Most real-time continuous glucose monitoring (rt-CGM) systems feature trend arrows. The graphical representation of these trend arrows differ with different manufacturers, but in general upward-pointing arrows show increasing glucose trends while downward-pointing arrows show decreasing glucose trends. Working with trend arrows is one of the essential skills required to get the best results from rt-CGM systems.
Upwards arrows are important for meal and correction insulin doses. In these situations, insulin should be administered according to the predicted sensor glucose readings at 30 minutes, and meal insulin should be administered 15 minutes before a meal. On the other hand, downward arrows are important for meal and correction insulin doses, as well as exercise and sleep. In these situations, meal insulin should be administered immediately before meal based on the predicted sensor glucose at 30 minutes. If the patient is not planning to eat, they are advised to monitor their sensor readings and may need to consume a small amount of carbohydrate (5 to 10 grams) to prevent hypoglycaemia. They are also advised not to start exercise or go to bed until the trend arrows are horizontal.
It is important to remember that over-correction for both upward and downward trend arrows tend to cause a yo-yo effect on sensor glucose readings, hence smaller corrective measures (either by insulin or carbohydrates) are often preferred.
The following tables summarize the predicted glucose changes and recommendations for different trend arrows with both Abbott Freestyle Libre and Medtronic Guardian systems.
