As a rule, basal insulin doses are assessed based on changes in the glucose level during the night. Here, it is necessary to separate temporary variation, periodic variation and more continuous, recurring, significant changes in the glucose level overnight. A change in excess of ± 2–3 mmol/l overnight is considered to be significant.
Use the glucose trend to evaluate the change in blood sugar from midnight to the time you wake up.
If the glucose trend is level during the night, in all likelihood, the basal insulin dose is correct.
If the night-time glucose trend is descending, the basal insulin effect and the dose were too large.
If the night-time glucose trend is ascending, the basal insulin effect and the dose were too small.
Temporary variation may be linked to physical exercise on the day before or an otherwise unusual daily rhythm. Periodic variation may be related to, e.g. different weekdays or daily routines, stress or, in the case of women, the menstrual cycle. An increase in the glucose level over a longer period of time or decline overnight is a sign that the dose of basal insulin is either too small or too big. For different basal insulin products, the time of injection may also matter.
If your blood glucose level drops too low in the early part of the night straight after you have gone to bed, it may also be because the bolus insulin dose you took for supper was too big.
At daytime, the correct basal insulin dose can be determined on the basis of your glucose level before dinner and supper. If the basal insulin dose and timing have been correct, but the pre-meal glucose level is too high and the glucose curve tends to rise between meals, the current basal insulin dose is likely too small. Conversely, if the glucose level drops low before meals and between them, the effect of the basal insulin might be too large. However, it is worth keeping in mind what you have done in the previous couple of hours. For instance, if it has not been long since your last snack or exercise, the pre-meal measurement may not reliably reflect the effect of the basal insulin. When evaluating doses, it's also good to record information about, for example, exercise, so you can assess the impact of various factors on the glucose level fluctuations.