Glucometers are wonderful instruments that have revolutionized the way that we manage diabetes. These instruments continue to become smaller in size and incorporate various features in them, like the ability to sort out fasting and postprandial values, communicating with other devices (like pumps) and reporting in standardized formats. However, patients and healthcare providers continue to doubt the accuracy of these meters. Some patients even reject them outright!

It is important to understand that glucometers use fingerstick capillary blood to estimate sugars. This is different from the laboratory where the blood is collected from a vein. However, the machine is internally tuned to reflect venous plasma sugars. In fasting state when the blood sugars are recently constant, the values of sugars of samples simultaneously collected from the vein and fingerstick should give nearly similar values. But after a meal, sugars may change rapidly and finger stick values may differ physiologically from the venous sugars. Further, a certain degree of inaccuracy is expected in biological samples estimated by different methods. This is true for comparisons between different glucometers and between lab and glucometer values.

The ISO standards recommend that 95 % of values with a glucometer should be within 20% of glucose values above 75 mg/dl (which means that if the real value of plasma sugars is 100mg/dl, glucometer should show values between 80 mg/dl and 120mg/dl) and 15 mg of glucose values below 75 mg/dl ( which means if the real value of plasma sugar is 60 mg/dl, then the meter should show 45 mg/dl and 75 mg/dl). Diabetes organizations have called for more accurate instruments. Consumers using these machines should understand this approved standard.

There are other factors that can lead to inaccuracies with glucometers which we will discuss in the following article.