By: Jan Chait
Knitters know that, for a perfect match, you need to buy all the yarn for a project from the same dye lot to eliminate subtle changes in color that can make your solid red sweater come out looking like it has stripes. The reason? Minute changes in dyes that cause just the slightest difference in hue.
It’s a similar scenario with the strips you put in your meter to test your blood glucose: Minute changes in batches of the chemicals that make up the reagents in the strips can cause fluctuations in readings.
Unlike slightly mismatched yarns, however, mismatched codes between strips and meters can cause erroneous blood-glucose test results. To avoid getting an error in your blood-glucose readings, you need to calibrate your meter so that its code matches the code—or number—stamped on the strip container.
“All blood-glucose meters use whole blood, which is applied directly to the reagent,” says Edie A. Elkinson of the Chico Chandler Agency in New York City, which represents the Ascensia line of meters from Bayer. “The reagent itself measures the amount of glucose dissolved in the plasma portion of the whole blood. The red cells are left on top of the reagent, and the liquid plasma with dissolved glucose diffuses into the reagent to be measured.”
The reagent in the strips is composed of a mixture of raw ingredients that vary from batch to batch. As Elkinson explains, “There is a certain amount of manufacturing variability due to raw materials, manufacturing lines and environmental conditions. It is very difficult or nearly impossible to reproduce the same reagent batches time and time again.”
It’s that variance that calls for coding your meter each time you open a new box or vial of strips. Some meters include chips to insert, others require you to reset numbers on the meter to conform with the code and some—including Roche’s Accu-Chek Compact meter, which has a bar code on the drum of strips—automatically calibrate the meter for you.
When you insert the chip that “tells” the meter what the code is, or when you manually change the numbers on the meter to change the code, “the calibration code assigned to a [specific] lot of test strips provides an internal adjustment to the [meter’s] glucose reading algorithm,” says Holly Kulp, vice president of professional relations and customer service at TheraSense in Alameda, California. “This means the strip and meter will perform together as a highly accurate system.”
How do companies determine the accuracy of each batch of reagent? They test it, using control solutions and, in some cases, whole blood.
Roche is one company that tests reagents using whole blood, in addition to using control solutions, says Nancy Lonsinger, director of consumer marketing for Roche Diagnostics in Indianapolis, Indiana.
No, Roche does not go to the blood bank to make a withdrawal. Instead, the company pays people to stick their fingers and contribute a drop of blood. Being paid to test? What a job!
Batch-by-batch testing, using both control solutions and whole blood, “is the best method to correct for small variations rather than a range of performance,” according to Lonsinger. “We uniquely set codes for each lot, [and] each set of strips is set for a unique code.”
As Elkinson notes, “Studies have shown that [many] users do not code their meters properly or are not aware that this should be done.”
This was borne out by a recent discussion on a diabetes mail list. Some members believed that the code numbers on the strip containers were not calibration codes but, rather, indicated the age of the strips: the lower the number, the older the strips. Not so. Expiration dates are clearly printed on the outside of the box in which the strips are sold as well as on the individual vials.
While all of the representatives contacted acknowledge that errors are generally small if the meter is not calibrated to the strip reagent lot, all agree that it is important to recode meters that need to have codes set.
“There is a potential that readings on the meter may be less accurate,” Lonsinger cautions, adding that while result errors may be minimal in most cases, “on rare occasions [errors in readings] may be significant.”