# How does a glucometer work? **URL:** \ **Category:** Factual Questions\ **Created:** [August 10, 2005, 9:25pm UTC](https://boards.straightdope.com/t/how-does-a-glucometer-work/316508 "2005-08-10T21:25:20Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 10, 2005, 9:25pm UTC](https://boards.straightdope.com/t/how-does-a-glucometer-work/316508/1 "2005-08-10T21:25:20Z")
I assume a glucometer measures the electrical resistance of a low current passed through a drop of blood. And, it equates that amount of resistance (or conductivity) to an amount of sugar in the blood. Is this correct? If so, there aren’t there other electolytes in the blood which would affect the conductivity or resistivity of the blood? How can it be “tuned-into” just glucose? - Jinx ---
**Author:** ![Nunavut\_Boy](https://avatars.discourse-cdn.com/v4/letter/n/e95f7d/32.png) [@Nunavut\_Boy](https://boards.straightdope.com/u/Nunavut_Boy)\ **Post date:** [August 10, 2005, 9:34pm UTC](https://boards.straightdope.com/t/how-does-a-glucometer-work/316508/2 "2005-08-10T21:34:26Z")
I believe most of the are photometric, just like the big boy analyzers in the lab (except less complicated). A reagent strip impregnated with some chemicals will change color when glucose is added. The color change is directly proportional to the concentration of glucose in the sample. This color change is measured via reflectance. I’m going back to work in a little bit, I’ll check the product insert for the glucose meter we have in our lab. Then you’ll know more than you wanted to about glucose assays! ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [August 10, 2005, 9:36pm UTC](https://boards.straightdope.com/t/how-does-a-glucometer-work/316508/3 "2005-08-10T21:36:17Z")
Fascinating! Yeah, I’d like to hear more about this. ---
**Author:** ![Cleophus](https://avatars.discourse-cdn.com/v4/letter/c/a88e57/32.png) [@Cleophus](https://boards.straightdope.com/u/Cleophus)\ **Post date:** [August 10, 2005, 9:59pm UTC](https://boards.straightdope.com/t/how-does-a-glucometer-work/316508/4 "2005-08-10T21:59:05Z")
> [@Jinx](#): > > I assume a glucometer measures the electrical resistance of a low current passed through a drop of blood. And, it equates that amount of resistance (or conductivity) to an amount of sugar in the blood. Is this correct? > > If so, there aren’t there other electolytes in the blood which would affect the conductivity or resistivity of the blood? How can it be “tuned-into” just glucose? > > - Jinx That’s not quite how it works. There are two types of sensor used in common glucometers. The first type, as Nunavaut Boy mentioned, is a reflectance sensor. The reagent in the test strip oxidizes the sample, causing a color change in the reagent that can be measured by a photosensor. This is an older technology, and generally requires more blood compared to electrochemical sensors. An insufficient sample won’t react with enough reagent to cause a detectable color change, or it will partially react and give an incorrect reading. In electrochemical sensors, the reagent in the test strip oxidizes the sample, generating an electric current. The electrical current generated is proportional to the concentration of glucose in the sample. This technology is used in the latest meters and requires less blood than reflectance meters. ---
**Author:** ![Nunavut\_Boy](https://avatars.discourse-cdn.com/v4/letter/n/e95f7d/32.png) [@Nunavut\_Boy](https://boards.straightdope.com/u/Nunavut_Boy)\ **Post date:** [August 10, 2005, 10:24pm UTC](https://boards.straightdope.com/t/how-does-a-glucometer-work/316508/5 "2005-08-10T22:24:39Z")
The insert for our glucose meter (Roche Accu-Check compact) is not very specific about what reaction is used to determine glucose conc. It does say that "a chemical reaction occurs and the test area changes color. Accu-Chek Compact registers this color change and from it calculates your blood glucose. The manual for our big analyzer (a Vitros 250, the Chevy Cavalier of clinical analyzers) has much better information. To whit: > [@Vitros 250 Methodology Manual](#): > > A drop of patient sample is depositied on the slide and is evenly distributed by the spreading layer to the underlying layers. The oxidation of sample glucose is catalyzed by glucose oxidase to form hydrogen peroxide and gluconate. This reactions is followed by an oxidative coupling catalyzed by peroxidase in the presence of dye precursors to produce a dye. The intensity of the dye is measured by reflected light at 540nm. This analyzer is pretty cool. We can do: acetaminophen, albumin, alcohol, alkaline phosphatase, alanine aminotransferase, ammonia, amylase, aspartate aminotransferase, urea, calcium, cholesterol, creatine kinase, chloride, creatinine, bilirubin, co2, iron, gamma glutamyl tranferase, glucose, HDL cholesterol, potassium, lipase, magnesium, sodium, phosphorous, total protein, salicylates, totoal iron binding capacity/% saturation, triglycerides, uric acid and others. The way you thought glucose was measured is sort of like the way electrolytes are measured (on this machine). Take two ion-selective electodes and put your patient sample on one and a reference fluid on the other. Each sample creates a voltage based on the amount of electrolyte in the sample. The difference between the patient sample and reference sample is proportional to the electrolyte concentration in the patient sample. FUN FACT: The analyzer we (and many, many labs) have used to be made by Eastman Kodak. Vitros (Johnson & Johnson) bought out Kodak’s Clinical Chemistry division sometime in the early-mid 90’s.