Continuous glucose monitoring system: Is it really accurate, safe and clinically useful?

Abstract

The continuous glucose monitoring system (CGM) has been used for constant checking of glucose level by measuring interstitial glucose concentrations, since the early days of the 21st century. It can potentially improve diabetes care if used carefully with the understanding of the characteristics of this system. Although there is a time lag of approximately 5-15 min between blood and interstitial glucose levels, the system is considered the most suitable device for meticulous glucose control and prevention of hypoglycemia. A large number of studies have examined its accuracy, safety and clinical effectiveness. The continuous glucose-error grid analysis (CG-EGA), designed by WL Clarke, evaluates the clinical accuracy of CGM. It examines 'temporal' characteristics of the data, analyzing pairs of reference and sensor readings as a process in time represented by a 'bidimensional' time series and taking into account inherent physiological time lags. Investment in CG-EGA is clearly meaningful, even though there are other methodologies for evaluation. The use of each method complementarily is the most effective way to prove the accuracy of the device. The device has improved gradually, and real-time CGM, which allows real-time monitoring of blood glucose level, is already available commercially. The use of real-time CGM could potentially lead to over- or undertreatment with insulin. Patient education through proper and effective handling of the new device is essential to improve diabetes care. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00197.x, 2012).

Keywords: Continuous glucose monitoring system; Continuous glucose‐error grid analysis; Patient education.

Figure 1

The rate‐error grid analysis (R‐EGA) divided into AR, BR, CR, DR and ER for sensor blood glucose (SBG) rate vs reference blood glucose (RBG) rate. The R‐EGA zones extend theoretically to infinity. l, Lower; R, rate; u, upper.

Figure 2

The point‐error grid analysis (P‐EGA) divided into AP, BP, CP, DP and EP for sensor blood glucose (SBG) vs reference blood glucose (RBG). The P‐EGA zones are defined based on the reference rate of changes in blood glucose. l, Lower; p, point; u, upper.

Figure 3

The continuous glucose‐error grid analysis (CG‐EGA) computes the accuracy of the combination of rate‐error grid analysis (R‐EGA) plus point‐error grid analysis (P‐EGA) into three clinically relevant regions: hypoglycemia (blood glucose ≤70 mg/dL), euglycemia and hyperglycemia (blood glucose >180 mg/dL). BG, blood glucose; l, lower; u, upper.