According to scientific research, monitoring blood glucose and ketone levels can result in measurably better health outcomes for people who are overweight or who have diabetes or metabolic syndrome.
But if you want to start keeping track of your metabolic health, you’ll have to decide between several different types of monitoring devices available on the market.
Two of the most popular systems today are continuous glucose monitors (CGMs) and blood glucose-ketone meters.
This guide has all the information you need to make an informed decision on which one is right for you, including explanations of how each system works, which one is the most accurate, cost comparisons, and peer-reviewed research on treatment outcomes.
How Continuous Glucose Monitors Work: Pros and Cons
Continuous glucose monitors (CGMs) are a relatively new technology, first approved by the FDA in 1999, that allow users to receive frequent updates on their blood glucose levels.
The technology consists of a tiny implantable sensor, a connected transmitter, and a wireless receiver.
The CGM sensor is inserted under the user’s skin, typically in the upper arm or belly area, where it measures glucose levels in interstitial fluid (the fluid found in tissues between cells) every few minutes.
The transmitter communicates wirelessly with the receiver to provide data from the sensor, which then allows the user to review glucose data on the receiver readout. In some cases, the receiver can be replaced with a compatible smartphone.
The most popular CGM systems currently in use are the Dexcom G6, the Abbott Freestyle Libre, and the Medtronic Guardian Sensor 3. Most models automatically measure glucose levels every 5 minutes for a total of 288 readings per day.
Although it’s sometimes said that CGMs provide “real-time” updates on glucose levels, this is not quite correct. There’s about a 20 minute delay vs blood glucose for readings from interstitial fluids, which makes them less helpful for treatment decisions compared to finger stick glucometers (or glucose-ketone meters).
And because CGMs use interstitial fluid rather than blood to determine glucose levels, they’re also less accurate compared to blood glucose meters.
It’s extremely important for people with type 1 diabetes to understand that CGMs should not replace finger stick glucose meters. The National Institutes of Health and other diabetes management experts recommend using finger stick glucose readings to confirm treatment decisions (such as administering insulin), double-check CGM results whenever necessary, and take readings at least twice per day to calibrate CGMs.
Who Should Use Continuous Glucose Monitors?
While research into the use of continuous glucose monitoring for people with type 2 diabetes is ongoing, most people who use CGMs today have type 1 diabetes.
Some patients feel that CGMs are easier or more convenient, but current research suggests that continuous monitoring does not result in better outcomes for diabetic patients compared to frequent self-monitoring of blood glucose using a finger stick glucometer.
Pros of Continuous Glucose Monitoring
- CGMs make it easy to establish trends: Establishing glucose trends over time allows people with diabetes to learn a lot about how their meals, medications, and lifestyle decisions affect their health. While it’s also easy to do this with glucose meters or glucose-ketone meters, the automatic and frequent nature of CGM readings makes establishing trends automatic, too.
- Measures time in range: Time in range is the amount of time a person spends in the target blood sugar range — typically between 70 and 180 mg/dL — compared to the time the times they’ve been high (hyperglycemia) or low (hypoglycemia). This data is helpful in finding out which types of foods and what activity level causes blood sugar to rise and fall. The more time a person spends in range, the less likely they are to develop certain diabetes complications.
- Fewer finger sticks and easier for some users: Although CGMs shouldn’t completely replace finger stick glucose readings, some users rely on them to decrease the number of finger pricks required. They may also be easier or more agreeable for young children or people with cognitive impairment or sensory issues (at least if someone else helps set the equipment up).
- There may be fewer supplies to keep up with: For some users, continuous glucose monitors may cut down on supplies patients need to keep track of (such as lancets and glucose strips), though this isn’t entirely the case. (For example, most CGM sensors need to be replaced every 3-7 days at a cost of around $50.)
- CGMs paired with an insulin pump are convenient for some patients: This combination, also called a sensor-augmented pump, works well for some patients with type 1 diabetes. You can ask your physician if this type of device would suit your needs.
Cons of Continuous Glucose Monitoring
- Cost and affordability: CGMs require a prescription, and most people can expect to pay over $1000 up front for a continuous glucose monitoring system, then as much as $300-450 per month for supplies (the sensors, which may need to be replaced every 3-7 days, cost approximately $50). Costs may be lower depending on your health insurance and coverage.
- No ketone readings: There are currently no CGMs that measure ketone levels, which means they can’t be used to confirm a state of ketosis on the ketogenic diet. They also can’t warn people with diabetes when dangerous ketoacidosis may be occurring.
- Safety issues and side-effects: It’s not uncommon for sensors to fall off particularly in hot weather or if sweating while exercising. Sensors can also fail or lose transmission. Skin irritation or rashes can also occur.
- Most continuous glucose monitors aren’t FDA-approved for treatment decisions: Instead of relying on CGMs for medication decisions, experts recommend confirming the CGM reading first using a finger stick glucose reading before proceeding.
- CGMs are relatively inaccurate: Compared to glucose-ketone meters or glucometers, which measure capillary blood glucose, the interstitial glucose reading is inherently less accurate. Sweating or movement, especially during exercise or sports, can further reduce reading accuracy or prevent CGMs from working altogether.
- CGMs don’t provide real-time readings: CGM readings may be delayed by up to 20 minutes compared to actual blood glucose levels. Because finger stick readings don’t have this lag issue, they’re much more reliable for decision-making purposes.
- CGMs don’t replace finger sticks: You still need finger pricks if you use a CGM — according to the National Institutes of Health, experts recommend using finger prick readings twice daily to calibrate CGMs. They’re also required to confirm any treatment decision, and to double-check the CGM readings whenever necessary.
How Glucose & Ketone Meters Work: Pros and Cons
This style of meter works by analyzing a very small blood sample taken from your fingertip (also called a finger stick or finger prick) and sending an electrical current through the sample to test its resistance.
Based on the electrical resistance of a sample, the meter is then able to determine blood glucose levels in real-time within 15% accuracy (and sometimes greater accuracy), which the FDA deems to be sufficiently accurate for blood glucose management decisions for people with diabetes.
The process of measuring blood ketone levels works on the same principles as testing blood glucose, and combination glucose-ketone meters must also meet the same FDA-mandated accuracy standards for ketone testing.
After taking a blood test, the glucose or ketone reading is available for review in 10 seconds or less. The latest meter technology allows users to review their glucose and ketone data on the meter readout, on their paired devices using an app, and on a secure cloud interface.
Who Should Use Glucose-Ketone Meters?
Most people who use glucose-ketone meters fall into one or more of the following categories:
- Using the meter to manage diabetes or metabolic syndrome,
- Following the low-carb, high-fat ketogenic diet, or
- Improving metabolic health by learning how their diet and specific foods affects blood glucose and ketone levels.
As an illustration of the considerable benefits of using glucose-ketone monitors for metabolic health, a two-year clinical trial conducted by diabetes reversal pioneers Virta Health provides excellent insight.
In the study, 359 patients with type 2 diabetes enrolled to either follow the ketogenic diet with remote monitoring or usual care for people with diabetes.
The results were unprecedented: at the two-year mark, over half of patients in the monitored keto group had completely reversed type 2 diabetes, two-thirds discontinued all of their diabetes prescriptions, and the group had an 81% average decrease in insulin dosage.
But people without diabetes can also benefit from blood glucose-ketone monitoring.
Research demonstrates that the ketogenic diet is highly effective for weight loss and offers other significant health benefits. And monitoring your ketone levels ensures you’re actually in a state of ketosis, which is necessary to achieve the full benefits of keto.
Even if you’re not on the keto diet, healthy glycemic control (keeping blood sugar toward the bottom of the healthy range) is correlated with a lower risk of diabetes, greater longevity, less risk of gaining unwanted weight, and a healthier metabolism. That’s why athletes and health enthusiasts often monitor their glucose levels.
Pros of Glucose-Ketone Meters
- Accuracy: All glucose meters must meet FDA 510k standards for accurately monitoring glucose levels, meaning a high degree of accuracy is guaranteed. Glucose-ketone meters must also be FDA-approved for accuracy, which is not the case for standalone ketone meters. (Learn more about the accuracy of Keto-Mojo’s meters and how they compare to other glucose-ketone meters here.)
- Affordability: At around $45 for the meter and less than $15 for a week’s worth of strips (with twice daily testing of both glucose and ketones), glucose-ketone monitoring is much more economical than continuous glucose monitors (typically between $1000-$2000, with ongoing costs of up to several hundred dollars per month).
- For people on the ketogenic diet, monitoring blood ketone levels is the only accurate way to confirm you’re in a state of ketosis, which is required to achieve the full health and weight loss benefits of keto.
- Glucose-ketone monitors allow remote patient monitoring of diet and metabolic health by healthcare providers, which is useful for people who are overweight or obese, have diabetes, or are using a therapeutic keto diet strategy for conditions like epilepsy, cancer, or dementia.
- For people with diabetes, monitoring blood ketone levels provides an early warning of metabolic ketoacidosis, a dangerous condition that sometimes affects people with diabetes (but not to be confused with a healthy state of ketosis).
Cons of Glucose-Ketone Meters
- Checking your glucose or ketone levels with a meter does require a “finger stick” using a lancet, a type of small, 30-gauge needle (for reference, that’s around 0.32 mm in diameter). The finger stick process is easy and close to painless, and most people of all ages (including children) have no problem with it. But it’s very important to observe hygiene procedures (such as handwashing) and to never, ever share a lancet with someone else as this may expose both of you to bloodborne pathogens.
- While glucose-ketone meters and supplies are by far the least expensive option for monitoring glucose and ketone levels, they still may not be affordable for everyone. Here are some potential solutions to this issue:
CGMs vs. Blood Meters: How to Decide
If you’re having trouble deciding between a CGM and a glucose-ketone meter, this section compares both types of devices head-to-head so you can learn which is best for your needs.
Accuracy and Safety
As we’ve already touched on a few times in this guide, interstitial glucose readings from CGMs are inherently less accurate than blood glucose readings from glucose-ketone meters.
And strong evidence also suggests that continuous glucose monitors are especially inaccurate during episodes of hypoglycemia (low blood sugar), meaning relying on CGMs during a hypoglycemic episode may increase the risk of death or serious harm.
They’re also slower, meaning they tend to lag behind your real blood glucose levels.
As a result of these shortcomings, it may not be safe to rely on a CGM all by itself for significant treatment decisions.
That’s not to say that CGMs are 100% unreliable, or that they don’t sometimes help people with glucose management. However, they’re simply not accurate enough to do the job alone.
Finally, as far as safety, CGMs have another major downside compared to glucose-ketone monitors. Because they don’t measure your blood ketone levels, they aren’t helpful for detecting metabolic ketoacidosis, a potentially fatal condition that sometimes affects people with type 1 diabetes.
WINNER: A high-quality glucose-ketone meter is the clear winner for accuracy and safety. They’re not only more accurate than any CGM, but also provide insight into ketone levels, which can alert users to ketoacidosis.
For the Keto Diet, Weight Loss, and Metabolic Health
If you follow the keto diet and want to achieve weight loss or improve your metabolic health, a glucose-ketone monitor is better suited for your goals than a CGM.
For one thing, CGMs don’t provide blood ketone readings, so they’re only showing you half of the picture of how your metabolism is working.
Therefore, CGMs aren’t as helpful as glucose-ketone meters for discovering trigger foods, and they don’t allow you to explore the interplay between glucose and ketone levels after meals.
You also can’t tell whether or not you’re in a state of ketosis using a CGM, which makes them far less useful on keto.
Finally, the amount of glucose data CGMs provide (nearly 300 readings per day) is excessive for the vast majority of people. It doesn’t guarantee better results than a few well-timed readings each day.
As we discussed in a previous section, the two-year Virta Health study demonstrated groundbreaking results using glucose-ketone meters and remote patient monitoring paired with the keto diet — with no need for continuous glucose monitoring.
WINNER: Blood glucose-ketone meters have distinct advantages over CGMs for the ketogenic diet, weight loss, and metabolic health.
For Diabetes Treatment Decisions
When it comes to making diabetes treatment decisions — such as timing or dosage of insulin or other medications — most CGMs are not FDA-approved for this use.
That’s why National Institute of Health experts advise CGM users to confirm their readings using a finger stick glucometer or other FDA-indicated device for treatment decisions.
WINNER: Glucose meters or glucose-ketone meters are more accurate and safer for making diabetes treatment decisions, and are also necessary to confirm readings from most CGM systems before proceeding with a treatment decision.
Accessibility and Affordability
Continuous glucose monitors require a prescription, making them inaccessible to the many people with metabolic health concerns who lack consistent access to quality medical care.
Even with a prescription, some insurance plans cover CGMs, but many do not. Without coverage, the annual cost to use CGMs can be over $5000.
A top-of-the-line blood glucose-ketone meter requires no prescription and costs no more than $50 regardless of insurance coverage. A one-month supply of glucose and ketone strips costs around $55 at most for twice-daily testing of both glucose-ketone levels.
In many cases, glucose-ketone monitoring systems are covered by insurance or are HSA- or FSA-eligible.
WINNER: With or without health insurance coverage, glucose-ketone meters are much more affordable and accessible than CGMs.
Simplicity and Ease of Use
At first glance, continuous glucose monitoring may appear to be simpler or easier than finger stick blood glucose readings.
But keep in mind that you still need to have a finger stick system on hand to confirm readings before taking medication; to calibrate the CGM as often as twice each day; and to rely on for backup purposes.
You can’t really get away from taking blood glucose readings, so it’s worth asking: does it truly simplify your life to use a CGM and a blood glucometer as opposed to a blood glucometer (or glucose-ketone meter) by itself?
Another factor to consider is that the CGM systems are somewhat temperamental and can be affected by movement, physical activity, and sweat.
WINNER: In some situations, such as helping a very young person or someone with disabilities manage blood glucose levels, a CGM might make things easier. But in most cases, practically speaking, a blood glucose meter or glucose-ketone meter is likely simpler and easier.
Remote Patient Monitoring and Telehealth
Remote patient monitoring has significant advantages for healthcare practitioners as well as patients.
For example, evidence suggests that remote monitoring of blood glucose may reduce the risk of adverse events and help decrease insulin resistance more compared to conventional diabetes care.
Today, most models of commercially available CGMs and glucose-ketone meters have remote patient monitoring capabilities.
However, of the two methods, remote blood glucose-ketone monitoring allows healthcare providers to obtain a better overall picture of patients’ metabolic health. And unlike CGMs, it’s also suited to incorporating low-carb or ketogenic diets for therapeutic purposes.
Combining the keto diet with remote patient monitoring has the potential to revolutionize diabetes care, as shown in the two-year Virta health study, in which 53.5% of participants achieved reversal of type 2 diabetes and an additional 17.6% achieved partial or complete diabetes remission.
WINNER: The combination of a therapeutic low-carb diet with remote glucose-ketone patient monitoring is extremely promising for ensuring patient compliance and improving metabolic health or treatment outcomes for a variety of conditions, including diabetes and obesity.
Conclusion: Test, Don’t Guess
When it comes to improving your metabolic health, managing diabetes, or losing weight, quantifying your blood glucose and ketone levels can make all the difference in the world.
While continuous glucose monitors are much more expensive, less accurate, and don’t measure ketone levels, they can sometimes be a partial solution for individuals who lack the ability or willingness to self-administer finger stick tests.
Now that you know the benefits and downsides of both types of monitoring, you’re in a better position to make an informed decision as to which method best suits your needs.
But keep in mind there’s no “one-size-fits-all” solution for metabolic health or diabetes treatment, so be sure to ask your doctor if you’re unsure.