High and low alarm thresholds are not the same as the boundaries of your target blood glucose levels. You don’t want to hear an alarm every time your blood glucose goes slightly out of target range (we call these “nuisance alarms”), but you do want to be notified of high or low blood glucose in time to correct the problem and prevent a crisis. When setting the threshold levels for your alarms, keep the lag effect in mind. When blood glucose levels are dropping, the CGM value is likely to be a bit higher than your actual blood glucose level. And when they are rising, the CGM number will probably be a bit lower. For this reason, it is a good idea to set the low alert threshold at 80 mg/dl or higher, and the high alert in the 200–250 mg/dl range. To avoid being woken up by nuisance alarms, many people choose to set their high threshold a bit higher and their low threshold a bit lower during the night.
Now get a good night’s sleep. If you use a CGM system, tomorrow you’ll have a lot of analyzing to do!