How to use this guide. A desk reference for reading a CGM report in a non-diabetic or metabolic health context. Each metric is defined in the key below. References are numbered in square brackets and listed in full at the end.
Metric Definitions Key
All abbreviations spelled out
▶
SDBG
Standard Deviation of Blood Glucose
How much glucose varies above and below the average. Low SDBG = stable. High SDBG = large swings.
Fasting glucose
Overnight / morning baseline
Glucose level before eating. Reflects how well the body regulates blood sugar at rest overnight.
Post-Meal Peak
Post-meal glucose rise
How much glucose rises above the pre-meal level after eating. Peak reading minus pre-meal reading.
CV
Coefficient of Variation
Day-to-day stability score as a percentage. Lower is steadier.
TIR
Time in Range
Percentage of the day glucose stays within 3.9–7.8 mmol/L. Higher is better.
TAR
Time Above Range
Percentage of readings above 7.8 mmol/L. Flags how often glucose runs too high.
TBR
Time Below Range
Percentage of readings below 3.9 mmol/L. Flags how often glucose drops too low.
GMI
Glucose Management Indicator
Estimated average glucose health from sensor data — useful for tracking trends. Do not assume this equals the client's HbA1c; GMI and lab HbA1c can differ with certain blood conditions or unusual red cell turnover.
IFG
Impaired Fasting Glucose
Fasting glucose 6.1–6.9 mmol/L — above normal, not yet diabetic range. A GP referral signal, not a diagnosis.
1. Priority Read Order
The hierarchy that surfaces early dysfunction
▶
In non-diabetic clients, mean glucose is usually unremarkable. Variability and fasting regulation are where early dysfunction shows up first. Read in this order:
- SDBG (Standard Deviation of Blood Glucose) — the corridor width; wide swings signal poor glucose regulation.
- Fasting glucose — overnight profile and dawn rise; elevated fasting glucose shows before other markers.
- Post-Meal Peak — glucose rise above pre-meal baseline; exaggerated peaks indicate impaired early-phase insulin response.
- CV (Coefficient of Variation) — day-to-day stability score; comparable across clients with different mean glucose levels.
- Average (Average Sensor Glucose) — the last value to deteriorate; useful as a final check rather than a primary signal.
2. Non-Diabetic Reference Values
Shah 2019 — n = 153 healthy adults, 10-day Dexcom G6
▶
Source: Shah 2019 [1] — n = 153 healthy adults, 10-day Dexcom G6.
| Metric | Non-diabetic reference | Early-signal zone |
|---|---|---|
| SDBG | ~0.9 mmol/L | >1.2 mmol/L |
| Fasting glucose | 4.5–5.5 mmol/L | ≥ 6.1 mmol/L (see referral triggers) |
| Post-Meal Peak | 1.5–2.5 mmol/L above pre-meal; peak <7.8 | Rise >3.5 mmol/L or peak >8.5 mmol/L |
| CV | 17 ± 3% | >25% |
| Time in Range (TIR) 3.9–7.8 mmol/L | 96% (IQR 93–98) | <90% sustained over 14 days |
| Time Above Range (TAR) >7.8 mmol/L | 2.1% (~30 min/day) | >10% sustained |
| Time Below Range (TBR) <3.9 mmol/L | 1.1% (~15 min/day) | >3% sustained with symptoms |
| Average (sensor glucose) | 5.4–5.5 mmol/L (5.8 if >60 yrs) | Rising trend across consecutive months |
Note on data source. Shah's dataset (n = 153, Dexcom G6) provides the best available non-diabetic reference. Use 96%+ TIR 3.9–7.8 as the working benchmark — a sound clinical reference, not a regulatory standard.
3. Referral Triggers — GP Investigation
Screening signals, not diagnoses
▶
These are screening signals, not diagnoses.
| Signal | Threshold |
|---|---|
| Fasting glucose | ≥ 6.1 mmol/L (Impaired Fasting Glucose) or ≥ 7.0 mmol/L on two separate occasions (diabetic range) |
| Any single sustained reading | ≥ 11.1 mmol/L |
| 14-day average with symptoms | ≥ 6.5 mmol/L |
| Persistent hypoglycaemia | Time Below Range <3.9 mmol/L exceeding 3% with associated symptoms |
Scope of practice. CGM in non-diabetic coaching is a screening tool, not a diagnostic instrument. These thresholds warrant a GP conversation — they do not replace one.
4. Lactate — The Emerging Metric
The next monitoring frontier
▶
Good CGM numbers do not tell the whole story. A client can have Time in Range above 95% and stable CV — and still have a poor lactate profile. Lactate is the next monitoring frontier.
- Fasting lactate can rise before fasting glucose shows any sign of dysfunction [2].
- Mitochondrial dysfunction can be present in lean, insulin-resistant individuals with entirely normal fasting glucose, HbA1c and BMI [3].
About the Founder
Spencer Martin · Glucose Evolution
▶
Spencer Martin
Founder, Glucose Evolution · 15+ Years in Continuous Glucose Monitoring
Spencer Martin founded Glucose Evolution after 15 years in the CGM industry, having seen first-hand how real-time glucose data transforms outcomes in Type 1 diabetes — and asking why that same insight wasn't being used earlier, before metabolic dysfunction takes hold. Glucose Evolution exists to change that, responsibly and within appropriate scope of practice.
References
4 primary sources
▶
[1] Shah VN, DuBose SN, Li Z, et al. Continuous Glucose Monitoring Profiles in Healthy Nondiabetic Participants: A Multicenter Prospective Study. J Clin Endocrinol Metab 2019;104(10):4356–4364. DOI: 10.1210/jc.2018-02763. PMID: 31127824.
[2] Broskey NT, Pories WJ, DeMaria EJ, et al. Fasting Plasma Lactate as a Possible Early Clinical Marker for Metabolic Disease Risk. Diabetes Metab Syndr 2024;18(2):102955. PMID: 38382370.
[3] Petersen KF, Dufour S, Befroy D, Garcia R, Shulman GI. Impaired Mitochondrial Activity in the Insulin-Resistant Offspring of Patients with Type 2 Diabetes. N Engl J Med 2004;350(7):664–671. PMID: 14960743.
[4] Guzzi J, Falter F, Kumar AB, Perrino AC. Mind the Gap: Wearable Lactate and Glucose Monitors for Hospitalized Patients. Cureus 2025;17(2):e78536. DOI: 10.7759/cureus.78536.