Enzyme Chemistry: GOX vs. GDH-FAD vs. GDH-PQQ

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

The enzyme on a test strip decides how the strip copes with two things: oxygen in the blood sample and non-glucose sugars. Both matter. A 2009 review of meter accuracy puts interfering substances and altitude on its list of error sources [2].

Glucose Oxidase (GOX)

Glucose oxidase (GOx) reacts with glucose and isn't fooled by maltose; the FDA's 2009 notice listed it among the strip methods that non-glucose sugars don't affect [1]. Its weak spot is oxygen. In a 2001 study, raising the oxygen level of blood samples lowered the results on amperometric GOx strips, mostly once oxygen tension passed 100 torr [3]. The authors recommended oxygen-independent strips for critically ill patients whose blood oxygen runs high or is hard to predict [3].

GOx hasn't disappeared from shelves. LifeScan's OneTouch Ultra 2 system uses glucose oxidase [4], and as of October 2026 LifeScan still lists the Ultra 2 meter and OneTouch Ultra strips [5]. Its newer OneTouch Ultra Plus Flex system uses GDH-FAD instead [6].

GDH-PQQ

Glucose dehydrogenase (GDH) strips sidestep the oxygen problem: in that same 2001 study, oxygen changes didn't significantly affect them [3]. One version, GDH-PQQ, pairs the enzyme with a cofactor (a helper molecule) called pyrroloquinoline quinone. Its flaw is specificity. In August 2009 the FDA warned that GDH-PQQ "cannot distinguish between glucose and other sugars," so those sugars push results falsely high [1]. Maltose is the best-known culprit; the notice also names xylose and galactose [1].

The harm came from decisions made on those numbers. From 1997 to 2009, the FDA received 13 reports of deaths linked to GDH-PQQ strips with documented sugar interference, all in healthcare facilities [1]. Ten of the 13 patients were on Extraneal (icodextrin) peritoneal dialysis solution, and patients had been given insulin guided by the falsely high readings [1]. The FDA's first recommendation to healthcare facilities was to avoid GDH-PQQ strips [1].

GDH-FAD & Mut. Q-GDH

The GDH versions in big-brand strips as of October 2026 use different cofactors. GDH-FAD uses flavin adenine dinucleotide, and we found it in the FDA clearance summaries for Accu-Chek Guide [7], Contour Next [8], OneTouch Verio [4] and FreeStyle Lite [9] strips. True Metrix strips use it too [10]. In a safety communication last updated May 19, 2026, though, the FDA recommends that True Metrix users move to another testing method when possible, because of a problem with the meter's E-5 error code [11]. Abbott's FreeStyle Precision Neo strips use a third version, GDH-NAD (nicotinamide adenine dinucleotide) [12].

The FDA's 2009 notice named GDH-FAD and GDH-NAD as unaffected by non-glucose sugars [1]. The labeling adds one exception. FreeStyle Lite, Contour Next and Precision Neo strips all carry a warning against use during xylose absorption testing [9][8][12].

Mut. Q-GDH refers to a mutant form of GDH-PQQ, the enzyme in Roche's Accu-Chek Aviva Plus strips [13]. Triglycerides and vitamin C (ascorbic acid) caused significant interference in its FDA clearance testing [13]. So did galactose, one of the sugars named in the FDA's 2009 warning [13][1]. The decision summary doesn't report a maltose result, so FDA records alone don't show how the mutant enzyme handles maltose. If you use icodextrin dialysis solution or another product on the FDA's interference list, which meter to use is a decision for your care team.