Comparison of Glucose Concentrations between Flash and Continuous Monitoring Systems in Patients with Diabetes Mellitus

Flash glucose (FGMS) and continuous glucose (CGMS) monitoring systems are becoming increasingly prevalent in clinical practice. We directly compared FGMS (FreeStyle Libre-Pro, FSL-Pro) and CGMS (iPro2) in a patient with diabetes mellitus (T1DM/T2DM = 3/10). Analysis of 7,365 paired values revealed a close correlation between FSL-Pro and iPro2 glucose values (r = 0.93, p < 0.01). Parkes error grid analysis showed that 93.3%, 6.2%, 0.5% and 0.04% of all glucose pairs fell within areas A, B, C and D, respectively, whereas no values was located in area E. Median glucose values were significantly lower for FSL-Pro than iPro2 (149.0 (115.0-187.0) vs. 171.0 (138.0-213.0) mg/dL, p < 0.01). Notably, 89.3% of all glucose values were lower for FSL-Pro than iPro2; therefore, the difference between them was considerable (Figure 1; r = -0.273, p < 0.01). The absolute difference between FSL-Pro and iPro2 glucose values was significantly higher among hyperglycemic values (>180 mg/dL) compared with normoglycemic values (70-180 mg/dL) (32.0 (19.0-47.0) vs. 23.0 (14.0-31.0) mg/dL, p < 0.05). We concluded that glucose values are lower when measured using FSL-Pro than iPro2 and this tendency became more pronounced under conditions of hyperglycemia.