The study is to demonstrate the accuracy of the OptiScanner in measuring blood glucose levels in critically ill patients when compared to a reference YSI 2300 STAT Plus and the Gem 3000, the reference standard for Erasme University Hospital.

Inclusion Criteria:

• Signed Informed consent.
• Age ≥ 18 years.
• Admitted to the ICU of Erasme University Hospital.
• Expected ICU stay of ≥ 3 days at the time of enrollment (as judged by the Principle Investigator).
• APACHE II score of ≥ 10, within the first 24 hours of ICU admission.
• Existing central venous catheter + arterial catheter.
• No participation in any other investigational interventional study while enrolled in this study.
• Hyperglycemia (BG > 150 mg/dl) at the time of admission.

Exclusion Criteria:

• Pregnancy.

Critically ill patients admitted to the intensive care unit (ICU) of Erasme University Hospital in Brussels, Belgium.