Blood Glucose Self-Monitoring

The Gear

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The year is 1978. A gallon of gas costs 63 cents, disco is king, 8-track tapes are the rage, and the Camp David Accords have created peace between Egypt and Israel. Double Eagle II becomes the first balloon to cross the Atlantic Ocean, teachers strike nationwide in the United States, Pope John Paul II is elected, and Argentina wins the World Cup. The global population reaches 4.4 billion, and in the United States, 5.2 million people have diabetes. For around $400 ($1,500 in today’s dollars), those 5.2 million Americans with diabetes can, for the first time ever, buy a home blood glucose meter.

Called the Ames Eyetone, it weighs nearly four pounds, stands 7 inches high, and is 4.5 inches wide and 2 inches thick. It has to be plugged into a wall outlet for power. It looks remarkably like Spock’s tricorder on Star Trek: The Original Series. The Eyetone gives results in a blazing one minute.

Beam me forward

A lot has changed over the past three-and-half decades, both in the world generally and in the world of diabetes. Today, 34.2 million Americans have diabetes, and blood glucose meters have become such an integral part of daily diabetes management that it’s hard to imagine effective therapy and control without them.

Today’s meters are small, fast, and portable, and they are getting more accurate with each generation. Most of them interface with computers, and some have the ability to send data wirelessly to other diabetes devices.

But are you taking advantage of all that modern meters have to offer? Or are you still using your meter like it’s 1978? Are you testing smart, or just testing? 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.

Today’s monitoring kit

A modern meter “kit” has three elements: a meter, test strips and a lancing device. The meter is the brains of a monitoring system. Meters can be as small as a toenail clipper, but most are larger, about the size of a smartphone. The vast majority are battery-powered, using button batteries or AAAs, but rechargeable models are beginning to make headway in the market. While a few meters do nothing more than report blood glucose readings, most offer a wide variety of logging, tagging and reporting features. Some even sport extras like reminder alarms, test strip port lights to aid in nighttime checks, and in-meter analytics of blood glucose statistics.

Test strips most commonly come in vials of 25 or 50, and each strip is designed to be used once, for a single blood glucose reading. There are no universal or generic strips; they are proprietary and can be used by only one brand of meter.

A lancing device is a spring-powered, pen-size contraption that advances and retracts a small, sharp piece of metal called a lancet. The lancet pierces the skin, making it bleed, so that a blood sample can be obtained for measuring the concentration of glucose in the blood. Before there were lancing devices, people with diabetes simply held a lancet in one hand and jabbed it into a finger on the other hand. Clearly, lancing devices are one of the better diabetes innovations of all time.

All of this gear is commonly carried together in a small zipped case.

Meters: coded and self-coding

There are two basic types of meters: coded and self-coding. A coded meter is a technological workaround designed to compensate for test strip inconsistencies. Back in the day, the enzymes that power test strips were harvested from wild microorganisms, and the purification technology wasn’t sufficiently developed to ensure consistent quality from batch to batch. A code associated with a batch of test strips told the meter how much to adjust the test results either upward or downward to help compensate for batch-to-batch inconsistencies.

On older coded meters, there were three different methods used to “prepare” the meter for a batch of strips. Some meters used up-and-down arrow keys on the meter’s face to manually enter the code number assigned to each batch; others came with a coding “chip,” a small plastic tab with a circuit board that slid into the back of the meter to relay the code information to the meter; and still others used a test-strip-like coding stick to program the meter at the beginning of each batch of strips.

However, no matter which coding method was used, users frequently neglected to check the code each time they started a new batch of test strips. And the reality is that it’s easy to forget something you rarely do: A person might have had strips from the same batch for over a year before a different lot number arrived at the local pharmacy. But the result of using a miscoded meter is that the blood glucose readings are off. Sometimes they’re only a little bit off, but sometimes they’re off by up to 80%, which, for people taking insulin, can be a recipe for severe hypoglycemia (low blood glucose).

Over the past decade or so, test strip technology has changed fundamentally. First, purification techniques got better, and then strip enzymes began to be “built” using recombinant DNA technology, much like modern insulin analogs. “Perfect” enzymes can now be produced in assembly-line fashion, with little or no variation from lot to lot. This development gave rise to self-coding (also known as auto-coding or no-code) meters that are billed as being able to communicate their code information from strip to meter. Actually, in most cases, there’s no magic communication, just good manufacturing tolerances.

More about meters

Many meters have temperature sensors and will not function if the environment is either too hot or too cold. If you live in a warmer climate, leaving your meter in your car can be a real problem. Conversely, in colder climates, houses can be too chilly in the morning for a fasting blood glucose check. If you turn your thermostat down at night so that your house is cold in the morning, my advice is to sleep with your meter under your pillow to keep it warm.

In most cases, meters have a life span of about three to five years, and those that use disposable batteries typically need a fresh set once a year.

Test strips

No discussion of blood glucose monitoring would be complete without considering the precision and accuracy of meters and test strips. Anyone who’s ever done two tests in a row from a single drop of blood can testify to the lack of precision (or reproducibility) in the results of most monitoring systems.

As of this writing, the standards for FDA approval of a meter and strip system are plus or minus 20% accuracy, 95% of the time (compared with a lab blood glucose test). This means that if your blood glucose level is 100 mg/dl, a meter and strip that report a reading between 80 and 120 mg/dl in 19 out of 20 readings would be approved. 

How test strips are stored can also affect their accuracy. Strips are designed to draw in liquids and are sensitive to moisture in the air. The containers that test strips come in are lined with a claylike substance that serves to keep the inner humidity level down. Because of this lining, be sure to reclose the vial as soon as you’ve removed a strip for monitoring, and don’t transfer your strips to other packaging such as plastic bags. In general, strip makers say that like insulin, a vial of strips, once opened, is only good for 30 days (although some manufacturers list a useful life of up to six months).

Most strip makers recommend that test strips be stored in a cool, dry, environment, out of direct sunlight. The maximum safe temperature for most strips (usually listed on the vial or in accompanying literature) is 86°F. Minimum safe temperatures are not always specified, but when they are, they are often in the range of 36°F to 45°F. Virtually all strip manufacturers advise against storing strips in the refrigerator.

Beyond inherent accuracy issues and potential storage problems, a number of different substances in the blood sample itself can affect the accuracy of blood glucose monitoring results. This list includes elevated levels of serum uric acid, vitamin C and acetaminophen (brand name Tylenol), as well as high or low levels of hematocrit, the volume of red blood cells in the sample. Test strip accuracy can also be compromised by high altitudes.

Despite all their weaknesses, blood glucose test strips have gotten better and better over the years, and it’s likely that they will continue to do so. We should also recall that prior to blood glucose testing with meters, the standard way to assess diabetes control was to measure glucose in the urine, a procedure with substantially less accuracy that delivered information that was several hours old.

Test strips are expensive: On average, they cost about a dollar per strip at the retail price if you have no insurance or are underinsured. This expense has led to many creative efforts to get more than one use out of a strip. However, a modern test strip is really a miniature circuit board, and part of the design element is that the liquid blood sample completes a circuit inside the strip. If a used strip is placed in a meter, the meter detects the complete circuit and won’t start a test. While a strip can be disassembled and cleaned on the inside so that it can fool a meter into thinking the strip is unused, the results from a second test can be wildly inaccurate, as test strips function largely by use of various enzymes that react with blood samples. There’s only so much of whatever enzyme the manufacturer has put in each strip, and it gets largely used up by the testing process. There’s simply not enough left for a second test.

There are discussions on the Internet about cutting test strips in half to save money. Can this really be done? No, not anymore. Back in diabetes prehistory, things were different: There was a brief period between the longtime standard of checking glucose in urine, and the rise of the modern meter, in which stand-alone, color-shifting blood glucose strips were used. These strips required the placement of blood on the strip followed by additional steps of rinsing, careful timing, and comparing the color of the sample with a reference chart. (In fact, the Ames Eyetone was really just a color densitometer designed to read the precise color of strips like these.) These color-shifting strips could be cut in half, but a modern test strip is a complicated, electronic, “lab in a tab” that can’t be divided.

Lancets and lancing devices

There are at least as many different types of lancing devices as there are meters. Most are vaguely pen-shaped, but there’s an extensive range of designs. A lancing device has either a variable depth gauge or an adjustable nose cap to control the depth of the lancing needle’s penetration; a cocking mechanism; and a trigger (at least one model combines these last two actions for one-press lancing).

All lancing devices use disposable lancets, which are basically very small, sharp pieces of metal. Currently there are at least six different types of lancets, although the two most common types will fit into the vast majority of lancing devices in the field. In addition to these common lancets, there four proprietary systems: one that requires a unique flat lancet; one that uses a mini-lancet; and two that use different drums containing several lancets.

When it comes to the two styles of near-universal lancets, different brands have different needle diameters, ranging from 21-gauge to 38-gauge. The higher the gauge, the thinner the lancet. A thinner lancet is less likely to cause undue pain in many people.

You should never let anyone else use your lancing device, nor should you ever use someone else’s.

More to come

This article is part one of a four-part series on blood glucose self-monitoring. The next installment will cover proper lancing and monitoring technique. In the meantime, click here for some blood glucose self-monitoring field tips.

Want to learn more about managing blood sugar? Read “What Is a Normal Blood Sugar Level?” “Managing Your Blood Glucose Ups and Downs”, and “Making Your Blood Glucose Monitor Work for You,” then see our blood sugar chart.

Originally Published March 28, 2014

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