Tech In Plain Sight: Glucose Meters

If you or someone you know is diabetic, it is a good bet that a glucose meter is a regular fixture in your life. They are cheap and plentiful, but they are actually reasonably high tech — well, at least parts of them are.

The meters themselves don’t seem like much, but that’s misleading. A battery, a few parts, a display, and enough of a controller to do things like remember readings appears to cover it all. You wouldn’t be surprised, of course, that you can get the whole affair “on a chip.” But it turns out, the real magic is in the test strip and getting a good reading from a strip requires more metrology than you would think. A common meter requires a precise current measurement down to 10nA. The reading has to be adjusted for temperature, too. The device is surprisingly complex for something that looks like a near-disposable piece of consumer gear.

Of course, there are announcements all the time about new technology that won’t require a needle stick. So far, none of those have really caught on for one reason or another, but that, of course, could change. GlucoWatch G2, for example, was a watch that could read blood glucose, but — apparently — was unable to cope with perspiration.

Even the meters that continuously monitor still work in more or less the same way as the cheap meters. As Hackaday’s Dan Maloney detailed a few years back, continuous glucose monitors leave a tiny sensor under your skin and measure fluid in your body, not necessarily blood. But the way the sensor works is usually the same.

For the purposes of this article, I’m only going to talk about the traditional meter: you insert a test strip, prick your finger, and let the test strip soak up a little bit of blood.

Two Different Kinds

Glucose meter
Typical inexpensive glucose meter

However you slice it, the real magic is in the test strips. However, how you measure the strip can vary. By far the most common way is to use an amplifier to read the very small currents. However, you can also use precise LEDs and a photodiode — this also requires a very precise current reading, an extra chemical, and precise timing, so you don’t see optical-based meters very often today. The exception is that there are test strips that you can read by simply looking at the color of the strip. This isn’t very accurate, but it is inexpensive and convenient. For most people, the exact blood sugar reading isn’t necessarily as important as knowing if it is normal, high, or very high, for example, so eyeballing the color off a strip is sometimes adequate.

The usual test strip uses a chemical to react to the blood sample. Each strip type can be different, using a different chemical reaction or a different number of electrodes. However, there are a few common elements.

First, the strip will use some sort of enzyme that will react with the glucose in the sample and produce something you can detect electronically. Glucose oxidase is the most common choice, although there are other similar enzymes like glucose dehydrogenase nicotinamide adenine dinucleotide or glucose dehydrogenase flavin adenine dinucleotide.

The picture below shows two different brands of strips with and without the covers that hide all the workings. Blood enters on the left and the right side has contacts that connect to the meter.

Test strips
The top and bottom test strips have had their internal structure exposed.

If you have to stick your finger with a needle several times a day, you get pretty sensitized to how big that needle is. Over time, blood glucose meters have become more and more sensitive so they require less blood. Less blood means you can use a thinner needle and maybe not set it to go so deep. Anything that can reduce the amount of blood required per test is going to help sell meters to patients. A state-of-the-art meter today might use as little as 300 picoliters of blood. A hungry mosquito will take about 10 microliters, so 300 picoliters is a very tiny amount indeed. In general, capillary action draws a known amount of blood into the strip after you stick your finger.

Cells

A strip may have more than one cell for different purposes. For example, one cell may simply detect that blood arrived at the location, implying that the previous cell should offer a valid reading. Each cell will have at least a pair of electrodes. In some cases, a cell will have more than two electrodes and, in that case, the meter will apply a bias current to one electrode. This increases complexity but can provide a better result.

Some meters elect to measure the total electric charge produced by the chemical reaction. Others measure the charge at a particular time in the reaction and use that to deduce the total.

The test strips, by the way, are where all the money is made since they are disposable. Just like Radio Shack used to give away flashlights to sell batteries, glucose meters are often given away free or sold at very low prices, knowing that you will then need to buy a steady supply of strips to make the meter useful.

Coding

Most meters today don’t require coding, but this was common in the past. Different batches of test strips would have different characteristics, so you’d need to enter a code from the strips into the meter to get accurate readings. If you are hardcore, you can also get calibration solutions to test the accuracy of the meter.

Some meters will use test strips that communicate their code to the meter automatically. This might be via some mechanism on the strip or in the container used for a container of strips. While some test strips may have a cell dedicated to calibration, most strips are now simply produced to a tight tolerance so that the coding can be easily automated by either using a single calibration constant or by detecting one of a few constants using a simple connection on the strip.

High Tech Everywhere

The technology behind these sensors is relatively recent. The original work dates back to the late 1950s with practical sensors similar to what you see today showing up in the early 1960s. However, the amount of blood required, the accuracy, and — of course — all the microcontroller whiz-bang features have improved over the last half a dozen decades. It is amazing, though, that even after this many years, there hasn’t been a better way found to noninvasively measure blood glucose.

If I asked you to go to the drugstore and pick up a nanoammeter, you probably wouldn’t have guessed to go to the diabetic testing section. I am somewhat surprised we don’t see more of these meters — or the chips made to drive them — hacked into other instruments although we have seen at least one repurpose some of the electrochemical circuitry. Meanwhile, we are still waiting for the noninvasive glucose monitoring system we keep hearing about.

26 thoughts on “Tech In Plain Sight: Glucose Meters

  1. The test strips now cost approximately $1.00 each; they are a cash cow just as is the insulin. My endocrinologist claims they are a whopping +- 20% accurate. Any attempt to break into this monopoly will be repelled…

    1. I’ve looked into non-invasive reading of glucose, and it’s a tremendously hard problem. Glucose is such a small component of blood that reading the concentration through the skin and blood vessels is nigh impossible. Variations in skin tone, sweat, blood pressure (making blood vessels dilate) and all sorts of other issues.

      I *suspect* that it would be easier to measure glucose from blood flow in the eardrum, using an earpiece. Some IR emitter and camera to pick out the blood vessels, with an appropriate IR emitter and sensor selective for glucose.

      Technology wasn’t advanced enough to test this at the time (15 years ago – raspberry pi’s weren’t a thing), but nowadays it might be much easier. You can get leds and sensors for of specific frequencies pretty cheap, and a RasPi camera might let you selectively find and measure the blood vessels.

      (We also looked into measuring tears, from inside nostrils, and retinal blood through the eyes.)

      If anyone’s looking for an interesting avenue of hacker research: what sorts of medical things *can* you measure using an earpiece looking at the eardrum?

    2. More like $0.20 each – Walmart’s ReliOn (store brand diabetic supplies pretty much) are $19.88 per 100 strips

      At one point when I was on lesser insurance, the Walmart test strips were cheaper than the copay on “formulary” strips through insurance. Now when it comes to gouging and cash cows, this one was a doozy – insurance would charge you big $$$$$$$ copays for name-brand medications – but would also declare that they would only cover one manufacturer’s name-brand testing supplies!!!!

      I normally don’t like cheering on Walmart, but between Walmart and the likes of Novo Nordisk/Lifescan/etc – I thank Walmart for giving the gougers a bit of a smackdown.

      I have less awful insurance now, but it’s still about the same price to just buy strips at Wally World.

      1. Sadly it’s all about money. PBMs will direct you to on-brand on-formulary drugs because they get rebates (basically legal kickbacks for medication steering) which is why brand has gotten more popular than generics with PBMs (the entity that typically manages your drug benefit).

        While it seems Walmart is giving them a smackdown, they’re just pulling rebates the same way. In this case, their pharmacy gets a market share rebate for pushing Novo Nordisk’s products. Except, it’s not their pharmacy pushing it (that’d be medication steering), rather it’s a separate entity of Walmart providing basically a discount benefit.

        Drug pricing is a pain in the ass. Pharma can be greedy, but PBMs are geedy-er. Take a look at the Drug Channels blog, specifically the gross-to-net bubble. It talks about a lot of these kind of moves. Been in Pharmacy for 20+ years, the tricks these companies will play never surprise me anymore.

      2. … sort of? Sadly, the strips are all specific to their model of meter- I have both a ReLion and ReLion Prime meter (both from the Mart of Wal) and they used different strips.

        I will state that the smart meters are a joke- they are landfill quality android phones at the core with most of the phone functionality (and UI) stripped out and just the meter software installed. I still have doubts about what they do with the data that’s sent up to them (you can’t opt out of it- they will actively contact you if the meter doesn’t phone home in a certain time frame, and the meter’s ‘airplane’ mode will only hold so many readings), and for me at least it’s pointless because my PCP actively refused to have the readings sent to them.

    3. Yes, I came here to point out that these meters are like inkjet printers – the hardware is dirt cheap but the cost of the consumables is brutal. But unlike printers ink, there are no cheap third-party test strip substitutes and no way to “refill” them.

        1. High Blood sugar kills you over a long period, relatively. Low blood sugar can kill you in an hours time but may have body warnings. I just need to avoid the edges and be somewhere in the middle of normal so being off 20 points is not a consequence

          I hate Wallyworld, but the prime strips at $ 17.67 @ hundred are 1/2 the price of everything else and nobody has a reduced price for financially challenged people

        2. It amazes me how risk averse the average person is, never knew it till the pandemic hit. I would say off the top of my head maybe a 5% increase in my chance of getting killed would make me change my behavior might be more like 10 to 15%. Somehow I’ve made it 41 years so far.

          Yes I would “risk” my health to save $1,000’s of dollars. any people take much bigger risks for a lot less without even realising it all the time. Plus if your checking your sugar levels chances are you’ve been “risking” your health for quite some time already.

          1. Im 70, didnt have this “risk” at 40. 55 is when it (discovered during routine blood testing) began to rear it’s ugly head. So far there is no cure, just a slow decay until a side effect kills me, maybe in another 20 years or so.

    4. The human body is like a big capacitor, sugar levels will change the body capacitance.
      Wet contacts on each wrist could go to a circuit to measure capacitance precisely.
      A simple 555 timer will change output frequency if the body capacitance is coupled into the RC circuit.
      Frequency to voltage converter, and hey presto!
      Peace !

  2. Looked into this too.
    The company that figures this out will be worth hundreds of billions of dollars within a year.
    Interestingly SpO2 meters also used to be quite complicated but have been reduced to a single monolithic component containing signal processing and conditioning components so an earpiece monitor is a promising option.
    I did find out that one intriguing approach is looking at other non-glucose components which can be correlated, such as ketones though this would only work as an alert to a dangerous situation and not for general use.
    Correlating multiple sensors using DL might be a potential option, as a global change in several key wavelengths could be enough now we have single mode laser diodes throughout the visible and infrared spectrum.

    1. First of all, I’m not arguing your point…
      B^)
      “Interestingly SpO2 meters also used to be quite complicated but have been reduced to a single monolithic component containing signal processing and conditioning components so an earpiece monitor is a promising option”

      Last year I bought a $10 SpO2 fingertip meter from Banggood.com, (now it is around $16), and it has served us well for in-home testing.

      My wife, a Critical Care Nurse, keeps it in her Medical Bug-Out Bag.

  3. FWIW, the ISO standard (ISO15197-2013, “In vitro diagnostic test systems – requirements for blood-glucose monitoring systems for self-testing in managing diabetes mellitus”) is +/- 15% above 100 mg/dL and +/- 15 mg/dL below that, which, as you note, can be well over +/- 20%! Turns out this is good enough for most diabetes management, but still scary if you assume the readings are much more accurate.

    Reliable test strips can be had for about $0.30/ea in the US via big retailers (see: Arkray-made Wal-Mart-branded ReliOn Confirm/Micro testers) when they’re in stock, which is always the problem. For the most recent run-down on which testers are good and which suck: https://www.diabetestechnology.org/surveillance.shtml

    and maybe worth looking at the 2012 report which originally kicked off all the (righteous) concern about just how bad some meters and strips were: https://pubmed.ncbi.nlm.nih.gov/23063032/

  4. Putting my hand up to say how much I’m loving this Tech Hidden In Plain Sight series. It’s funny how sometimes the most common day-to-day stuff can be both seemingly simple yet deceptively complex (a triumph of successful design) yet also the knowledge feel more inaccessible than more obviously complex tech.

  5. A lot has happened since the 2018 CGM article referenced in this article was written. I switched to a FreeStyle Libre CGM sensor and the system works great. I apply a new sensor every 15 days and then just monitor my food intake, glucose level and insulin.

  6. I have been a biomed since the early 80’s. If you have discovered and perfected a way to easily and effectively measure glucose levels you will have saved lives and become rich. Here is a money train the sleazy will be following… the more of us competent following the field the more lives will be saved by us knocking out the sleaze that infect the world. YOUR HEAD MAKES A DIFFERENCE.

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