio IQ meter can be helpful in showing trends or patterns.
Too often patients never examine their readings. They just wait until they see the doctor in 2 or 3 months?
And far too often even the doctor does not know how to make appropriate changes in insulin. Many just never learned.
But how to do you make appropriate changes in insulin?
Look for patterns and trends. And understand how insulin works.
The rapid acting insulins are Apidra, Humalog and Novolog. They all work for about 4 hours and start working in about 15 minutes. They have peak action, that's when they work the most, around 110-120 minutes after the meal. If you took enough rapid acting insulin before the meal then your blood glucose should be good before the next meal, about 4 hours later. If you did not take enough, you’ll be high. If you took too much, you’ll be low over the next 4 hours after that injection.
For example, Joe is taking 25 units of Lantus at dinner and takes 5 units of Apidra or Humalog or Novolog before dinner. These are his sugars before dinner and bedtime:
Before Breakfast Before Dinner Bedtime
145 128 212
137 152 233
112 117 199
He is not testing at lunchtime but you can see that his glucoses are not too bad at dinner or before breakfast. But they go up after dinner. That means his dose of rapid acting insulin is not enough for what he is eating at dinner. He needs more. You could not tell this unless he tests toward bedtime or about 4 hours after his mealtime insulin.
The Lantus insulin takes 2-3 hours to work. Lantus works over 24 hours. Lantus has no significant impact on his sugar 4 hours later.
Joe’s blood glucose testing is an example of how you can use pattern recognition to improve glucose control.
Here’s another: Lucretia is taking rapid acting insulin before dinner and Lantus at bedtime. This is her blood glucose record:
Before Breakfast Before Lunch Before Dinner Bedtime
122 199 128 145
117 176 153 158
99 203 133 127
108 189 111 139
Most of these sugars are not too bad. But you may see that Lucretia has a blood glucose rise from breakfast to lunch. In fact, her lunchtime sugars are her highest. She assures you that she does not eat or drink any caloric beverages between those two meals.
So how should Lucretia improve her sugars? Well she might try eating a lower carb breakfast but she enjoys her 2 slices of toast each morning. Okay, so that means she needs rapid acting insulin -Apidra, Novolog or Humalog- before breakfast.
And now, one last example of pattern recognition in blood glucose testing: Dave is taking Humalog before each meal and Lantus after dinner.
Before Breakfast Before Lunch Before Dinner Bedtime
183 89 114 136
199 123 118 119
172 63 191 127
The pattern you can see here is that Dave tends to have his sugar go up overnight. If he eats after his bedtime reading, that could be the reason. But he tells you no, that's not the case. So that means his glucose rise overnight is from his liver making too much glucose.
See a previous post on this topic. He needs more Lantus to fix that.
Now how about that high reading, the 191, before dinner? That probably can be explained away by his low sugar before lunch that day. He got low because he mowed the lawn that morning and forgot to reduce his insulin dose for breakfast. The physical activity drove his sugar down. For several reasons, high sugars tend to occur after an episode of hypoglycemia. That happened to Dave; his low at lunch caused a high reading at dinner.
Two important last points about blood glucose testing:
Once you are under good control you will likely be able to test less frequently. This is often the case for those with Type 2 Diabetes whose sugars vary less than persons with Type 1 Diabetes. But many with Type 1 Diabetes do not have to test, day after day, 4 or more times a day. They may be able to stay under good control with less frequent testing.
Last point: Don't make up your glucose readings in your logbook or written record. You’d be surprised to learn how many people fabricate their readings!
We figure it out sooner or later and it wastes our time and energy. The meter does not lie and when we review your meter readings we’ll see that they don't match your logbook or record.
Be honest. We won't yell at you.
And now I hope you know more about blood glucose testing.
As endocrinologists, we strive to help improve glucose control and keep our patients well.
And we have better and better tools to help people, such as continuous glucose monitoring systems like the Dexcom Seven Plus.
We can all thank the hard work and good minds of many scientists and entrepreneurs.