Evolution of Calibration (Coding)

Evolution of Calibration in [Diabetic Test Strips](/sell-diabetic-supplies/)

A strip code is a small set of numbers that tells a blood glucose meter how one batch of test strips responds to glucose [1] [2]. For decades, people had to hand that code to the meter themselves, first by typing in a number and later by inserting a chip or key. Mistakes were common enough that, by 2008, several manufacturers had engineered the step away [1]. As of October 2026, the FDA records for the main systems from Roche, LifeScan, Ascensia and Abbott say the user doesn't code them at all [3] [4] [5] [6].

What a strip code actually is

The enzymes on a strip are purified from microorganisms, and their activity varies from lot to lot. That changes how much electrical current a strip produces for the same amount of glucose, so each batch gets a code that calibrates the meter for it [1]. Roche describes the code as a set of parameters linking the strip's signal to blood glucose, worked out by its quality department across the whole measuring range for every batch [2]. Abbott puts it more plainly: each strip lot has its own calibration values, such as a slope and an intercept [7]. One thing a code never fixed was variation between strips inside the same batch [1].

A manufacturer has two ways to handle batch differences. It can keep them too small to matter clinically, which means tight production tolerances and throwing out batches that miss them. Or it can measure each batch and encode the result [2]. The history of coding is largely the industry shifting from the second approach toward the first [1].

Color charts and two-point calibration (1960s and 1970s)

Before meters, the "code" lived on paper. Roche's 2008 account of coding starts with printed color scales that could be adjusted to each batch [2]. Miles Laboratories' Dextrostix strip, patented in 1963, was read by matching its color change against a chart [8]. To turn that color into a number, Miles had the Japanese company ARKRAY develop a reflectance meter; a 2011 history in the Journal of Diabetes Science and Technology dates the resulting Eyetone's launch in Europe and the US to 1973 [8]. The Eyetone needed a two-point calibration before every test, which made it too difficult for most people to use at home [1].

The code number, then code keys (1980s to 2000s)

A 2008 review in the same journal places the start of modern home glucose monitoring at the moment meters replaced that calibration routine with one code number entered for each batch of strips [1]. Roche lists the next steps as barcodes read by the meter and then electronic code chips [2].

When the FDA cleared the Accu-Chek Aviva in April 2005, its code key came packed in the strip vial and plugged into the meter. The key also stored the strips' expiration date, and the meter told the user when the key had expired [9] [10]. LifeScan's meters still asked the user to set the code. In the FDA's 2011 comparison for the OneTouch Verio, the OneTouch Ultra 2 meter, cleared in January 2006, still had the user set a calibration code [11] [10].

Why miscoding mattered

Hand coding went wrong often. A hospital diabetes education program in Indiana checked meters at first appointments from January through May 2007, and 16 of the 65 patients whose meters needed a code number or chip, 25%, had them miscoded [12]. Four other studies with about 500 patients between them found lower but real rates: about 3% in two and about 16% in the other two [1].

The size of the error mattered too. In a 2007 study of 116 people, purposely miscoded meters showed maximal median biases of +29% and -37%, against +0.64% and -10.45% for correctly coded meters [13]. Simulations in the same study found that insulin doses calculated from miscoded readings were more likely to be wrong, and that meters which coded themselves did better than even correctly hand-coded ones [13]. Much of this research came from industry, so we read it with that in mind: Bayer HealthCare funded the 2007 study, and Roche and Abbott employees wrote the company papers we cite here [13] [2] [7]. Our article on calibration codes vs. no-code technology compares the two approaches side by side.

Auto-coding and true no-code strips (2000s)

That 2008 review describes three steps away from the typed code [1]. The earliest "no code" systems held strips in a cartridge, and the meter read the code from the package. Next came meters preset to a manufacturer's most common code, with off-code strip lots labeled for the company's coded meters instead. Finally, some manufacturers cut enzyme variation enough that every lot worked with one setting [1].

Roche took the cartridge route. Its Accu-Chek Compact Plus printed the batch barcode on the drum that held the strips, so changing the drum changed the code [2]. That meter is no longer sold in the US: every Compact Plus entry in the FDA's device identification database is marked as no longer in commercial distribution, the latest since November 2022 [14]. LifeScan's OneTouch Vita, cleared in October 2008, removed the manual code entry its predecessor required [15] [10].

Abbott's FreeStyle Lite took the manufacturing route, and here's what surprised us about how. FreeStyle strips use coulometry, which measures the total electrical charge from the glucose reaction. That charge depends on the volume of the sample chamber, so Abbott controlled lot-to-lot variation by controlling the chamber's dimensions, and shipped the meter with a single set of calibration values [7]. Older FreeStyle strip lots had never been screened against that setting. Abbott's fix was physical: it changed the strip's turn-on electrode so the Lite meter would not start with an older FreeStyle strip [7].

Not everyone saw coding as the problem. Roche argued in 2008 that the code chip's extras were worth the step: it could warn about expired strips and deliver meter firmware updates, such as a shorter test time [2]. Roche also reported that in worst-case modeling for its Aviva system, the chance of a miscoding error large enough to change clinical action was low [2].

Where coding stands as of October 2026

FDA records for the main current systems from Roche, LifeScan, Ascensia and Abbott all describe a meter the user never codes:

• Accu-Chek Guide (cleared August 2016): "does not require calibration or coding by the user" [3] [10].
• OneTouch Verio Flex (cleared July 2015): "automatically coded," with no calibration by the user [4] [10].
• Contour Next One with Contour Next strips (cleared November 2016): "a non-coding device" [5] [10].
• FreeStyle Lite: calibration "None required" in a May 2010 FDA decision summary [6] [10].

Two older systems that the companies still show on their US sites were coded meters in their FDA records. The Accu-Chek Aviva Plus, cleared in September 2011, used a code key that stayed in the meter until a new box of strips was opened [16] [10], and Roche's US site now says the Aviva meter "will soon be discontinued" [17]. The OneTouch Ultra 2, still on LifeScan's US site [18], had a user-set code in the FDA's 2011 comparison [11]. We couldn't find a current statement from either company on whether those meters still need a code, so the user guide that came with the meter is the place to check.

Removing the code didn't remove batch-to-batch variation. It moved the job from the user to the factory, where manufacturers keep differences small or reject batches that miss their limits [2]. How that consistency gets checked once strips are on pharmacy shelves is the subject of our article on post-market surveillance and lot-to-lot variability.