Confusion Regarding Duration of Insulin Action: A Potential Source for Major Insulin Dose Errors by Bolus Calculators

People with diabetes on insulin pumps often use a bolus calculator (BC) to obtain insulin dose recommendations. After the first bolus of the day, residual insulin activity, called bolus insulin on board (BOB), must be correctly accounted for to reduce the size of subsequent boluses and minimize the insulin stacking that would otherwise occur. Critical to achieving this calculation is having an appropriate duration of insulin action (DIA) setting in the BC. Unfortunately, the widespread use of inappropriately short DIAs may be causing unrecognized "stacking" of insulin that leads to unexplained hypoglycemic events. Currently, there is no widely accepted definition or value of the DIA for use in a BC. Various shortcomings regarding the selection of an appropriate DIA setting have led to considerable confusion among clinicians and insulin pump users about this important concept. Traditional pharmacological studies used to determine the pharmacodynamic (PD) properties of rapid-acting insulins create a misleading impression that insulin action times (IATs) in daily life vary from 3 to 5 hours and cause IATs to appear more variable than they actually are. These IAT time ranges are not appropriate for use as the DIA time value required to obtain an accurate bolus recommendation from a BC. We highlight the problems that arise when an inappropriately short DIA leads to excessive bolus recommendations, provide a research protocol to accurately measure DIA, and suggest appropriate DIA time recommendations for use in current clinical practice.