Q: I have three meters. But the same blood used on all three meters can result in three different readings. Just how accurate can these be? Should I just use one meter, no matter what the reading?
A: It's best to use one blood glucose meter consistently and to avoid comparing results between meters. Meters may use different methods of reading the glucose in a blood sample or a different type of strip. For example, some meters may give the plasma glucose reading, which can be 15 percent higher than a meter that reads whole blood.
The performance of meters (and other similar diagnostic devices intended for home use) is monitored by the Food and Drug Administration before the devices may be sold to consumers. Meters are assessed according to standards set forth in the International Standards Organization document 15197. The FDA is recommending the revision of current standards of accuracy because new technology has allowed greater meter precision.
Currently, a home-use meter is considered accurate if 95 percent of the values it gives are within 20 percent of the value assessed by laboratory equipment when the reading is equal to or higher than 75 mg/dl. When values fall below 75 mg/dl, near the hypoglycemic (low blood glucose) range, the meter value must fall within 15 mg/dl (or points) of the lab value. That means a true plasma lab result of 100 mg/dl could show up as 20 percent higher (120 mg/dl) or 20 percent lower (80 mg/dl) on a meter. A value of 70 mg/dl could show up as 55-85 mg/dl on a meter.
Twenty percent may sound like a wide variance, but keep in mind it's unlikely that every result on a home meter would be that far off the lab equipment result. In fact, a review of the last 31 meters the FDA cleared shows that about half of them could meet a tighter standard -- falling within 15 percent when the readings are above 75 mg/dl and within 10 mg/dl when the reading is less than 75 mg/dl.
Virginia Zamudio Lange, R.N., M.S.N., CDE, is a registered nurse, certified diabetes educator, and a past president of the American Association of Diabetes Educators.