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Blood Glucose Self-Monitoring: Technique

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Today’s blood glucose meters are small, fast, and portable, and they are getting more accurate — and sophisticated — with each generation. Most of them interface with computers, and some have the ability to send data wirelessly to other diabetes devices. Some meters allow you to reapply blood to the test strip, if needed; others let you easily share your glucose data with your family members and/or doctors. Still others enable you to track not just your glucose levels, but your medication, carbohydrates and exercise, too.

But are you taking advantage of all that modern meters have to offer? Are you checking smart, or just checking? Are you even doing it…right? This four-part series on blood glucose self-monitoring will help you assess how you’re doing and guide you toward using your numbers to improve your control, not just fill up your logbook.

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What is type 1 diabetes?

Type 1 diabetes is an autoimmune disorder in which the immune system attacks and destroys the insulin-producing beta cells in the pancreas. As a result, the pancreas produces little or no insulin. Type 1 diabetes is also characterized by the presence of certain autoantibodies against insulin or other components of the insulin-producing system such as glutamic acid decarboxylase (GAD), tyrosine phosphatase, and/or islet cells.

When the body does not have enough insulin to use the glucose that is in the bloodstream for fuel, it begins breaking down fat reserves for energy. However, the breakdown of fat creates acidic by-products called ketones, which accumulate in the blood. If enough ketones accumulate in the blood, they can cause a potentially life-threatening chemical imbalance known as ketoacidosis.

Type 1 diabetes often develops in children, although it can occur at any age. Symptoms include unusual thirst, a need to urinate frequently, unexplained weight loss, blurry vision, and a feeling of being tired constantly. Such symptoms tend to be acute.

Diabetes is diagnosed in one of three ways – a fasting plasma glucose test, an oral glucose tolerance test, or a random plasma glucose test – all of which involve drawing blood to measure the amount of glucose in it.

Type 1 diabetes requires insulin treatment for survival. Treatment may also include taking other drugs to prevent kidney damage or to treat diabetes-related conditions such as high blood pressure.

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To measure the concentration of glucose in your blood, you put a strip in the meter, stick your finger with a lancing device to get a sample of blood, touch the tip of the test strip to the drop of blood, and wait for the result. It sounds pretty straightforward. But, of course, the devil is in the details.

Setting up

Let’s start at the start. Once you have your meter, strips, lancing device and lancet assembled, what’s the first thing you should do? While there’s no right or wrong answer, the most efficient way to get started is to put a strip in the meter. Once the strip is in the meter and, if it’s a coded meter, the code has flashed, the meter will do a self-test and then signal that it’s ready for a blood sample. The amount of time a meter takes to do its self-test varies by brand and model. This self-test is the main reason it’s more efficient to turn on the meter by inserting a strip first, before you lance your finger for a blood sample. It’s better to have the meter waiting for your blood than to have blood drying on your finger while you get the meter ready.

Speaking of getting a blood sample…

Lancing issues

The next step in measuring your blood glucose is to get some blood for the meter, and thus we arrive at one of the debates surrounding self-monitoring of blood glucose: Do you first need to clean your finger with an alcohol pad? The answer is no.

At one time, cleaning the lancing site with alcohol was the standard recommendation for self-monitoring. This advice stemmed from unsubstantiated worries about infection from the environment. But times have changed, and the evidence simply does not support the need to clean the skin with alcohol prior to lancing it. In fact, using alcohol may be counterproductive, as it can dilute the blood sample and lead to an erroneous result.

The only situation in which cleaning a lancing site with alcohol might conceivably be helpful is in a hospital, where the potential for contact with infectious pathogens is higher than in the rest of the world. But even so, bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and other hospital-dwelling menaces are tough bugs that are unlikely to be killed by lowly alcohol pads, and there’s no evidence that such pathogens can be spread through a finger-prick. A quick wash of your hands with soap and water will ensure that any surface residue that might interfere with the test is removed. Most notorious in this department is the residue of fresh fruit, but some brands of hand lotion, especially the scented kind, can also be problematic. Don’t forget to dry your hands before you do a finger-stick — water on your finger can dilute the blood sample and give you an inaccurate reading.

So your meter has a strip in it and is ready to rock and roll. The lancing device is loaded, cocked and ready. Where should you poke? Anywhere between the fingernail and the first knuckle of any finger is fine. Some people like to use the side of the finger, some people like the pad, and some people prefer the top. It doesn’t make any difference. It really comes down to the size and shape of your hands and the type of lancing device you’re using. Choose a spot that’s easy to get a sample from, but don’t play favorites. Use different fingers, and vary the exact lancing spot each time so that you don’t develop calluses.

I also advise people to avoid their little finger, simply because it often seems to be more sensitive than the others. Also, many people have difficulty lancing their thumb, while others find it easy and even preferable. Again, there’s no right or wrong choice when it comes to selecting a finger, nor any right or wrong choice regarding the lancing location on the tip of that finger.

Where there can be a right or wrong technique, however, is in the pressure you bring to bear on the lancing device. Timid folks barely kiss the skin with the tip of the device, while others mash it down to the bone. It’s important to be consistent. Apply the same amount of pressure to the device each time you use it so that you can adjust the lancing depth, if needed, and get repeatable results. The goal is sufficient blood with minimal cursing.

If lancing your finger makes you release a string of expletives more appropriate for the locker room or the deck of a merchant sailing vessel, then you’ve got the depth set too deep, or the lancet is overused and dull. You should feel something, but unless you have severe neuropathy, which can make lancing painful, lancing should not hurt.

On the other hand, if you have to milk your finger for five minutes to get a decent-size blood drop out, then you aren’t lancing deeply enough. A very gentle squeeze around the lancing site should cause the blood to well up. If you “milk” the site too much, with many meters you’ll get an inaccurate result because the sample is watered down with interstitial fluid (fluid surrounding cells in the body).

What about doing a blood sugar check on a site other than your fingertip? Alternate-site testing (AST) involves using another part of your body to check your blood sugar. These sites include the palm of the hand, the forearm, the upper arm, the thigh and the calf. Using another site can be helpful for people who experience sore fingers or who have difficulty getting a large enough blood sample from a finger.

AST may be an option for you, but always talk it over with your doctor or diabetes educator first. That’s because using AST may give a delayed result, and it may not give an accurate result if your blood sugar levels are changing rapidly — for example, after eating a meal, after taking insulin or during or after exercising. It’s also not recommended to use AST if you have hypoglycemia unawareness.

How much blood do you need? Newer meters require laughably small drops, about the size of a pinhead. Older meters need a significantly larger drop of blood. Failing to feed either type of meter enough blood will result in a frustrating error message at best, and a false reading at worst.

Many test strips have a viewing port at the top of the strip to indicate visually if they’ve received enough blood for a proper test. But as a means to double-check, there should always be a small amount of extra blood left behind on your finger, showing you that the strip drank its fill.

Now, what should you do with that extra blood? Most nurses and doctors are horrified to learn that most people with diabetes, especially the ones who test a lot, just lick it off their finger. Social norms aside, there’s no harm in this. Other people carry a tissue or cotton pad in their meter case to dab off their finger after testing, and that’s fine, too.

To dispel another piece of legacy mythology, it is no longer necessary to do a dual wipe: wiping away the first drop of blood and testing the second drop. In the early days of blood glucose monitoring, the amount of blood needed was much larger and the speed of the tests was much slower. The first drop of blood from a lancing site contains a greater volume of platelets, which could make the lancing site seal up before enough blood was obtained for the test, and the dual wipe ensured a longer, larger flow of blood. Additionally, the first drop of blood can contain a greater volume of interstitial fluid and/or higher potassium levels, either of which could throw off the results of the first generation of test strips. With the enzymes used in today’s test strips, and with the lower blood volume requirements and greater speed of testing, a dual wipe is obsolete and unnecessary.

Putting blood on the strip

Now that you have the meter ready to go, and an adequate drop of blood waits on your fingertip, is there any protocol for how to actually do the test? Yes. The best strategy is to bring the meter in at a 45° angle and touch the end of the strip to the very edge of the blood drop. The strip will suck in the blood like paper towels cleaning up spilled wine in those old TV commercials.

Don’t try to apply blood to the strip; the strip is designed to draw the blood into itself. Let it do its job. Also, shoving the strip deep into the blood sample seems to overwhelm the strip in many cases, leading to an error message and requiring you to start over with a new strip.

Generally speaking, the higher your blood glucose level, the longer a meter takes to display its reading. If your meter is silent for a while after the strip has sucked in the blood, know what to expect. Most of the meters on the market today take only a few seconds to display results.

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