Ideal CGM Data Set for Blood Sugar Monitoring

Core CGM Metrics for Optimal Blood Sugar Management

• The American Diabetes Association recommends that for most adults with diabetes, the ideal CGM data set should include >70% time in range (70-180 mg/dL) with <4% time below range (<70 mg/dL) and <25% time above range (>180 mg/dL), measured over at least 14 days with ≥70% active CGM wear time 1, 2
• A minimum of 14 days of CGM wear is required for reliable assessment of glycemic patterns, according to the American Diabetes Association 1, 3
• At least 70% active CGM time (approximately 10 days of data) is necessary to ensure accurate representation of glycemic status, as recommended by the American Diabetes Association 1, 2

Essential Metrics for Comprehensive Assessment

• Mean glucose provides an overall average, and the Glucose Management Indicator (GMI) is a calculated value approximating A1C, as stated by the American Diabetes Association 1, 2, 4
• Glycemic variability, with a target coefficient of variation (CV) ≤36%, is an important metric, and some studies suggest lower CV targets (<33%) provide additional protection against hypoglycemia for those on insulin or sulfonylureas, according to the American Diabetes Association 1, 5, 6

Time in Ranges (Key Targets)

• Time in Range (TIR) should be >70% of readings between 70-180 mg/dL (3.9-10.0 mmol/L), and each incremental 5% increase in TIR is associated with clinically significant benefits, as recommended by the American Diabetes Association 1, 7
• Time Below Range (TBR) should be <4% of readings for level 1 (54-69 mg/dL) and <1% of readings for level 2 (<54 mg/dL), according to the American Diabetes Association 1, 4, 7
• Time Above Range (TAR) should be <25% total time above range, with level 1 (181-250 mg/dL) being part of the total time above range and level 2 (>250 mg/dL) being minimized as much as possible, as recommended by the American Diabetes Association 1, 2, 7

Modified Targets for Special Populations

• For older adults or high-risk individuals, the American Diabetes Association recommends a TIR of >50% (≥12 hours/day) in range 70-180 mg/dL, TBR of <1% (<15 min/day) below 70 mg/dL, and TAR of <10% (<2 hours, 24 min/day) above 250 mg/dL 1, 5
• For pregnant individuals, the target range is 63-140 mg/dL (3.5-7.8 mmol/L), and specific TIR targets differ from non-pregnant individuals, as stated by the American Diabetes Association 1

Visualization and Reporting

• Standardized single-page glucose reports with visual cues, such as the Ambulatory Glucose Profile (AGP), should be used, and reports should include all 10 standardized CGM metrics for comprehensive assessment, according to the American Diabetes Association 1, 2, 3, 8

Clinical Context and Interpretation

• CGM data provides more actionable information than A1C alone, which only reflects average glucose over 2-3 months, and A1C can be affected by conditions such as anemia, hemoglobinopathies, and pregnancy, making CGM data particularly valuable, as stated by the American Diabetes Association 9

Common Pitfalls to Avoid

• Insufficient data collection, focusing only on mean glucose, ignoring glycemic variability, and setting unrealistic targets are common pitfalls to avoid in CGM data interpretation, according to the American Diabetes Association 1, 3, 5, 9

Guidelines for Adequate Data Collection and Interpretation of FreeStyle Libre Continuous Glucose Monitoring

1. Minimum Data Collection Requirements

• Wear the sensor for at least 14 consecutive days and achieve ≥70 % active sensor time (≈10 days of usable data); this threshold reflects the international consensus standard for all CGM systems【10】.
• Do not base therapeutic decisions on data sets that are shorter than 14 days or have <70 % active time, because clinical value is markedly reduced【10】.

2. Standardized Glycemic Metrics for Adults

3. Adjusted Targets for Special Populations

3.1 Older Adults / High‑Risk Individuals

• TIR > 50 % (≈12 h/day) within 70–180 mg/dL【10】
• TBR < 1 % (≈15 min/day) below 70 mg/dL【10】
• TAR < 10 % (≈2 h 24 min/day) above 250 mg/dL【10】

3.2 Pregnant Individuals (Gestational Diabetes)

• Target glucose range 63–140 mg/dL (3.5–7.8 mmol/L)【10】

4. Sensor Accuracy Across Its Lifespan & Limitations

• General Accuracy – Overall Mean Absolute Relative Difference (MARD) of 8.9 %, outperforming competing systems such as Dexcom G7 (13.6 % MARD)【10】.
• Accuracy by Sensor Age – Most accurate during days 5‑7 (MARD ≈ 7.8 %); less accurate on days 0‑1 (MARD ≈ 14.5 %) and days 13‑14 (MARD ≈ 14.7 %)【10】.

4.1 Advanced Kidney Disease

• In hemodialysis patients, overall MARD rises to 18.2 % (22.8 % during dialysis sessions) and only 49‑51 % of readings fall within acceptable error‑grid zones A/B【11】.
• Peritoneal dialysis patients should avoid FreeStyle Libre because icodextrin interferes with the glucose‑oxidase sensor【12】.

4.2 Technological Interference

• The glucose‑oxidase sensor is vulnerable to interference from substances commonly present in kidney disease【12】.

5. Medication and Substance Interference

• Salicylic acid and ascorbic acid can compromise sensor accuracy【12】.
• Acetaminophen does not interfere with FreeStyle Libre measurements, unlike some other CGM platforms【12】.

6. Comprehensive Data Evaluation

• After meeting the minimum data criteria (≥14 days, ≥70 % active time), clinicians should assess the full set of ten standardized CGM metrics, not solely mean glucose, to capture hypoglycemia risk and variability【10】.