CGM trend arrows are as important as the glucose number itself. They tell you not just where your glucose is, but where it is going — and how fast. Misreading an arrow can lead to under- or over-treatment.
The Five Trend Arrows
- ↑↑ Double Up: Rising faster than 3 mg/dL/min (>2 mmol/L/min). Glucose rising very fast — act soon if above target
- ↑ Single Up: Rising 2-3 mg/dL/min. Significant rise in progress
- ↗ Diagonal Up: Rising 1-2 mg/dL/min. Moderate rise — monitor closely
- → Horizontal (Flat): Stable, changing less than 1 mg/dL/min. Glucose is steady
- ↘ Diagonal Down: Falling 1-2 mg/dL/min. Moderate fall — have carbs available
- ↓ Single Down: Falling 2-3 mg/dL/min. Significant drop — treat soon if symptomatic
- ↓↓ Double Down: Falling faster than 3 mg/dL/min. Fast drop — treat immediately, verify with fingerstick
Why the Arrow Matters as Much as the Number
A glucose reading of 110 mg/dL with a double down arrow (↓↓) is very different from 110 mg/dL with a flat arrow (→). In the first case, you may be heading toward hypoglycemia within minutes. In the second, you are stable.
Practical Rules of Thumb
- Single up (↑): for every 1 mg/dL/min of rise, expect glucose to be 20-30 mg/dL higher in 20 minutes if you take no action
- Single down (↓): consume 15g of fast carbs if you are below 80 mg/dL; more if double down
- Always verify with a fingerstick before treating severe hypoglycemia — CGM lag can underestimate a rapid drop
Lag Time and Arrow Interpretation
Remember that CGM reads interstitial fluid, which lags blood glucose by 5-15 minutes. When glucose is changing rapidly, the CGM number and arrow reflect where you were, not exactly where you are now. Add the lag when interpreting arrows during meals or after insulin.
Eating and Post-Meal Arrows
Expect a ↑ or ↑↑ arrow for 1-2 hours after a high-carb meal. This is normal. The target is to be back to horizontal (→) within 2 hours of eating. If you regularly see ↑↑ arrows persisting for 3+ hours, discuss with your diabetes care team.