Continuous Glucose Monitoring (CGM)Explained: Accuracy, Eligibility, and Key Benefits

What Is Continuous Glucose Monitoring?

Continuous glucose monitoring (CGM) refers to a medical system that measures glucose levels in the interstitial fluid (just below the skin) at regular intervals—typically every 5 to 15 minutes—and transmits that data to a receiver, smartphone, or insulin pump. Unlike traditional fingerstick blood glucose tests (which provide discrete snapshots), CGM provides a dynamic, continuous glucose profile, enabling users and clinicians to observe trends, detect excursions, and respond proactively.

A CGM system typically consists of three parts:

• Sensor (inserted under the skin)
• Transmitter (sends the data)
• Receiver or display device / app

In many clinical guidelines (for example, ADA / Standards of Care), CGM is increasingly recommended for people with type 1 diabetes, and for many with type 2 diabetes who require insulin or have frequent glycemic variability.

How Accurate Is Continuous Glucose Monitoring?

Accuracy is a major concern for users and clinicians. Let’s review what the literature says:

• A meta-study of 22 trials (n = 2294 patients) showed that the average Mean Absolute Relative Difference (MARD) across currently available CGM devices was 9.4%. While devices are reasonably accurate in euglycemia and hyperglycemia ranges, their performance in hypoglycemia is still less robust (sensitivity ≈ 85.7%, specificity ≈ 95.3%). PubMed
• In a real‐world hospital/clinical setting, CGM measurements compared with lab or point-of-care glucose references showed satisfactory agreement overall, but caution remains in fast-changing glucose conditions. 
• In a reproducibility study over multiple days, sensors demonstrated better accuracy during normal and high glucose ranges than in hypoglycemic ranges. For example, MARD ~ 7.8% in 70–180 mg/dL range; when glucose <70 mg/dL, error rates could be higher. Nature
• For a 14-day CGM system (FreeStyle Libre 3), authors reported a MARD of 7.8%, with ~93.4% of readings falling within ±20 mg/dL or ±20% of the venous reference in participants aged ≥ 6 years. SpringerLink

Interpretation & caveats:

• A MARD of ~7–10% is considered quite good in the field; many regulatory and clinical decisions now rely on CGM data without confirmatory fingersticks in stable ranges.
• Accuracy tends to decrease during times of rapid glucose change (rising/falling) and in low glucose (hypo) zones.
• Calibration, sensor lag time, and patient physiology can influence performance.
• Users should understand the limitations (especially in hypoglycemia) and use CGM data alongside clinical judgment.

Thus, while CGM is not perfect, its accuracy is generally sufficient to guide therapy decisions in many contexts.

Who Qualifies for Continuous Glucose Monitoring?

Eligibility and guidelines vary by region, insurance, and clinical judgment. Below is a summary based on U.S. (Medicare, ADA) and broader diabetes-care guidance:

Clinical / Guideline-Based Eligibility

ADA 2025 Standards endorse CGM use for all individuals with type 1 diabetes and for many with type 2 diabetes who use insulin. ADCES+1

In some cases, even non–insulin-dependent patients with frequent hypoglycemia or high glycemic variability may benefit. ADCES

Insurance / Medicare Criteria (U.S. example)

As of recent changes, Medicare now allows broader CGM coverage: patients do not necessarily need a minimum insulin dose; those with documented problematic hypoglycemia may also qualify even if not on insulin. diabetes.org+1

Requirements often include: a diabetes diagnosis, a prescription, evidence of training, and periodic follow-up visits. diabetes.org+2aafp.org+2

CGM devices classified as durable medical equipment (DME) must meet specific criteria (e.g., include a standalone receiver or integration) to be covered under Medicare. 

In other countries, eligibility depends on national health guidelines or reimbursement policies.

What Are the Benefits of Continuous Glucose Monitoring?

CGM offers multiple clinical, behavioral, and quality-of-life advantages over traditional self-monitoring of blood glucose (SMBG). Key benefits include:

1.Better Glycemic Control & HbA1c Reduction

In randomized controlled trials and meta-analyses, CGM use has been associated with HbA1c reductions of ~0.3–0.5% compared to fingerstick monitoring.

Because CGM reveals trends and excursions, users can make better-informed adjustments to insulin, diet, or lifestyle.

2.Increased Time in Range (TIR)

Time in Range (e.g. 70–180 mg/dL) is now a key metric in diabetes care. CGM users often see substantial increases in TIR, which correlates with reduced risk of complications.

For instance, in a Medicare trial, TIR improved from ~43% (fingerstick) to ~59% with CGM over 8 months. diabetes.org

3.Reduced Hypoglycemia & Hyperglycemia Events

Many CGM devices support alerts/alarms for high or low glucose, helping users respond before levels become dangerous.

Observational and controlled studies show reductions in the duration and severity of hypoglycemic episodes (though detection in severe hypoglycemia remains a challenge due to sensor limitations).

4.Enhanced Patient Engagement & Behavior Change

Users gain immediate feedback on how meals, exercise, stress, or medication changes influence glucose.

This real-time insight often leads to more proactive and precise self-management.

Psychological benefits: lower anxiety, fewer fingersticks, improved confidence in diabetes control.

5.Long-Term Health Protection

Better glycemic control and more stable glucose patterns may translate to lower risks of complications (retinopathy, nephropathy, neuropathy, cardiovascular issues) over time—as suggested by long-term diabetes outcome studies.

CGM helps detect patterns that would be missed with periodic testing, enabling earlier intervention.

Real-World Example & Summary

Example Scenario

A person with type 1 diabetes uses CGM to monitor glucose trends throughout the day. Without a secure adhesive patch, the sensor may loosen during a workout or shower, causing data interruption. With your medical-grade CGM Patch, the sensor stays affixed, ensuring continuous, reliable readings for the full 10–14 day period. This continuous data supports better decision-making, more stability in glucose levels, and fewer emergency events.

Summary of Benefits

• Continuous data rather than snapshots
• Better HbA1c and glycemic control
• Increased Time in Range
• Reduced episodes of hypo-/hyperglycemia
• Better patient engagement, confidence, and quality of life
• Potential long-term reduction in diabetes complications

And, when paired with a high-quality adhesive patch, the practical barriers to use (adhesion, skin irritation, sensor loss) are minimized, so users can fully benefit from CGM.