Multi-Analyte Strip Chemistry

Multi-Analyte Strip Chemistry

Every substance a multi-analyte system measures needs its own chemistry: its own enzyme, its own way of turning that enzyme's work into a signal, and its own space where the other reactions can't interfere. When we read the FDA files for blood glucose and ketone systems, the two enzymes turned out to be close cousins that hand their electrons to the same helper molecule [1]. Lipid panels take a different route. They split one drop of blood across separate reagent pads, and each pad develops its own color [2]. Our companion article, Multi-Analyte [Test Strips](/diabetic-test-strips/multi-analyte-test-strips/), covers which products exist. This one is about what happens inside them.

Glucose and ketones: two dehydrogenases, one cofactor

A dehydrogenase is an enzyme that pulls electrons off its target molecule. Many dehydrogenases need a cofactor, a small helper molecule that carries those electrons away. FDA's 2013 decision summary for Abbott's FreeStyle Precision Pro system walks through the glucose side. Glucose dehydrogenase oxidizes glucose and passes the electrons to the cofactor NAD+ (nicotinamide adenine dinucleotide), which becomes NADH. A mediator called 1,10-phenanthroline quinone takes the electrons from NADH and delivers them to the electrode, and the meter converts the resulting current into a glucose number [1].

The ketone strip works the same way, FDA says, with a different enzyme. Hydroxybutyrate dehydrogenase (HBDH) reacts with beta-hydroxybutyrate (BHB), the ketone body the strip reports [1]. Abbott's 2006 summary for its blood ketone strips calls the design an amperometric biosensor, meaning it measures an electrical current, and that current is proportional to the BHB in the sample [3]. The enzyme route matters because the older color test for ketones, the nitroprusside reaction used on urine strips, can't measure BHB at all [4].

Here's what surprised us: the two reactions don't finish together. The Precision Pro meter shows glucose after a 5-second countdown and BHB after 10 seconds [1]. Other designs get from NADH to the electrode by a different path. One LifeScan patent gives, as an example ketone reagent, HBDH and NAD paired with diaphorase, an enzyme that moves electrons from NADH to a ferricyanide mediator [5].

How systems keep the reactions apart

If two NAD-based reactions shared one electrode, the meter couldn't tell which current came from glucose and which from BHB. The systems and patents we read handle that in three ways.

Separate strips, one meter

The simplest answer is a strip for each analyte. FDA cleared MediSense's Precision Xtra system in July 1999 with Precision blood glucose strips and separate Precision Xtra beta-ketone strips [6]. The FreeStyle Precision Pro follows the same plan: every strip is single-use, and scanning the bar code on each strip's foil packet calibrates the meter for that lot [1]. The ketone strip in that 2013 clearance wasn't new, either; FDA notes it is the unchanged Precision Xtra blood beta-ketone strip under a new brand name [1].

Two electrodes on one strip

Putting both chemistries on a single strip is something we found mainly in patent records. LifeScan Scotland's US patent 8,323,467, granted in 2012, claims a "dual chamber" strip with two sample chambers built in stacked layers, each with its own working electrode and its own reagent layer [5]. Roche Diabetes Care's US patent 11,230,727, granted in 2022, claims a flatter layout. Two working electrodes carry different mediators but share one counter electrode, and the two measurements use different mediator concentrations and applied voltages [7]. Its examples include cross-talk tests, in which strips were dosed with samples containing both 3-hydroxybutyrate and glucose to check whether one signal leaked into the other [7]. A patent shows what a company claimed, not that a product on the shelf uses it.

Pads and membranes for lipids

Lipid panels separate their reactions by layout. Polymer Technology Systems (PTS) first had cholesterol, HDL cholesterol and triglyceride tests cleared as three separate strips; in November 2002, FDA cleared its Lipid Panel strip, which puts all three on one [2]. Membranes on the strip first separate out the red blood cells, then let plasma flow on to the reaction membrane, where it changes color [2]. A later FDA review describes three sets of dry reagents, one per analyte. One drop of blood flows sideways to reach each set, and the analyzer reads each color by reflectance, which means measuring how much light the pad reflects [8].

Each pad runs a short chain of enzymes. In the standard enzymatic cholesterol method, cholesterol esterase frees cholesterol from its esters, and cholesterol oxidase then oxidizes it, producing hydrogen peroxide that peroxidase uses to drive a measurable reaction [9]. An example reaction membrane in a PTS patent lists cholesterol esterase, cholesterol oxidase and peroxidase together with 4-aminoantipyrine, a dye precursor [10]. Triglycerides take more steps. In the colorimetric lab method published in 1982, lipase releases glycerol; glycerol kinase and glycerol-phosphate oxidase then process it in a reaction that generates hydrogen peroxide, and peroxidase turns that peroxide into color [11].

HDL is the tricky one, because the cholesterol reagents also react with LDL and VLDL. The same PTS patent describes a second layer, impregnated with phosphotungstic acid, that precipitates and holds back those non-HDL particles so the reaction layer sees only HDL cholesterol [10].

Interference and stability trade-offs

NAD-dependent enzymes are fragile. An Abbott patent notes that glucose dehydrogenase, HBDH and lactate dehydrogenase are irreversibly inhibited by compounds that react with thiol groups, the sulfur-containing groups in their active sites. It describes mediators chosen to avoid that reaction and names 1,10-phenanthroline quinone among its example quinones [12]. Roche's multi-analyte patent attacks stability from another angle. It claims a reagent in which one enzyme is covalently or ionically bonded to its coenzyme, and it describes mutant enzymes with better thermal and hydrolytic stability [7].

A 2026 laboratory study paired NAD-dependent HBDH with new phenazine-based mediators on a screen-printed strip. The strips performed consistently after five days at 60 °C, and glucose, uric acid, ascorbic acid, lactic acid and creatinine at clinically relevant levels shifted results by less than 15% [13]. That is a research prototype, not a cleared product.

Every chemistry also brings its own interference list. FreeStyle Precision Pro glucose strip labeling warns that ascorbate (vitamin C) at 2.5 mg/dL or more and xylose at 50 mg/dL or more may affect accuracy, and those strips come sealed in individual foil packets with an 18-month shelf life [1]. Abbott's 2006 ketone strip testing covered interference, oxygen sensitivity, hematocrit and environmental conditions [3]. On the lipid side, CardioChek labeling says acetaminophen and dopamine may raise glucose results. In its testing, dopamine and methyldopa lowered HDL results. The same labeling warns about very high doses of vitamin C (lower HDL) and grossly lipemic, or very fatty, samples [14].

A second analyte doesn't come free. Each one adds an enzyme to keep stable and its own caveats in the package insert. What any reading means for treatment is a decision for your care team.