Diabetes Test Strips: Accuracy Issues!!

Diabetes test strips and blood glucose monitors can give you alarming results if not handled properly. Read the accuracy issues below to be sure you are not wasting money, time and emotions! (Or, is it just me who gets ticked with a high blood glucose reading?)

1. Lab/meter Comparison: Blood sugar monitors should all be checked against the lab at least yearly to see if they are reading accurately. Don't test your blood sugar monitor against another glucose meter. Blood glucose monitors and diabetes test strips should read within 15-20% of what the lab reads. To do this, test your blood sugar within 5 minutes of having your blood sugar checked at the lab (fasting is preferable, but if not possible then do at least 3 hours after eating). Take the difference between the two readings and divide it by the lab reading. Then multipy by 100. If the glucose meter is accurate, consider repeating the test. If still not accurate, call the 1-800# on the meter and ask for a replacement.

2. Control solution: Call us skeptics, but most diabetes educators do not trust the control solutions that come with the blood sugar monitors. Why? Well, the control solutions are not your blood. They offer up a broad "range" of blood sugars which are "OK" for your meter to test at. Also, once opened, the control solutions will maintain their values for only 3 months or less depending on temperature and evaporation. So, there you have it. Check your glucose meter out against the real thing - your blood. Have a lab/meter comparison done.

3. Is blood sugar monitor coded correctly? According to a study of 201 users of blood sugar meters, about 16% had improperly coded diabetes test strips. A study by Bayer showed that miscoded strips are inaccurate over 90% of the time. Sometimes by as much as 43%! So a test of 110 mg/dL or 6.1 mmol could show as 157 mg/dL or 8.7 mmol (or the other way around!) Check to see if the code on the vial of diabetes test strips matches the code number on the display screen when the glucose meter is turned on. Meters are "coded" to match a particular batch of diabetes test strips. This calibration can be done by entering a code number into the meter or by inserting a code chip. Some diabetes test strips have the coding build in (like the Compact and many of the Ascencia meters). But, many of the popular meters by Lifescan and Freestyle don't. You need to "code" or "calibrate" your meter each time you open a new vial of diabetes test strips.

4. Loose diabetes test strips. If you take individual diabetes test strips into your purse or wallet this can affect the accuracy (unless they are foil-wrapped from the manufacturer). Also, try not to move the few remaining strips of one vial into the new vial you are opening if the code numbers don't match. And if you have one vial of diabetes test strips at home and one vial at work but just use the one meter - make sure the vials have the same coding. WAIT!!! Ahhh. . . and one more thing that a reader pointed out to me. Even if the strips have the same code, they may have different expiry dates! After transfering a few strips a couple of times, you could end up with some pretty outdated strips floating around in a vial! (Thank you dear reader!)

5. Age of blood sugar monitor: Old blood sugar monitors may be inaccurate simply because of age. But old diabetic meters also tend to need cleaning or the dirt/dried blood could affect the accuracy of the reading. Be sure to follow cleaning instructions from the manual to ensure accurate results. If you have a diabetic meter older than 5 years please consider calling the meter company (often there is a 1-800 # on the back of the meter) and asking for a free updated model. They should want to keep you as a customer buying their strips.

6. Expired diabetes test strips? Check the expiry date when the pharmacy gives you the diabetes test strips. If you don't feel you'll be using them before the expiry date, ask for another batch with a later date. A few times I've had patients complain to me of the pharmacy selling them strips that outdated the next month.

7. Correct unit of measurement: Be sure to check that your machine is reading in the unit of measurement you are accustomed to. The U.S. uses mg/dl whereas Canada and most other countries use mmol/L. Sometimes the blood sugar monitor can read in either unit and it might accidentally be switched. Check beside the actual number that shows up on the screen to see the unit of measurement. If not correct, visit your manual for instructions to change it or call the 1-800# on the back of the meter. (FYI to convert from mmol/L to mg/dl you divide by 18. To covert from mg/dl to mmol/L you multiply by 18).

8. Hi and Low: Know what the "Hi" or "Low" means if you see it on your machine. Each meter can be different. "Hi" for some blood sugar monitors might mean over 540 mg/dl or 30 mmol/L!! At the "LOW" reading, this is far lower than what we recommend for target blood sugars. If "Low" you should treat with fasting acting sugar like glucose tabs.

9. Underfilled? Most newer meter have under-fill detection of some sort. However, the old Elite used to beep after a few seconds even if the chamber wasn't full. People were getting readings lower than anticipated. Also, the Compact meter tends to "err" and waste strips if you don't hold your finger there long enough. It's a good practice to hold your finger to the strip for 1-2 seconds after the beep to avoid wasting diabetes test strips because of under fill.

10. Date vial opened? For some diabetes test strips, once you open the vial you should use the content of the vial within 3 months no matter what the expiry date (because of repeated exposure to air). The Accusoft products have lid with a preservative in it so are supposedly good up until the actual expiry date on the bottle. However, other vials of strips (like Ultra, Freestyle) are good for a limited time once the lid is opened (regardless of the expiry date). Check the information in your diabetes test strip box to be sure.

11. Storage of strips: Heat, humidity, temperature and exposure to air can all affect strips. I recall a person whose test vial was left open to the air (not humid or hot air) but the readings were over 100% off from the lab! (Making them read REAL high). When this person switched to a new vial of diabetes test strips, the sugar readings plummeted to normal (and the meter checked accurate against the lab).

12. Storage of meter: Don't leave blood sugar monitors in the car on hot or freezing days. They are just tiny little devices and you know how tempermental electronics are.

13. Hands washed?: Although most people don't need to wash their hands before handling diabetes test strips, be sure you haven't touched something recently that could affect your test result. Here are ones that got me: banana (no- not the peel the white yummy stuff); glucose tablet (I know - you're saying "duh". But I forgot and my finger feltclean.) and a drip of apple juice from the apple. If you get a "wonky" number wash your hands and do another glucose test to double check.

14. Arm or finger poke site? Some alternate site meters suggest that if you suspect your are having a low blood sugar or hypoglycemia you should not poke your arm. Instead, you should use your finger. Please read your meter insert carefully. Post prandial blood sugars, or those done after meals, may not be as accurate on the arm either. If in doubt, use your finger.

Accuracy of diabetes test strips and blood sugar monitors doesn't just affect your management of diabetes, it affects your piece of mind. You don't need the frustration associated with unreliable diabetes test strips. THE BEST blood sugar monitor is one that suits your needs and that includes the type of diabetes test strip it uses.

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Ready to move on?

Glucose Meter Recalls
Choosing the Best Blood Sugar Monitors
Guidelines for blood sugars.
Solutions for lowering fasting glucose levels
Solutions to lower lunch sugars
Solutions to lower supper glucose levels
Solutions to decrease bedtime glucose readings
Home: the indispensable 4 step process for how to lower glucose levels
Back Up to Diabetes Test Strips Accuracy

Good Luck and Good Health!

REFERENCES:

Meter manuals;

The effect of coding on the accuracy of blood glucose results obtained with the One Touch Ultra, Freestyle and Ascencia Contour blood glucose monitoring systems. John M Baum. Senior Clinical Research Scientist, Bayer HealthCare 2004

Raine C. Self-monitored blood glucose: a common pitfall. Endocrine Practice 2003:9(2):137-139.