['Hyperglycemia and glycemic variabilities are associated with adverse outcomes in critically ill patients. Blood glucose control with insulin mandates an adequate and precise assessment of blood glucose levels. Blood glucose levels, however, can change ex vivo after sampling. The aim of this study was to determine whether this phenomenon affects the practice of blood glucose control.', 'We performed an observational study in a mixed medical-surgical intensive care unit (ICU). ICU nurses were the primary healthcare workers involved in the practice of blood glucose control, and they used an insulin-titration method and blood-sampling algorithm aimed at maintaining blood glucose levels between 5 to 8 mmol/L.', 'Blood glucose levels were measured directly after sampling, as well as after 30 and 60 minutes using the same samples. Blood glucose control algorithm recommendations were scored for each measurement. We collected 450 blood samples from 74 patients (median of 3 [2-8] samples per patient). The mean ex vivo changes in the blood glucose level were rather small (-0.1±1.6 mmol/L (range -1.4 to 0.7) and -0.2±1.6 mmol/L (range -1.3 to 0.5) at 30 and 60 minutes after sampling, respectively; P<0.05). An ex-vivo change in the blood glucose level hardly ever resulted in a change in algorithm recommendation (4% and 6% at 30 and 60 minutes after sampling, respectively). In most cases the algorithm advised a lower insulin infusion speed.'] Do ex vivo changes in blood glucose levels seldom change blood glucose control algorithm recommendations?