The FreeStyle Libre Flash glucose monitoring system is a continuous glucose monitoring system that is used worldwide for improving plasma glucose control in patients with diabetes mellitus. Although we have used six different lots of the sensors, we recently and unexpectedly noted that one of the sensors for the FreeStyle Libre system showed completely different measured values. Herein, we designated these six lots as lot A through F. We observed that 53.4% and 54.6% of repeatedly measured interstitial glucose levels by Lot A were below 80 mg/dL (We tested two of Lot A on different day to confirm reproducibility.). On the other hand, the rest of 5 Lots (Lot B through F) showed that 0% of repeatedly measured interstitial glucose levels was below 80 mg/dL. However, unexpectedly, SMBG using a FS precision electrode with using the same reader of FreeStyle Libre system measured completely different values. Thus, Lot A consistently showed lower measured values compared to with those obtained using SMBG. As measured values using the FreeStyle Libre system are considered to be accurate as well as those obtained by SMBG, we decided to simultaneously test different lots of sensors, although the arm-attached sensor for B was on a different side than that for lot A. Lot A consistently showed measured values that were 20-30 mg/dL lower than those of Lot B. It is obvious that one of the six different lots showed inappropriately lower measured values and these discrepancies were critical. Therefore, it is possible that some lots of sensors for the FreeStyle Libre system do not work correctly, and may lead to false readings of hypoglycemia and a delayed response to true hyperglycemia, which requires a rapid response.
In summary, when changing of the lots of sensors for the FreeStyle Libre glucose monitoring system, we recommended that patients double check measured values using an alternative method, such as SMBG, as soon as possible to avoid incorrect blood glucose control.
J. Okada: None. S. Okada: None. M. Yamada: None.
