The accuracy of the Guardian RT continuous glucose monitor in children with type 1 diabetes

Abstract

Objective: The aim of this study was to determine the accuracy of the Guardian RT system (Medtronic Minimed, Northridge, CA) in young children and adolescents with type 1 diabetes (T1D) during different scenarios of glucose levels and sensor age.

Methods: At five clinical centers, 30 subjects between 4 and 17 years old with T1D were recruited. All subjects had a glycosylated hemoglobin level of <or=10.0% and were using an insulin pump. Subjects initially used a Guardian RT for approximately 1 week at home. Each subject was then hospitalized overnight for about 18 h in a clinical research center, during which time insulin-induced hypoglycemia occurred, along with frequently sampled glucose.

Results: There were 1,511 laboratory glucose measurements paired with glucose measurements from 48 Guardian RT sensors. Overall, the median absolute difference (AD) was 21 mg/dL, and the median relative AD (RAD) was 14%, with 64% of sensor values meeting International Organization for Standardization home glucose meter criteria. The median AD was 27 mg/dL for reference glucose values<or=60 mg/dL and 25 mg/dL for reference glucose values<or=70 mg/dL. The median RAD was 19% for reference glucose values 71-120 mg/dL, 14% for reference glucose values 121-180 mg/dL, and 10% for reference glucose values>180 mg/dL.

Conclusions: The Guardian RT appears to perform as well in children with T1D as it has been reported to perform in adults with diabetes. The Guardian RT has an accuracy similar to that of other available continuous glucose monitors and can give important and useful clinical information.

FIG. 1.

Guardian RT versus laboratory-measured drops in glucose during insulin testing (n = 47 sensors from 28 subjects). Drop in glucose was defined from baseline to nadir. The sensor nadir glucose was defined as the extrapolated nadir in 20 min following treatment based on the 15-min rate of change of the sensor right before treatment. Note one sensor read 40 mg/dL (the minimal value of the sensor) during the entire test, so the sensor defined drop was zero.

FIG. 2.

Guardian RT versus laboratory rate of change during insulin testing (n = 47 sensors from 28 subjects). Rate of change for the laboratory reference was defined from the blood sample at the Ultra meter glucose <90 mg/dL to the first time laboratory reference values dropped below 70 mg/dL (approximately 90 mg/dL to <70 mg/dL) and was compared to the rate of change of Guardian RT in the same period.

FIG. 3.

Guardian RT versus laboratory-measured rises in glucose following dinner (n = 32 sensors from 19 subjects).

FIG. 4.

Guardian RT versus laboratory-measured rises in rates of change following dinner (n = 32 sensors from 19 subjects).