Enzyme Chemistries: GOx vs. GDH-PQQ vs. GDH-FAD

Enzyme Chemistries in [Diabetic Test Strips](/sell-diabetic-supplies/)

A test strip works because an enzyme on it reacts with the glucose in a drop of blood, and a 2009 review of glucose meters names glucose oxidase (GOx) and glucose dehydrogenase (GDH) as two of the three enzyme reactions meters use [1]. GDH comes in versions named for the helper molecule, or cofactor, bound to it: PQQ, FAD and NAD are the ones found in strips [2]. The short version: GOx is very selective for glucose but sensitive to blood oxygen. GDH-PQQ ignores oxygen but can read other sugars as glucose, and GDH-FAD and GDH-NAD were the chemistries FDA named in 2009 as free of that sugar problem [2] [3].

What the enzyme does on the strip

Each enzyme strips electrons from a glucose molecule. The meter then reads those electrons, either as a color change or as a small electric current [1]. Where the electrons go first is what separates the two families. Glucose oxidase can pass them to oxygen, which produces hydrogen peroxide; glucose dehydrogenases, by definition, can't use oxygen and hand electrons to other acceptors [2]. In what the 2011 review calls second-generation sensors, that acceptor is a mediator, a chemical that carries electrons from the enzyme toward the electrode (our electron mediator article goes further) [2].

Glucose oxidase: selective, but oxygen-sensitive

GOx has the longest track record. The first enzyme electrode for glucose, described by Clark and Lyons in 1962, used it, and a 2011 review of strip enzymes calls GOx "the gold standard of glucose sensing" [2]. The version from the mold Aspergillus niger, still the most common source, reacts with glucose and very little else [2].

Oxygen is the trade-off. GOx can use oxygen as well as a mediator, so the same review lists changes in blood oxygen as the main error source for GOx systems [2]. The 2009 review describes what that looks like: high oxygen in people receiving oxygen therapy can push GOx meter results falsely low, while hypoxia (low blood oxygen) can push them falsely high [1]. It adds that GOx meters can overestimate glucose at high altitude [1].

GOx hasn't gone away. As of October 2026, FDA's device identification database lists OneTouch Ultra Blue strips in commercial distribution under the glucose oxidase product code [4]. The FDA-cleared Prodigy Astro system also uses glucose oxidase from A. niger [5].

GDH-PQQ: fast, but it reads other sugars

GDH paired with pyrroloquinoline quinone (PQQ) became a major strip enzyme. The 2011 review explains its appeal: its activity is more than 25 times that of GOx, which allows fast readings, and as a dehydrogenase it isn't affected by changes in blood oxygen [2]. The catch is breadth. The soluble PQQ-GDH used in strips also reacts with other sugars, maltose among them [2].

Here's what surprised us about how serious that became. In August 2009, FDA warned that GDH-PQQ strips can't tell glucose apart from maltose, xylose or galactose, sugars found in some drug products or formed when the body breaks them down [3]. A falsely high result could hide real hypoglycemia (low blood glucose) or prompt too much insulin [3]. From 1997 to 2009, FDA received 13 reports of death tied to this interference, and ten of those patients were receiving Extraneal (icodextrin) peritoneal dialysis solution [3]. The notice listed GDH-PQQ strips from Roche, Abbott and Home Diagnostics, and it told healthcare facilities to avoid GDH-PQQ strips [3].

Two later FDA clearances show two different responses. FreeStyle Lite strips were on FDA's August 2009 GDH-PQQ list [3]. In May 2010, FDA cleared new FreeStyle Lite strips with GDH-FAD in place of the GDH-PQQ chemistry of the earlier version [6]. Roche took the engineering route: Accu-Chek Aviva Plus strips, cleared in September 2011, use a modified (mutant) GDH-PQQ [7]. Even so, their labeling warns that blood galactose above 15 mg/dL causes overestimated results [7].

GDH-FAD and GDH-NAD

FDA's 2009 notice named these two, along with glucose oxidase, as methods not affected by non-glucose sugars [3]. FAD (flavin adenine dinucleotide) is the same cofactor GOx carries, yet FAD-GDH can't use oxygen [2]. Accu-Chek Guide strips use an FAD-GDH produced in the mold Aspergillus oryzae [8]. Contour Next strips pair FAD-GDH with an electron mediator [9].

GDH-NAD (nicotinamide adenine dinucleotide) has one practical quirk. Its cofactor isn't bound to the enzyme, so the strip has to supply it alongside a mediator [2]. FreeStyle Precision Neo strips use GDH-NAD [10].

Free of the maltose problem doesn't mean free of interference. The 2011 review lists xylose as the known error source for fungal FAD-GDH [2]. FreeStyle Lite labeling says not to use the strips during xylose absorption testing [6]; Contour Next labeling says not to test during or soon after one [9]. Precision Neo labeling warns of xylose interference at low glucose levels [10]. Glucose oxidase isn't immune either: Prodigy Astro labeling warns against testing during or after a xylose absorption test [5].

Which strips use which enzyme, as of October 2026

The market never settled on one chemistry. Roche's US site lists Accu-Chek Guide and Aviva Plus test strips [11], so a single brand sells FAD-GDH strips (Guide) and mutant GDH-PQQ strips (Aviva Plus) at the same time [7] [8]. LifeScan spans two families too. FDA's database lists OneTouch Ultra Blue strips under the glucose oxidase code and OneTouch Ultra Plus strips under the glucose dehydrogenase code [4]. FDA's 2009 advice still applies: strips can be sold under several trade names and manufacturers can change methods, so the labeling is the place to confirm which chemistry a strip uses [3].

What the enzyme name doesn't tell you

The tidy story, that GOx has an oxygen problem and GDH doesn't, holds at the level of the enzyme [2]. A finished meter is more than its enzyme, though. In a 2007 study of 286 patients at moderately high altitude, a GDH-based meter read significantly higher than the laboratory, while a GOx-based meter's difference from the lab wasn't significant [12]. That was one pair of meters, and its GOx result doesn't match the 2009 review's note about GOx at altitude [1]. Each FDA decision summary we read reports its own altitude testing, supporting limits from 10,000 feet for FreeStyle Precision Neo to 20,674 feet for the Contour Next One system [10] [9].

So the useful comparison is strip labeling against strip labeling, not one enzyme name against another (our interference testing article covers how those lists are built). FDA's 2009 notice also points out that laboratory glucose tests don't use GDH-PQQ [3]. If you or someone you care for receives icodextrin dialysis, a maltose-containing infusion or a xylose absorption test, which meter and strips to use is a decision for the care team.