Coefficient of variation (CV) for glucose is standard deviation divided by mean glucose, expressed as a percent. The international consensus target is CV less than or equal to 36 percent. CV captures glycemic variability that A1C and mean glucose miss — and high CV is a strong predictor of hypoglycemia risk.
How CV Is Calculated
- Collect all CGM glucose readings over a window (usually 14 days).
- Compute the mean glucose.
- Compute the standard deviation (SD) of the readings.
- CV (%) = (SD / mean) × 100.
- Most CGM software (Dexcom Clarity, FreeStyle LibreView, etc.) calculates CV automatically.
Worked Example
| 14-Day Mean Glucose (mg/dL) | SD (mg/dL) | CV (%) | Interpretation |
|---|---|---|---|
| 140 | 30 | 21.4 | Excellent — very stable |
| 150 | 45 | 30.0 | Good — within target |
| 160 | 58 | 36.3 | At threshold — hypoglycemia risk increasing |
| 170 | 72 | 42.4 | High variability — hypoglycemia risk significant |
| 180 | 90 | 50.0 | Very high — frequent hypoglycemia likely |
| 200 | 120 | 60.0 | Severe variability — review therapy urgently |
Why 36 Percent Is the Target
The Monnier et al. 2017 analysis of CGM data found that hypoglycemia (less than 70 mg/dL) frequency rose sharply above CV of about 36 percent. Below 36 percent, lows were rare even with moderate mean glucose. Above 36 percent, lows became common — and increased disproportionately with each percentage point higher. The Battelino 2019 international consensus adopted CV less than or equal to 36 percent as the variability target.
CV vs Other Variability Metrics
| Metric | What It Captures | Typical Target |
|---|---|---|
| SD (standard deviation) | Absolute spread in mg/dL | <50 mg/dL (rough guidance) |
| CV (coefficient of variation) | Spread normalized to mean | ≤36% |
| MAGE | Mean amplitude of large excursions | <60 mg/dL (rough guidance) |
| MODD | Mean of daily differences (day-to-day stability) | <40 mg/dL |
| iAUC | Incremental area under curve (post-meal exposure) | Lower is better |
CV is the most commonly reported in clinical CGM software because it is easy to calculate and normalize. For an explanation of MAGE and how it differs from CV, see our companion guide.
Why Variability Matters Independently
- Hypoglycemia risk: the dominant clinical reason. High CV means more frequent lows at the same average glucose.
- Oxidative stress: glucose swings generate more reactive oxygen species than steady hyperglycemia in lab and animal models.
- Endothelial dysfunction: rapid glucose changes injure the vascular lining.
- Inflammation: markers like IL-6 and TNF-alpha rise with variability.
- Patient-perceived burden: people with high CV report more fatigue, cognitive symptoms, and quality-of-life impact.
- Possible independent contribution to complications: evidence is mixed; some trials suggest variability adds risk beyond mean glucose, others do not.
What Drives High CV
- Insulin therapy with imprecise dosing or timing.
- Inconsistent meals — variable carb amounts and timing.
- Gastroparesis (variable absorption).
- Alcohol — delays liver glucose output, causes late lows.
- Exercise without dose adjustment.
- Stress and acute illness.
- Overcorrection — large insulin doses for hyperglycemia followed by overshoot and hypoglycemia.
- Dawn phenomenon and Somogyi effect — see our dawn phenomenon vs Somogyi guide.
- Hormonal variability (menstrual cycle, thyroid disorders).
- Pump malfunction or insulin spoilage.
Strategies to Lower CV
| Strategy | Typical CV Reduction |
|---|---|
| Automated insulin delivery (AID) | 5 to 10 percentage points |
| Accurate carb counting | 2 to 5 points |
| Pre-meal insulin timing (15 min before) | 2 to 4 points |
| Consistent meal timing and content | 3 to 6 points |
| Lower-carb / lower-GI diet | 3 to 5 points |
| Post-meal walking | 2 to 4 points |
| Stop overcorrecting highs | 2 to 5 points |
| Address gastroparesis | 3 to 8 points |
| Switch from NPH to glargine or degludec | 3 to 6 points |
The biggest single intervention for most people is reducing hypoglycemia. Eliminating lows compresses the distribution and lowers CV mechanically.
CV in Different Populations
- Type 1 diabetes: CV typically 30 to 45 percent on multiple daily injections; 25 to 35 percent on AID.
- Type 2 on insulin: CV typically 25 to 40 percent.
- Type 2 on oral agents: CV typically 18 to 28 percent.
- People without diabetes: CV typically less than 17 percent.
- Pregnancy: tighter targets — CV less than 30 percent ideal.
- Older adults: CV less critical than absolute hypoglycemia avoidance.
When to Pay Closer Attention to CV
- Recurrent unexplained hypoglycemia.
- Hypoglycemia unawareness.
- Frequent severe hypoglycemia requiring assistance.
- Wide swings reported by patient (“rollercoaster”).
- Considering CGM upgrade or AID system.
- Pregnancy planning or active pregnancy.
- Switching insulin regimens.
- Workup for brittle diabetes.
Limitations of CV
- Requires CGM data — not available from fingerstick alone.
- Sensor noise affects calculated SD (and therefore CV).
- Does not show the timing of variability (e.g., postprandial vs nocturnal).
- Mean glucose context still matters — CV of 40 percent with mean 130 is different from CV of 40 percent with mean 200.
- Tight CV achieved with very low mean glucose may hide significant hypoglycemia.
- Different 14-day windows can give noticeably different CV values during therapy changes.
How to Use CV in Practice
- Find CV on your AGP report or in the CGM app summary.
- Note whether CV is above or below 36 percent.
- If above 36 percent, look at TBR — eliminating lows is the highest-yield action.
- Identify daily patterns: morning highs followed by post-meal lows? Overnight swings?
- Adjust one thing at a time: meal carbs, insulin timing, basal rate, or activity timing.
- Recheck CV after 2 weeks of stable behavior.
- Combine CV with TIR and TBR for a complete picture.
Related Reading
See Time in Range, GMI vs A1C, MAGE and glucose variability, and Ambulatory Glucose Profile.
The Bottom Line
Coefficient of variation for glucose normalizes glycemic variability — standard deviation divided by mean, times 100. Target CV less than or equal to 36 percent. Above 36 percent, hypoglycemia becomes frequent and unpredictable, regardless of A1C. CV captures what averages miss: how much your glucose swings. Lower CV through consistent meals, accurate insulin timing, AID systems, and elimination of lows. Review CV alongside TIR, TBR, and GMI to get the complete picture of glycemic control.
