Measuring Glucose The Choices

A recent conversation in a diabetes support group prompted this post when a member suggested using alternative sites to fingers to check glucose levels using what’s commonly known as a finger stick blood glucose meter.

Prior to the 1980’s we didn’t have a way to measure our blood sugar levels in real time but that all changed when the humble finger stick meter revolutionised diabetes. Now a mere 30 years later we actually have more options in how to measure our glucose levels with more innovations in development.

The Journey of a Glucose Molecule

Glucose starts out as carbohydrate and then we eat it.

“Glucose moves into the bloodstream from the intestine, specialized cellular transporters shuttle glucose across the cells that line the intestinal tract, where once through the intestinal lining, glucose is free to dissolve in the blood, and travels around the body. The intestinal transporters act quickly, such that blood glucose rises rapidly after a carbohydrate-containing meal. The pumping action of the heart then distributes blood glucose absorbed at the intestines to every part of the body” using the circulatory system of veins, arteries and capillaries.

It takes approximately 10 to 15 minutes for the glucose molecules to travel from the intestinal wall into the circulatory system and be transported throughout the body: from our deep veins into our capillaries and the fluid between cells.

So, it means that the most up to date glucose number you can have is from the intravenous blood supply, the capillaries in the fingertips and then the interstitial fluid.

Glucose Testing in blood

Blood Glucose Meter:

The most common method to check glucose and the most accurate is the finger stick method using a blood glucose meter. This is also known as Self-monitoring of blood glucose (SMBG).  

And while SMBG is the most accurate method of test glucose levels, it’s still not 100% accurate, 100% of the time. Since 2013, blood glucose meters can be wrong by 15%, 95% of the time and wrong by 20% 99% of the time.


“In 2013, the International Organisation for Standardization (ISO) announced improved standards for blood glucose meters.

Blood glucose meters now need 95 percent of measured blood glucose values be within 15 percent of the actual blood glucose level and that 99 percent of meter values be within 20 percent of the actual blood glucose level.

As for results in the hypoglycemic range, under the current guidelines, if your actual blood glucose level is 60 mg/dl, your meter could read between 45 and 75 mg/dl and still meet the standards. The new guidance says the reading would need to be somewhere between 51 and 69 mg/dl to meet accuracy standards.” From Diabetes Forecast 2015  

How to I make sure the results are accurate?

You can verify that your glucose reader and test strips are working together properly using the control solution that usually comes with the meter. If not, you can buy the control solution at most drugstores, or directly from the manufacturer. We recommend that you check the accuracy of your meter’s readings at least once a year by comparing a fasting reading with a reading done at the same time in a laboratory. Consult a health professional about the acceptable variance between the two readings. Also, always follow your meter’s user instructions.

To avoid false readings, your test strips and glucose meter must be in good condition. Make sure that:

  • The expiry date printed on the test-strip container has not been reached or exceeded

  • The test-strip container was not left open after you took out a test strip

  • The test strips are in their original container

  • The test strips have been kept away from moisture, and stored at a temperature between 4 and 30 degrees Celsius

  • The test strips have not been contaminated by dust or other substances

  • There is no dust or dried blood on the opening of the test strip

  • The glucose meter has not been left in direct sunlight

  • The glucose meter has not been exposed to moisture, or to temperatures below 5 degrees Celsius or higher than 30 degrees Celsius

  • The glucose meter has not been dropped, or been in contact with a liquid

Alternative site testing using a Blood Glucose Meter

The blood glucose meter can be used to check glucose in places other than your fingers.

This is known as alternative site testing. However, “alternate site” monitoring tends to produce significantly less accurate results than fingerstick monitoring.  This is likely due to the “lag time” inherent in alternate site testing – similar to that seen with CGM.” (from

AST can be useful for people whose skin around fingertips has become severely calloused or hardened. However, “it should be noted, however, that this sort of testing should only be used when blood sugar is stable (eg, before a meal or when fasting) and fingertip blood should be used if blood sugar may be changing rapidly (eg, after a meal or exercise).

Lancing devices may need to be adjusted to a deeper setting when using alternative sites. Some come with a cap to be added for AST.” From Pharmaceutical Journal.

Glucose Testing in interstitial-fluid

Using a Continuous Glucose Monitor CGM or Flash Glucose Monitor (Freestyle Libre)

The sensor for all of these monitors sits under the skin and the glucose (SG) readings are taken from your interstitial fluid, and not from your blood, like fingersticks. Interstitial fluid is the fluid that surrounds the cells of your tissue below your skin, and usually glucose moves from your blood vessels and capillaries first and then into your interstitial fluid.

A few points to remember when using a Continuous Glucose Monitor CGM or Flash Glucose Monitor (Freestyle Libre)

  • SG and BG readings will rarely match and are expected to be different

  • A greater difference between SG and BG will be seen when your glucose is changing quickly, such as after eating or after taking a bolus of insulin

  • And most importantly, always confirm with your BG value before deciding to correct a high or treat a low glucose

A Variety of Blood Glucose Meters

All glucose meters are different and as well as telling what your blood sugar number is they can have all sorts of additional features such as: a built-in bolus calculator, a light where the strip is inserting, connected to a smart phone app to log all your diabetes information, some even check for ketones.

You may carry this gadget with you a lot so it’s important to find one that fits into your life. It’s also worth mentioning, especially if you have type 1 diabetes that having a spare is beneficial for when the batteries die or the meter stops working.

Some meters are rechargeable using USB cables and use various batteries.

** Most meter companies will replace your batteries free of charge when they die.

How do I get a meter?

All meters are available through a pharmacy or your diabetes clinic and are only available to those who have been assessed as needing one to manage diabetes.  

How much does it cost?

The meter companies usually don’t charge for their glucose meters so they are available for free.

The test strips for the meter are available through the HSE’s Long Term Illness (LTI) Scheme and are also free to all persons with diabetes.

The most common glucose meters are from the following companies:

What if my meter breaks down?

All companies have a customer care line and this number can be found on the meter itself, the box it originated from or the lancet and testing strip box.  They will replace meters if necessary free of charge or talk you through the problem over the phone.

“Diabetes Ireland encourages members to register their meter so that if any upgrades or issues arise, the company can alert you.  Batteries or replacement meters and results logging diaries can be posted out free of charge from the meter provider. It is recommended that meters be changed every two years.

Meters for testing blood glucose levels are regulated by the food and drug administration (FDA) using guidelines from the ISO.”