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July 21, 2005

Blood Tests and Insulin Injections

Question from Delacour, Alberta, Canada:

On two different occasions, I have switched my daughter to a new meter that requires less blood, but have always gone back to the old one. Each time I switched, I always did a comparison reading from the same finger prick between the old meter and the new one. I also checked the meters with the control solution. The majority of the time, the readings were within a similar range. However, I have noticed though that, sometimes, if there is a discrepancy, it is a large one. Last night, I did my daughter's 4 a.m. check and got a reading of 21.4 mmol/L [385 mg/dl]. She was showing no signs of having a very high blood sugar so I double-checked it with two other meters. These readings were both in the 15 mmol/L [270 to 285 mg/dl] range. This morning, I got the same thing. From the same drop of blood, I got a reading of 7.4 mmol/L [133 mg/dl] and another of 19.3 mmol/L [347 mg/dl] from two different meters. This was a huge difference and normally I would give her extra insulin to correct the high and yet would do nothing out of the ordinary for the lower reading. I have contacted the meter company, but because the meters are reading within the set range with the control solution and the codes are set right, they say there is nothing wrong with the meter. I am aware that meters are not 100% accurate, but it is frustrating when you can't trust the reading it gives. Is this common? Am I possibly doing something wrong? Is there any other possible reasons for this to happen?

Answer:

There are many potential explanations for the differences in readings that you experienced.

First, you should be sure that your daughter’s fingers are completely clean. It’s possible that the first reading is contaminated with a small amount of food, which would result in a higher first reading compared with subsequent readings.

Second, many older meters are calibrated to whole blood instead of plasma, as most new meters are. This results in an 11% deviation.

Third, some meters are simply not as consistent as others are. In a presentation made at the 2003 Diabetes Technology Meeting in San Francisco, Mary Kimberly, Ph.D., from the Centers for Disease Control and Prevention, gave a session entitled Glucose Monitor Variability Project. The US government funded study, conducted with assistance from five blood glucose manufacturers, looked at the variability of results obtained in commonly used meters. The data presented included five meters, one of which had substantially more variability than the other four meters. Dr. Kimberly was unable to provide information on which meter this was, because the CDC agreed to remain blinded to the meters used during the study.

Given the many advances in blood glucose meters in the past couple of years, my personal recommendation would be to move to one of the new meters that requires very little blood and which produces results quickly. We have reviews of many glucose meters online to help you make a decision.

JSH