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Numerical and Clinical Accuracy of the FreeStyle Libre 2 System: A Diagnostic Accuracy Study in Critically Ill
Miguel Aguilar-Schotborgh1, Oscar Muñoz-Velandia1,2, Diana Cristina Henao-Carrillo1,3
1Department of Internal Medicine, Pontificia Universidad Javeriana, Bogotá, Colombia.
Background:
The accuracy of the FreeStyle Libre 2 system in critically ill patients needing insulin therapy remains inadequately evaluated.
Objective:
To evaluate the clinical and numerical accuracy of continuous glucose monitoring (FreeStyle Libre 2) and capillary glucometry (StatStrip) compared with central laboratory glucose in critically ill patients requiring insulin therapy.
Methods:
We conducted a diagnostic accuracy study, evaluating simultaneously two index tests, the FreeStyle Libre 2 and capillary glucose, compared to the central laboratory glucose (venous or arterial) as reference standard. The study included critically ill adult patients admitted to the intensive care unit (ICU) with diabetes or stress hyperglycemia, requiring insulin therapy, and ventilatory or vasopressor support. Numerical accuracy was assessed using ISO 15197:2013 criteria and Mean Absolute Relative Difference (MARD). Clinical accuracy was evaluated using Clarke and Parkes error grid analysis.
Results:
A total of 157 paired measurements were collected. FreeStyle Libre 2 showed a MARD comparable to capillary glucose (10.43% vs 7.58%; p=0.14). Neither method met ISO 15197:2013 numerical accuracy criteria. In the clinical accuracy analysis, FreeStyle Libre 2 classified 100% of measurements within zones A+B on both the Clarke and Parkes grids, whereas capillary glucose achieved 97.6% and 100%, respectively.
Conclusions:
FreeStyle Libre 2 showed numerical accuracy comparable to capillary blood glucose and consistently reliable clinical performance in critically ill patients needing insulin therapy. These results support its potential as an alternative to capillary glucose monitoring in the ICU. More studies involving a greater number of hypoglycaemic events are required to confirm its effectiveness in this critical range.