Hunter Allen's Training and Competing with a CGM Blog

Why do some endurance athletes have higher than normal HbA1c levels

info@peakscoachinggroup.com (Hunter Allen) — Sun, 27 Jul 2025 21:58:15 GMT

Is your HbA1c higher than you think it should be?

I have spoken with many athletes and particularly endurance athletes have mentioned that their HbA1c numbers are higher than they think they should be and are continuing to creep up. Some of these athletes are starting to believe that they are becoming a borderline "pre-diabetic" with an HbA1c level of 5.7 to 6.3. How could this be happening? These are highly trained endurance athletes that eat well, are lean and very, very aerobically fit. They do full distance Triathlons, race 100 mile bike races and train intensely every week. What's going on?

I have been researching this now for 3 years and have found bits and pieces of different explanations, but nothing that definitely answers the question until a friend of mine, Joe Lavelle, who runs the Wise Athletes podcast sent me this article.

Healthspan Research Review | The Paradox of Elevated HbA1c in Elite Endurance Athletes with Optimal Metabolic Health

I can't begin to re-write or paraphrase this article in any meaningful or better way. It's just outstanding in every way. I will copy and paste their "Take Home" points below. Seriously, no one in 3 years has put this together, MAJOR kudos to Shriya Bakhshi. I highly recommend you read the entire article if you are interested in this stuff. It's excellent.

TAKE HOME POINTS

Elite Endurance Athletes May Exhibit Elevated HbA1c Despite Exceptional Metabolic Health. While HbA1c is a trusted marker of average glucose over time, its interpretation can be misleading in elite endurance athletes. These individuals often exhibit low fasting glucose, high insulin sensitivity, and strong cardiovascular fitness, yet may present with HbA1c values in the 5.6–5.8% range—levels typically associated with prediabetes. This creates a diagnostic paradox: lab markers suggest impaired glycemic control in a population that routinely demonstrates superior metabolic regulation. Understanding this mismatch requires examining physiology beyond static lab thresholds.

Longer Red Blood Cell Lifespan in Athletes Can Artificially Elevate HbA1c. HbA1c reflects the glycation of hemoglobin over the lifespan of red blood cells, which is generally assumed to be ~120 days. However, chronic endurance training can subtly extend red blood cell lifespan by reducing oxidative stress, systemic inflammation, and mechanical damage. Studies suggest these cells may persist 10–20 days longer in well-trained athletes, increasing cumulative glycation exposure without an actual increase in blood glucose levels. This can nudge HbA1c upward in the absence of metabolic dysfunction, mimicking pathology where none exists.

Cortisol and Catecholamines Can Raise Glucose Transiently—But Adaptively. Elite athletes experience frequent activation of the HPA axis during training, leading to elevated cortisol and catecholamine levels. These hormones promote glucose release through gluconeogenesis and glycogenolysis, prioritizing fuel availability for working muscles. In one study by Skoluda et al., hair cortisol concentrations in endurance athletes were significantly higher than in sedentary controls, reflecting chronic physiological stress. These repeated, adaptive glucose elevations may contribute to elevated HbA1c, even though they are performance-enhancing rather than pathological.

CGM Data Reveal Transient Glucose Spikes and Dips Outside Normal Ranges. Continuous glucose monitoring (CGM) studies in elite endurance athletes show a wide glycemic range during training and recovery. Data from the Gatorade Sports Science Exchange reveal that these individuals can spend 10–20% of their day above 140 mg/dL and 5–7% below 70 mg/dL, even in the absence of insulin resistance. For example, professional soccer players have been observed exceeding 180 mg/dL during matches, while elite cyclists training at altitude averaged 108 mg/dL with peaks near 144 mg/dL. These fluctuations are adaptive responses to training, not signs of disease.

Transient Insulin Resistance After Endurance Exercise Is Not Pathological. Following prolonged endurance activity, athletes may experience temporary reductions in insulin sensitivity, a phenomenon known as transient insulin resistance. A 2023 study demonstrated that after three hours of cycling at 65% VO₂max, athletes showed impaired glucose tolerance the following day on an oral glucose tolerance test (OGTT). Despite this, their resting OGTTs and fasting markers were normal. These temporary changes are part of the recovery and adaptation process and should not be mistaken for early metabolic disease.

HbA1c Alone Is Insufficient for Assessing Glycemic Health in Athletes. Given the unique physiology of endurance-trained individuals, HbA1c should not be interpreted in isolation. Athletes with slightly elevated HbA1c may simultaneously exhibit fasting glucose in the 80–90 mg/dL range, low fasting insulin (<5 μU/mL), and low HOMA-IR scores—indicators of excellent glycemic control. When these metrics are considered together, they suggest a high-functioning metabolic system rather than early-stage insulin resistance. Dynamic testing, such as CGM or OGTT, provides a more accurate picture of glucose regulation in these populations.

The “A1C Paradox” Is Not Limited to Professionals—Volume Matters. You don’t need to be an Olympian to experience this HbA1c shift. Recreational athletes who train frequently and at moderate to high intensities—such as marathoners, triathletes, and dedicated CrossFitters—can exhibit similar patterns. The determining factor is not elite status, but cumulative training load. Individuals who consistently exceed public health exercise guidelines (e.g., 150 minutes/week moderate or 75 minutes/week vigorous) may enter a physiological state where traditional glycemic markers become less reliable.

Misclassification Has Real Consequences in Longevity and Biohacking Communities. As more health-conscious individuals adopt high-volume training as a strategy to improve healthspan, the risk of misclassifying adaptive physiology as disease increases. Mistaking a mildly elevated HbA1c for prediabetes may lead to unnecessary interventions—such as carbohydrate restriction, medication, or inappropriate dietary fear. Understanding the mechanisms behind the HbA1c paradox is essential for both clinicians and patients, ensuring that lab values are interpreted through the lens of training history, physiology, and function rather than one-size-fits-all reference ranges.

Are glucose spikes bad?

info@peakscoachinggroup.com (Hunter Allen) — Fri, 13 Jun 2025 13:34:38 GMT

Should I be worried about a glucose spike?

Are Glucose Spikes Bad for Athletes? Impact on Athletic Performance

For athletes, blood glucose levels are a critical factor in optimizing performance, recovery, and endurance. Glucose, the body’s primary energy source, fuels muscles and the brain during exercise. However, glucose spikes—rapid increases in blood sugar followed by sharp drops—can disrupt energy availability, focus, and recovery. This article examines whether glucose spikes are detrimental for athletes, how they affect athletic performance, and practical strategies to manage them during training and competition. Tailored specifically for athletes, we’ll explore the science behind glucose dynamics and provide actionable tips to maintain stable energy levels for peak performance.

Understanding Glucose Spikes in Athletes

A glucose spike occurs when blood glucose levels rise sharply, often above 140–180 mg/dL (7.8–10 mmol/L) within 1–2 hours after eating, followed by a rapid drop. In athletes, spikes can be triggered by high-carbohydrate meals, energy gels, sports drinks, or stress hormones like adrenaline during competition. While glucose is essential for fueling exercise, excessive or poorly timed spikes can lead to performance issues, particularly during high-intensity or endurance activities.

For athletes, the concern isn’t just the spike itself but the subsequent crash (reactive hypoglycemic crash- Read more about this in my book), which can cause fatigue, reduced coordination, and mental fog. Stable glucose levels—ideally maintained between 70–140 mg/dL (3.9–7.8 mmol/L) during exercise—support consistent energy delivery and cognitive function.

Are Glucose Spikes Bad for Athletic Performance?

Glucose spikes aren’t inherently harmful in the short term, as athletes often rely on quick-digesting carbs to fuel performance. However, frequent or poorly managed spikes can negatively impact training and competition in several ways:

Crashes: A spike followed by a drop (below 70 mg/dL) can lead to hypoglycemia, causing weakness, shakiness, and reduced power output. Many athletes do not realize that THEY are creating these.

Impaired Focus: Rapid glucose fluctuations affect the brain, leading to poor decision-making or loss of focus in critical moments (e.g., during a race or match).

Fatigue and Recovery Issues: Repeated spikes may stress insulin response, leading to glycogen depletion and slower muscle recovery.

Gastrointestinal Distress: High-carb intake causing spikes can lead to bloating or nausea, especially during endurance events.

Long-Term Health: For athletes with or without diabetes, chronic spikes may increase inflammation or insulin resistance, though this is less immediate for performance. Although this is up for debate and what is higher for athletes, might not be a factor as we are constantly turning the glucose over, versus a sedentary person.

Conversely, controlled glucose rises (e.g., from a pre-workout snack) are beneficial, providing readily available energy. The key is timing, quantity, and type of carbohydrate to avoid excessive spikes and crashes.

Factors Influencing Glucose Spikes in Athletes

Several factors contribute to glucose spikes during athletic activities:

Carbohydrate Type and Timing: High-glycemic foods (e.g., white bread, sugary gels) cause faster spikes than low-glycemic options (e.g., UCAN Sports Nutrition , Almond butter with Eziekel bread).

Exercise Intensity: High-intensity exercise (e.g., sprints) may initially raise glucose due to adrenaline, followed by a drop, while moderate aerobic exercise lowers glucose steadily.

Adrenaline and Stress: Competitive settings or pre-event nerves can spike glucose via stress hormones, even without food intake.

Hydration and Fatigue: Dehydration or glycogen depletion can exacerbate glucose fluctuations.

Individual Differences: Athletes with diabetes or varying insulin sensitivity respond differently to carbs and exercise.

Impact on Different Types of Athletes

Endurance Athletes (e.g., Marathoners, Cyclists): Need sustained glucose availability over hours. Spikes from over-fueling can lead to crashes, reducing stamina.
Power Athletes (e.g., Weightlifters, Sprinters): Rely on short bursts of energy. Spikes may be less disruptive but can impair focus or recovery if poorly timed.
Team Sport Athletes (e.g., Soccer, Basketball): Require consistent energy and mental clarity. Spikes can disrupt performance during prolonged or intermittent high-intensity efforts.

Key Considerations for Managing Glucose Spikes

Athletes can minimize the negative effects of glucose spikes by adopting strategies tailored to their sport, body, and training demands. Below are critical considerations and practical tips to optimize glucose stability and athletic performance.

Choose Low- to Moderate-Glycemic Carbohydrates
Opt for complex carbs like UCAN Sports Nutrition products. This is what I use. Here's a discount for you. Choose whole grains, fruits, or legumes 2–3 hours before exercise to provide steady energy without sharp spikes.
During exercise, use moderate-glycemic sources like bananas or sports drinks with maltodextrin for sustained release, rather than pure glucose gels.
Example: A pre-workout meal of oatmeal with berries is less likely to cause a spike than a sugary energy bar.

Time Your Carbohydrate Intake

Consume 30–60 grams of carbs 1–2 hours before exercise to top off glycogen stores without overloading blood glucose.
For sessions over 60–90 minutes, take 30-40 grams of carbs every 30–45 minutes to maintain levels without spiking.
Post-exercise, pair carbs with protein (e.g., a smoothie with fruit and whey) within 30–60 minutes to replenish glycogen without excessive spikes.

Monitor Glucose Levels with a CGM

Use a continuous glucose monitor (CGM) during training to track real-time glucose trends, especially for athletes with diabetes or those prone to crashes.
Check glucose before, during (if feasible), and after exercise to identify patterns and adjust fueling.
Non-diabetic athletes can benefit from CGMs to fine-tune nutrition strategies.

Balance Macronutrients
Pair carbs with protein or healthy fats in pre-workout meals to slow digestion and reduce spike severity (e.g., toast with avocado and egg).
Avoid consuming carbs alone during long sessions; include small amounts of protein or fat (e.g., a nut butter packet) to stabilize glucose.

Adjust for Exercise Intensity and Duration

For high-intensity, short-duration workouts (<45 minutes), minimal carbs may be needed unless glycogen is depleted.
For endurance events, plan carb intake to match energy expenditure (e.g., 60–90 grams/hour for ultra-marathons).
Be cautious with adrenaline-driven sports; monitor for delayed crashes after competition.

Stay Hydrated

Dehydration impairs glucose regulation. Drink water or electrolyte-rich fluids (4–8 oz every 15–20 minutes during exercise).
Avoid sugary sports drinks unless carbs are needed, as they can cause unnecessary spikes.

Test and Personalize Fueling Plans

Experiment during training (not competition) to find carb types, amounts, and timing that minimize spikes for your body.
Keep a log of glucose responses, performance, and symptoms to refine your strategy.
Work with a sports dietitian to tailor plans, especially for athletes with diabetes or unique metabolic needs.

Manage Competition Stress

Practice relaxation techniques (e.g., deep breathing, visualization) to reduce adrenaline-driven glucose spikes before events.
Stick to familiar pre-competition meals to avoid unexpected glucose fluctuations.

Recover Strategically
After exercise, prioritize glycogen replenishment with a carb-protein recovery shake. Use a 2:1 -4:1 Carb: protein ratio for maximum absorption. And then eat a good, healthy plant-forward meal to stabilize glucose and support muscle repair in the next hour or two.
Monitor for delayed hypoglycemia (6–12 hours post-exercise), especially after intense or prolonged sessions, and have a snack if needed.

When Are Glucose Spikes Acceptable?

Small, medium, and even high controlled glucose rises are normal and beneficial during exercise, especially for endurance athletes needing quick energy. For example, a sports gel raising glucose to 120-180 mg/dL during a marathon can sustain performance without harm. The goal is to avoid extreme spikes (e.g., >180 mg/dL) or crashes (<70 mg/dL) that disrupt energy or focus.

Special Considerations for Athletes

Athletes with Diabetes: Must balance insulin, carbs, and exercise to prevent spikes and lows. CGMs and medical guidance are essential.
Non-Diabetic Athletes: May experience reactive hypoglycemia from over-fueling. Focus on balanced, timed nutrition.
Young or Novice Athletes: May be less aware of glucose symptoms. Education and monitoring are key.
Elite Athletes: Small glucose fluctuations can mean the difference between winning and losing. Precision fueling is critical.

Conclusion

Glucose spikes are not inherently bad for athletes but can harm performance if they lead to crashes, fatigue, or mental fog. By choosing the right carbs, timing intake, monitoring glucose, and personalizing strategies, athletes can maintain stable energy levels for optimal training and competition. Whether you’re a sprinter, marathoner, or team sport athlete, managing glucose effectively enhances endurance, focus, and recovery. Test your approach, stay consistent, and consult professionals to fine-tune your plan for peak athletic performance.

How low is too low?

info@peakscoachinggroup.com (Hunter Allen) — Fri, 13 Jun 2025 12:58:33 GMT

When should you be concerned about being too low in glucose?

How Low Is Too Low for Your Glucose Level When Exercising, Competing, or in Life?

Maintaining stable blood glucose levels is critical for overall health, particularly during physical activity, competitive sports, or even daily life. Hypoglycemia, or low blood glucose, will definitely impair physical performance, cognitive function, and, in severe cases, lead to life-threatening complications. This article explores what constitutes dangerously low glucose levels, how they affect the body during exercise or competition, and practical strategies to prevent and manage hypoglycemia. With insights grounded in medical understanding, we’ll provide key tips to help you stay safe and perform at your best.

Understanding Blood Glucose and Hypoglycemia

Blood glucose, measured in milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L), is the primary energy source for your muscles, brain, and other organs. Normal fasting (before breakfast in the morning) blood glucose levels typically range from 70–99 mg/dL (3.9–5.5 mmol/L). Hypoglycemia is generally defined as a blood glucose level below 70 mg/dL (3.9 mmol/L), though symptoms and risks vary by individual, activity level, and health status. Please note that everyone is different, and women tend to be lower than men, so women might see their glucose in the 60-70mg/dL range.

During exercise or competition, your muscles demand more glucose, which can deplete blood sugar rapidly, especially for people with diabetes or those engaging in prolonged or intense activities. In daily life, factors like fasting, stress, or medication can also lower glucose levels.

Knowing how low is "too low" depends on recognizing the thresholds where symptoms and risks emerge.

How Low Is Too Low?

Medical guidelines categorize hypoglycemia into three levels based on blood glucose readings and symptoms:

Level 1 (Mild Hypoglycemia) : Blood glucose between 54–70 mg/dL (3.0–3.9 mmol/L). Symptoms may include shakiness, sweating, or mild confusion, but individuals can often self-treat.
Level 2 (Moderate Hypoglycemia) : Blood glucose below 54 mg/dL (3.0 mmol/L). Symptoms intensify, including difficulty concentrating, irritability, or coordination issues, often requiring assistance.
Level 3 (Severe Hypoglycemia) : Blood glucose so low it causes unconsciousness, seizures, or inability to self-treat, typically below 40 mg/dL (2.2 mmol/L), though exact thresholds vary.

For athletes or those exercising, even mild hypoglycemia will impair performance, while moderate to severe levels pose serious risks. In daily life, prolonged or severe hypoglycemia can lead to neurological damage or coma if untreated.

Why Glucose Levels Drop During Exercise or Competition

Exercise increases glucose uptake by muscles, especially during aerobic activities like running or cycling, which rely heavily on blood sugar and glycogen stores. Several factors contribute to hypoglycemia risk:

Intensity and Duration : High-intensity or prolonged exercise (over 60–90 minutes) depletes glucose faster.
Insulin Resistance or Sensitivity : In people who have insulin resistance, glucose may stay up longer but then drop rapidly and somewhat unexpectedly. For those with diabetes, insulin doses or timing may not align with exercise demands, causing glucose to drop. For those with excellent insulin sensitivity, you may quickly pull the glucose out of your bloodstream and into your muscles in such a way that it drops your glucose level. In combination with working out simultaneously, you might just have the "double whammy" effect because you are so insulin sensitive.
Carbohydrate Intake : Inadequate fueling before or during activity can lead to low glucose.
Dehydration or Heat : These can exacerbate glucose fluctuations.
Stress and Adrenaline : Competitive settings may spike adrenaline, initially raising glucose but leading to a crash later.

In daily life, skipping meals, excessive alcohol, or medications like insulin or sulfonylureas can also trigger hypoglycemia, particularly in those with diabetes.

Symptoms of Low Blood Glucose (Bonking)

Recognizing hypoglycemia early is crucial. Symptoms vary but often include:

Physical: Trembling, sweating, weakness, hunger, or palpitations.
Cognitive: Confusion, difficulty focusing, irritability, or anxiety.
Neurological: Dizziness, blurred vision, or, in severe cases, seizures or unconsciousness.

During exercise, symptoms like fatigue or shakiness may be mistaken for normal exertion, making monitoring essential, especially for athletes with diabetes.

Risks of Low Glucose During Exercise or Competition

Hypoglycemia during physical activity can lead to:

Reduced Performance: Impaired muscle function and coordination.
Injury: Dizziness or confusion increases the risk of falls or accidents.
Cognitive Impairment: Poor decision-making in competitive settings.
Severe Outcomes: Seizures, loss of consciousness, or long-term neurological damage if untreated.

In daily life, untreated hypoglycemia can disrupt work, driving, or other tasks, with severe cases requiring emergency intervention.

Key Tips for Preventing and Managing Low Glucose

To maintain safe glucose levels during exercise, competition, or daily life, follow these evidence-based strategies:

Monitor Blood Glucose Regularly
Use a continuous glucose monitor (CGM) or glucometer before, during, and after exercise.
Check levels every 30–60 minutes during prolonged activity or if symptoms arise.
In daily life, test if you feel off or after potential triggers like fasting or medication.
Fuel Properly Before (Priming) and During Activity
Consume 15–30 grams of carbohydrates 10-15 MINUTES before exercise (e.g., a banana, toast, or energy gel).
For sessions lasting over an hour, take 60-90 grams of carbs every 30–60 minutes (e.g., sports drinks, gels, or dried fruit).
In daily life, avoid skipping meals and include balanced carbs, proteins, and fats to stabilize glucose.

Adjust Medications with Medical Guidance
For people with diabetes, consult your doctor to adjust insulin or oral medications before exercise or competition.
Reduce insulin doses by 20–50% for planned activity, depending on intensity and duration.
Be cautious with evening exercise, as delayed hypoglycemia can occur during sleep.

Know Your Body’s Response
Track how different activities, foods, or stressors affect your glucose levels.
Be aware that high-intensity exercise may initially raise glucose due to adrenaline, followed by a drop hours later.
In daily life, note patterns (e.g., morning lows or post-meal crashes) to anticipate risks.

Carry Fast-Acting Carbohydrates
Always have 15–30 grams of fast-acting carbs on hand, such as gels, chews or sports drink.
During exercise, keep these accessible (e.g., in a pocket or with a coach).
In daily life, carry them in your bag or car, especially if you’re prone to lows.

Treat Hypoglycemia Promptly (The 15-15 Rule)
If glucose is below 70 mg/dL or symptoms appear, consume 15 grams of fast-acting carbs (e.g., 4 oz juice or 1-2 sports gels).
Wait 15 minutes, then recheck glucose. Repeat if still below 70 mg/dL.
Once stable, eat a snack with carbs and protein (e.g., a peanut butter sandwich) to prevent recurrence.

Stay Hydrated and Manage Stress
Drink water or electrolyte-rich fluids during exercise to support glucose regulation.
In competition, practice stress management techniques like deep breathing to minimize adrenaline spikes.
In daily life, moderate alcohol and manage stress to avoid glucose fluctuations.

Plan for Post-Exercise Recovery
After exercise, make a recovery shake with a 2:1 up to a 4:1 Carb to protein ration to create a glucose spike, which in turn causes the pancreas to release insulin and then help absorb those carbs and proteins into your cells more quickly and completely.
After exercise, eat a balanced meal or snack within 1–2 hours to replenish glycogen stores.
Monitor glucose overnight, as delayed hypoglycemia is common 6–12 hours post-exercise.

When to Seek Emergency Help

If blood glucose doesn’t rise after two 15-gram carb treatments, or if symptoms worsen (e.g., confusion, seizures, or unconsciousness), seek emergency help immediately. Call 911 or administer glucagon (if prescribed) for severe hypoglycemia. During exercise or competition, stop activity and prioritize treatment.

Special Considerations

People with Diabetes: Face higher hypoglycemia risks due to insulin or medication use. CGMs and careful planning are critical.
Non-Diabetic Athletes: May experience exercise-induced hypoglycemia (reactive hypoglycemia) if under-fueled or overexerted.
Children and Elderly: Are more vulnerable to severe hypoglycemia and may need closer monitoring.
Daily Life Triggers : Stress, illness, or hormonal changes can lower glucose unexpectedly, even without exercise.

Conclusion

Understanding how low is "too low" for your glucose levels is essential for safe exercise, competition, and daily living. Blood glucose below 70 mg/dL signals mild hypoglycemia, while levels below 54 mg/dL or severe symptoms demand urgent action. You can prevent and manage low glucose by monitoring regularly, fueling appropriately, and following the key tips outlined. Whether you’re an athlete, a person with diabetes, or simply navigating life’s demands, proactive glucose management empowers you to stay healthy, safe, and at your best.

Is my CGM accurate?

info@peakscoachinggroup.com (Hunter Allen) — Wed, 11 Jun 2025 17:19:32 GMT

How do you know if your CGM is accurate?

Accuracy of your glucose values IS essential. If your CGM tells you that your glucose is 91mg/dL and your finger stick is 144mg/dL, the CGM data is essentially useless. That's a huge range and not helpful. You can imagine what you might think when you wake up in the morning and it's flip-flopped the other way! Your CGM reads 144mg/dL, and your finger stick reads 91mg/dL! If you went by your CGM, then you might think you have a glucose problem and need to see your Doctor. You want an accurate reading.

Your glucose level will be different depending on the location of the measurement.

A CGM measures your glucose in the interstitial space, and that is at the "end of the chain," so to speak, from when you ingest carbs, and the glucose moves throughout your body. Measuring with a glucometer, a finger prick will measure the actual blood glucose, but it's also in an extremity, so it's also delayed. If you are in a hospital, your blood glucose can be measured intravenously, and that's the fastest and "closest" place to measure blood glucose. For example, your intravenous measurement might be 100mg/dL, your finger stick 90mg/dL, and your CGM 80mg/dL.

What should I do to ensure I know my CGM is reading correctly? First off, you need to buy an inexpensive glucometer. You can buy these with the test strips, finger pricker, lancets for under $40 now, and I recommend testing yourself 3 hours after inserting your CGM, then again 24 hours later, and again if you have ANY doubt about the CGM reading. When you do a few tests of your finger stick blood glucose and compare it to your CGM, you will know how much difference there is between them. **IMPORTANT**>> Make sure you take your finger stick reading RIGHT after your CGM reading "updates". Some CGMs will update every 15 minutes, others every 5 minutes, and every 1 minute, so it's super important that you get your blood glucose finger stick right after your update. If your CGM hasn't updated for 14 minutes and it's reading 100mg/dL but you had (2) sports gels 10 minutes ago and your finger stick reads 150mg/dL, then do not confuse this for a bad CGM reading.

What about consistency? "Most" of the time, you won't see much variation throughout the time you have your CGM inserted, and if it's 20mg/dL high or low from your finger stick, then it will likely stay that way for the life of the CGM. The "over the counter" CGMs like Stelo and Lingo are advertised as accurate to +/- 20mg/dL, and I have found that's correct 90% of the time. I recently had a Stelo sensor that was off by 50mg/dL, and it got worse the closer it got to its end of life. I have had other sensors, such as the finger stick and the CGM, for the entire life of the CGM sensor. The prescription sensors, like the Dexcom-G7 and Abbott Labs Freestyle Libre 3, are advertised as +/- 10mg/dL, and I, too, have found this to be correct 90% of the time. For this reason, I predominantly use a Freestyle Libre 3 from Theia. (Our link lets you join our community if you purchase a sensor. Learn more here . )

If your CGM consistently differs from your finger stick, that's fine. Once you know which way it is "off," you'll be able to calculate that in your head to get a clear understanding of your finger stick blood glucose.

My reading was great, and now they are totally off, what happened?

Most of the time, this is because you bumped your CGM, which slightly lifted out of your skin and then settled back into the previous location. In most cases, this messes up your readings, so be careful when entering and exiting through doorways and taking off your shirt or workout jersey. Readings can also become inaccurate if the battery dies or starts dying early. You need to then file a claim with the CGM manufacturer, and they will replace the CGM.

In conclusion, make sure you have a glucometer and test yourself a few times. If you ever "bump" your CGM at a door entrance or when taking off your shirt, and the reading starts to appear "off," then test yourself with your glucometer. If your CGM is off by 20mg/dL and it's consistent, then not to worry; just know that your finger stick values are different.