Median Absolute Relative Difference Research Articles

Use of the Site of Subcutaneous Insulin Administration for the Measurement of Glucose in Patients With Type 1 Diabetes

OBJECTIVETo simplify and improve the treatment of patients with type 1 diabetes, we ascertained whether the site of subcutaneous insulin infusion can be used for the measurement of glucose.RESEARCH DESIGN AND METHODSThree special indwelling catheters (24-gauge microperfusion [MP] catheters) were inserted into the subcutaneous adipose tissue of subjects with type 1 diabetes (n = 10; all C-peptide negative). One MP catheter was perfused with short-acting insulin (100 units/ml, Aspart) and used for insulin delivery and simultaneous glucose sampling during an overnight fast and after ingestion of a standard glucose load (75 g). As controls, the further two MP catheters were perfused with an insulin-free solution (5% mannitol) and used for glucose sampling only. Plasma glucose was measured frequently at the bedside.RESULTSInsulin delivery with the MP catheter was adequate to achieve and maintain normoglycemia during fasting and after glucose ingestion. Tissue glucose concentrations derived with the insulin-perfused catheter agreed well with plasma glucose levels. Median correlation coefficient and median absolute relative difference values were found to be 0.93 (interquartile range 0.91–0.97) and 10.9%, respectively. Error grid analysis indicated that the percentage number of tissue values falling in the clinically acceptable range is 99.6%. Comparable analysis results were obtained for the two mannitol-perfused catheters.CONCLUSIONSOur data suggest that estimation of plasma glucose concentrations from the glucose levels directly observed at the site of subcutaneous insulin infusion is feasible and its quality is comparable to that of estimating plasma glucose concentrations from glucose levels measured in insulin-unexposed subcutaneous tissue.

New Features and Performance of a Next-Generation SEVEN-Day Continuous Glucose Monitoring System with Short Lag Time

The purpose of this study was to evaluate new features and performance of the SEVEN PLUS System (DexCom, Inc., San Diego, CA), a real-time continuous glucose monitoring (CGM) device. This study is the first to evaluate the SEVEN PLUS device. Fifty-three subjects were enrolled at three U.S. centers; 43 (81%) of the subjects had type 1 diabetes mellitus, and 10 (19%) had insulin-requiring type 2 diabetes mellitus. Subjects inserted and wore either one or two sensors for 7 days. A subgroup (n = 18) wore two sensors to track precision. Subjects participated in one 8-h in-clinic session with blood draws every 15 min on study Day 1, 4, or 7 to collect laboratory reference YSI instrument (YSI, Yellow Springs, OH) and self-measured plasma glucose (SMPG) reference measurements. For the remainder of the week, CGM was used as an adjunct to SMPG during home use. The overall median absolute relative difference (ARD) versus YSI was 13.0%. Zones A and B of the Clarke Error Grid of CGM measurements were 73.8% and 22.1%, respectively. Precision ARD was 15.3 +/- 6.2% (mean +/- SD). The median ARD versus SMPG was 12.1%. Sensor life (89% lasted 7 days) was improved compared to the SEVEN device. The lag time obtained with various statistical measures between CGM and YSI were similar and estimated as a median of 8 min (interquartile range, 11 min) using the Pearson correlation coefficient. No serious adverse events or infectious complications were reported. The performance of this new system compares favorably to the previous SEVEN device in terms of accuracy, precision, lag time, sensor life, and rate of data capture.

Validation of SeaWiFS and MODIS aerosol products with globally distributed AERONET data

The validation of aerosol products derived from ocean color missions is required for the assessment of their uncertainties and as a diagnostic for the atmospheric correction schemes used for determining the ocean apparent optical properties. A comprehensive validation of the aerosol products obtained from the ocean color missions SeaWiFS and MODIS is presented; it relies on the field observations collected at 85 AERONET sites and is completed by preliminary results obtained with the data of the maritime AERONET component. A robust match-up selection protocol yields approximately 7000 match-ups for each sensor. The median absolute relative difference for the aerosol optical thickness τa increases from 20–22% at 443 nm to 45–48% in the near-infrared. The validation statistics are comparable for both sensors but MODIS results appear degraded particularly for sites located on isolated islands. The median absolute difference is approximately 0.03 at all wavelengths. Results are further analyzed for specific geographic regions or groups of sites selected to represent oceanic, continental, or desert dust conditions. Importantly, the match-up sets appear generally representative of the regional natural variability in τa amplitude and spectral shape, with the notable exception of high τa conditions that are excluded. An important finding is the underestimate by the atmospheric correction of the Ångström exponent α, with a median bias of − 0.52. This underestimate is apparent even at low α values and regularly increases with α. This discrepancy in τa spectral shape might result from an inappropriate set of candidate aerosol models and/or uncertainties in the calibration at the near-infrared bands. As the validation data base is expanded and updated in relation to new versions of the processing chains, this work provides a benchmark for the assessment of the aerosol products derived from the SeaWiFS and MODIS ocean color missions.

Use of Short-Term Real-Time Continuous Glucose Monitoring in Type 1 Diabetes Patients on Continuous Intraperitoneal Insulin Infusion: A Feasibility Study

In diabetes, strict glycemic control reduces risk of complications. One mode of therapy is continuous intraperitoneal insulin infusion (CIPII). With CIPII, like all intensified treatment strategies, frequent assessment of glucose levels is mandatory. Real-time (RT)-continuous glucose monitoring (CGM) gives RT information without the need for multiple invasive measurements. In theory, CIPII combined with RT-CGM could provide near normal glucose profiles. The objective of this study is to investigate effectiveness and safety of RT-CGM in patients treated with intraperitoneal insulin through an implanted pump. In an open-label, crossover, randomized study, effects of 6-day open RT-CGM use were studied in 12 type 1 diabetes patients on CIPII, with blinded RT-CGM used as a control. Primary outcome was time in euglycemia. Secondary outcomes included time in other glucose ranges, incidence of adverse events, and patient satisfaction. Agreement of self-measurement of blood glucose (SMBG) and RT-CGM measurements was assessed. Median time spent in euglycemia was 68.2% (55.9-72.3%) with open RT-CGM and 64.9% (55.3-71.2%) with blinded RT-CGM (P = 0.25). Time spent in other glucose ranges did not differ (P > 0.05). There were no serious adverse events. Patient satisfaction was good. Median relative absolute difference of SMBG and RT-CGM values was 13.9%. Bland-Altman analysis showed a mean difference of -0.31 mg/dL with lower and upper limits of agreement of -77.0 and +76.4 mg/dL, respectively. Short-term use of RT-CGM, although safe and with good patient satisfaction, does not result in more time spent in euglycemia, nor does it change time spent in other glucose ranges in our population of type 1 diabetes patients receiving CIPII.

Requirements for Calibration in Noninvasive Glucose Monitoring by Raman Spectroscopy

In the development of noninvasive glucose monitoring technology, it is highly desirable to derive a calibration that relies on neither person-dependent calibration information nor supplementary calibration points furnished by an existing invasive measurement technique (universal calibration). By appropriate experimental design and associated analytical methods, we establish the sufficiency of multiple factors required to permit such a calibration. Factors considered are the discrimination of the measurement technique, stabilization of the experimental apparatus, physics-physiology-based measurement techniques for normalization, the sufficiency of the size of the data set, and appropriate exit criteria to establish the predictive value of the algorithm. For noninvasive glucose measurements, using Raman spectroscopy, the sufficiency of the scale of data was demonstrated by adding new data into an existing calibration algorithm and requiring that (a) the prediction error should be preserved or improved without significant re-optimization, (b) the complexity of the model for optimum estimation not rise with the addition of subjects, and (c) the estimation for persons whose data were removed entirely from the training set should be no worse than the estimates on the remainder of the population. Using these criteria, we established guidelines empirically for the number of subjects (30) and skin sites (387) for a preliminary universal calibration. We obtained a median absolute relative difference for our entire data set of 30 mg/dl, with 92% of the data in the Clarke A and B ranges. Because Raman spectroscopy has high discrimination for glucose, a data set of practical dimensions appears to be sufficient for universal calibration. Improvements based on reducing the variance of blood perfusion are expected to reduce the prediction errors substantially, and the inclusion of supplementary calibration points for the wearable device under development will be permissible and beneficial.

Clinical Evaluation of a Transcutaneous Interrogated Fluorescence Lifetime-Based Microsensor for Continuous Glucose Reading

Continuous glucose monitoring is presently used worldwide. Accuracy, precision, durability, invasiveness, and lack of drift of sensors and lag time are key parameters essential to these systems. This article describes a new online minimally invasive biodegradable microsensor for optical, transcutaneous interrogation, which has at least 14 days of functionality. Studies were performed in vitro and in vivo on pigs, as well as on type 1 diabetic humans. Functionality has been ensured in laboratory settings, and precision and durability have been tested in vivo. During in vivo studies, venous blood samples were used as reference. Results were based on one single point calibration per experiment. Excellent stability was found in 14-day in vitro trials as well as in vivo in up to 70-hour trials. The overall median relative absolute difference of type 1 diabetic patients was 11.4%. Error grid analysis showed 97.7% of all values in the A+B zone. Comparable results were found in animal studies. No sensor drift was observed in any trial. Results point toward the possibility of developing a stable and precise minimally invasive glucose reader for at least 2 weeks of continuous use.

Feasibility of 10-Day Use of a Continuous Glucose-Monitoring System in Adults With Type 1 Diabetes

OBJECTIVE—The purpose of this pilot study was to evaluate the feasibility of 10-day use of a transcutaneous, real-time, continuous glucose-monitoring (CGM) system. All previous reports using different CGM systems were for 3-, 5-, or 7-day use.RESEARCH DESIGN AND METHODS—On day 1, subjects received the CGM device (SEVEN System) and underwent training on proper use. Subjects returned to the clinic on days 2, 7, and 10 for in-clinic sessions. On days 2 and 7, half the subjects performed fingersticks every 15 min and the other half had Yellow Springs Instruments (YSI) samples drawn every 15 min. On day 10, all subjects participated in an 8-h in-clinic session with YSI and fingerstick testing.RESULTS—The median absolute relative difference for CGM versus YSI was 12.6, 11.3, and 14.5% on days 2, 7, and 10, respectively (P = 0.63). CGM performed better on day 10 when compared with self-monitoring of blood glucose as compared with YSI.CONCLUSIONS—This is the first study to document 10-day use of a 7-day CGM system.

The Accuracy and Efficacy of Real-Time Continuous Glucose Monitoring Sensor in Patients with Type 1 Diabetes

The accuracy and efficacy of the Medtronic Diabetes (Northridge, CA) Real-Time (RT)-Continuous Glucose Monitoring (CGM) sensor were analyzed in 72 subjects with type 1 diabetes. This was a retrospective analysis of 60,050 temporally paired data points (sensor and glucose meter values) obtained during the course of an outpatient ambulatory study evaluating the efficacy of a sensor-augmented pump system in adults and adolescents. Subjects uploaded sensor values and self-monitoring blood glucose data to the CareLink Clinical Application (Medtronic Diabetes) via the Internet, every 2 weeks during the course of the study. The overall percentage of sensor readings within +/-20% or +/-30% agreement of reference glucose readings was 75.6% and 86.8%, respectively. The highest rate of agreement occurred in the 240-400 mg/dL range, where 79.9% of sensor readings were within +/-20% of meter values and 91.5% of sensor readings were within 30% of meter values. The mean absolute relative difference for all subjects was 15.8%, and the median absolute relative difference was 10.9%. The bias was -2.13 mg/dL. Paired glucose measurements from the RT-CGM and meter demonstrated that 95.9% of paired points in the overall subject population fell in zones A and B of the Clarke Error Grid. Consensus Error Grid Analysis established that 99.2% of paired data points were in zones A and B. This study reports the accuracy of a continuous glucose sensor with a large number of paired data points (60,050). RT-CGM is safe and well tolerated and provides readings that are in close agreement with glucose meter values.

The Accuracy of the Guardian®RT Continuous Glucose Monitor in Children with Type 1 Diabetes

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. 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. 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. 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.

Numerical simulation of the effect of rate of change of glucose on measurement error of continuous glucose monitors.

A 5-day in-patient study designed to assess the accuracy of the FreeStyle Navigator Continuous Glucose Monitoring System revealed that the level of accuracy of the continuous sensor measurements was dependent on the rate of glucose change. When the absolute rate of change was less than 1 mg*dl(-1)*min(-1) (75% of the time), the median absolute relative difference (ARD) was 8.5%, with 85% of all points falling within the A zone of the Clarke error grid. When the absolute rate of change was greater than 2 mg*dl(-1)*min(-1) (8% of the time), the median ARD was 17.5%, with 59% of all points falling within the Clarke A zone. Numerical simulations were performed to investigate effects of the rate of change of glucose on sensor measurement error. This approach enabled physiologically relevant distributions of glucose values to be reordered to explore the effect of different glucose rate-of-change distributions on apparent sensor accuracy. The physiological lag between blood and interstitial fluid glucose levels is sufficient to account for the observed difference in sensor accuracy between periods of stable glucose and periods of rapidly changing glucose. The role of physiological lag on the apparent decrease in sensor accuracy at high glucose rates of change has implications for clinical study design, regulatory review of continuous glucose sensors, and development of performance standards for this new technology. This work demonstrates the difficulty in comparing accuracy measures between different clinical studies and highlights the need for studies to include both relevant glucose distributions and relevant glucose rate-of-change distributions.

Relative Accuracy of The BD Logic®And FreeStyle®Blood Glucose Meters

The BD Logic((R)) (Becton, Dickinson and Co., Franklin Lakes, NJ) and FreeStyle((R)) (Abbott Diabetes Care, Alameda, CA) meters are used to transmit data directly to insulin pumps for calculation of insulin doses and to calibrate continuous glucose sensors as well as to monitor blood glucose levels. The accuracy of the two meters was evaluated in two inpatient studies conducted by the Diabetes Research in Children Network (DirecNet). In both studies, meter glucose measurements made with either venous or capillary blood were compared with reference glucose measurements made by the DirecNet Central Laboratory at the University of Minnesota using a hexokinase enzymatic method. The BD Logic tended to read lower than the laboratory reference regardless of whether venous (median difference = -9 mg/dL) or capillary blood (median difference = -7 mg/dL) was used. This resulted in lower accuracy of the BD Logic compared with the FreeStyle meter based on the median relative absolute difference (RAD) for both venous blood (median RAD, 9% vs. 5%, P < 0.001) and capillary blood (median RAD, 11% vs. 6%, P = 0.008). The greatest discrepancy in the performance of the two meters was at higher reference glucose values. Accuracy was not significantly different when the reference was < or = 70 mg/dL. The BD Logic meter is less accurate than the FreeStyle meter.

Accuracy of the 5-Day FreeStyle Navigator Continuous Glucose Monitoring System

The purpose of this study was to compare the accuracy of measurements of glucose in interstitial fluid made with the FreeStyle Navigator Continuous Glucose Monitoring System with Yellow Springs Instrument laboratory reference measurements of venous blood glucose. Fifty-eight subjects with type 1 diabetes, aged 18-64 years, were enrolled in a multicenter, prospective, single-arm study. Each subject wore two sensors simultaneously, which were calibrated with capillary fingerstick measurements at 10, 12, 24, and 72 h after insertion. Measurements from the FreeStyle Navigator system were collected at 1-min intervals and compared with venous measurements taken once every 15 min for 50 h over the 5-day period of sensor wear in an in-patient clinical research center. Periods of high rates of change of glucose were induced by insulin and glucose challenges. Comparison of the FreeStyle Navigator measurements with the laboratory reference method (n = 20,362) gave mean and median absolute relative differences (ARDs) of 12.8 and 9.3%, respectively. The percentage in the clinically accurate Clarke error grid A zone was 81.7% and that in the in the benign error B zone was 16.7%. During low rates of change (< +/-1 mg x dl(-1) x min(-1)), the percentage in the A zone was higher (84.9%) and the mean and median ARDs were lower (11.7 and 8.5%, respectively). Measurements with the FreeStyle Navigator system were found to be consistent and accurate compared with venous measurements made using a laboratory reference method over 5 days of sensor wear (82.5% in the A zone on day 1 and 80.9% on day 5).

Noninvasive Continuous Glucose Monitoring Using Photoacoustic Technology—Results from the First 62 Subjects

Continuous glucose monitoring is a useful tool for the achievement of improved glucose control in patients with diabetes. We tested the ability of a novel noninvasive continuous glucose monitor to track glucose excursions. The novel noninvasive Aprise sensor (Glucon Inc., Boulder, CO) utilizes the photoacoustic properties of the blood to infer the prevailing glucose levels. The performance of this sensor was tested in 62 subjects with diabetes who underwent an oral glucose tolerance, mixed meal, or glucose infusion test. The analysis included 979 pairs of reference values and sensor-derived glucose determinations. The mean of the relative absolute difference (RAD) of the sample was 19.9% with a median RAD of 13.2%. When results were plotted using the Clarke error grid, 66.5%, 28.1%, 1%, 4.4%, and 0% were within the A, B, C, D, and E ranges, respectively. The mean RAD for the oral glucose tolerance tests and meal tolerance tests was superior to the mean RAD of the glucose infusion studies (17% vs. 19% vs. 22%, respectively). Continuous noninvasive glucose monitoring using the Aprise sensor provides promising results. Such device may increase patient compliance and improve diabetes management.

The Accuracy of the FreeStyle Navigator Continuous Glucose Monitoring System in Children With Type 1 Diabetes

To evaluate the accuracy and precision of the FreeStyle Navigator continuous glucose monitoring system in children with type 1 diabetes. In 30 children with type 1 diabetes (mean age 11.2 +/- 4.1 years), the Navigator glucose values were compared with reference serum glucose values of blood samples obtained in an inpatient clinical research center and measured in a central laboratory using a hexokinase enzymatic method and in an outpatient setting with a FreeStyle meter. Median absolute difference (AD) and median relative absolute difference (RAD) were computed for sensor-reference and sensor-sensor pairs. The median AD and RAD were 17 mg/dl and 12%, respectively, for 1,811 inpatient sensor-reference pairs and 20 mg/dl and 14%, respectively, for 8,639 outpatient pairs. The median RAD between two simultaneous Navigator measurements (n = 1,971) was 13%. Ninety-one percent of sensors in the inpatient setting and 81% of sensors in the outpatient setting had a median RAD < or = 20%. The Navigator's accuracy does not yet approach the accuracy of current-generation home glucose meters, but it is sufficient to believe that the device has the potential to be an important adjunct to treatment of youth with type 1 diabetes.

Relationship of Fasting and Hourly Blood Glucose Levels to HbA1c Values

In this study, we evaluated the safety and efficacy of 7-day transcutaneous, real-time, continuous glucose monitoring (CGM) in subjects with insulin-requiring diabetes. Eighty-six subjects were enrolled at five U.S. centers. Subjects wore a sensor inserted under the skin of the abdomen for 7 days during each of three consecutive periods. Data were blinded during period 1 and unblinded during periods 2 and 3. Of the 6,811 matched self-monitoring of blood glucose to sensor values prospectively analyzed, 97.2% fell in the Clarke error grid zones A and B, and median absolute relative difference was 11.4%. After unblinding, subjects reduced time spent at <55 mg/dl by 0.3 h/day, reduced time spent at >240 mg/dl by 1.5 h/day, and increased time in the target zone (81-140 mg/dl) by 1.4 h/day (P < 0.05 for all three comparisons). Improvements were seen in both types 1 and 2 diabetes and with use of both multiple daily injections and continuous subcutaneous insulin infusion. Modal day graphs were generated in six groups of subjects based on HbA1c (A1C) (<or=6, 6-7, 7-8, 8-9, 9-10, and >10%). Mean glucose levels from midnight to 7:00 a.m. (fasting and dawn phenomenon periods) were only normal for subjects with A1C <or=6%. All other groups were hyperglycemic during this and all periods. Reductions in overall mean glucose were achieved for the four highest A1C groupings with unblinded device use. This is the first report of a real-time, transcutaneous glucose sensor that functioned for 7 days. The use of CGM in the unblinded phase resulted in improvements in target-range glycemia across all A1C values.

Improvement in Glycemic Excursions With a Transcutaneous, Real-Time Continuous Glucose Sensor

Hypoglycemia and wide glucose excursions continue to be major obstacles to achieving target HbA(1c) values and the associated reductions in long-term complications (and economic costs) in people with insulin-treated diabetes. In this study we evaluated the accuracy, safety, and clinical effectiveness of a continuous glucose-sensing device. A total of 91 insulin-requiring patients with type 1 (n = 75) and type 2 (n = 16) diabetes were enrolled in this multicenter randomized study. Subjects wore a transcutaneous, 3-day, continuous glucose-sensing system for three consecutive 72-h periods. Subjects were randomly assigned (1:1 ratio) to either a control group (continuous glucose data not provided) or a display group (continuous glucose data not provided during period 1 but displayed during periods 2 and 3). During periods 2 and 3, patients in the display group had real-time access to sensor glucose values, could review glucose trends over the preceding 1, 3, and 9 h, and were provided with high (> or = 200 mg/dl) and low (< or = 80 mg/dl) alerts and a low (< or = 55 mg/dl) alarm. Sensors were inserted by patients, and both groups used (or wore) the system during daily activities. Device accuracy was assessed by comparing continuous glucose values to paired self-monitoring of blood glucose (SMBG) meter readings. Clinical effectiveness was evaluated by analyzing between-group (control vs. display, periods 2 and 3) and within-group (display, period 1 vs. period 3) differences in time spent in high, low, and target (81-140 mg/dl) glucose zones. When prospective, real-time sensor values were compared with SMBG values, 95.4% of 6,767 paired glucose values fell within Clarke error grid A and B zones. Pearson's correlation coefficient was 0.88, and mean and median absolute relative differences were 21.2 and 15.9%, respectively. No systematic bias was detected at any of the prespecified glucose levels (50, 80, 100, 150, and 200 mg/dl). When compared with control subjects, the display group spent 21% less time as hypoglycemic (<55 mg/dl), 23% less time as hyperglycemic (> or = 240 mg/dl), and 26% more time in the target (81-140 mg/dl) glucose range (P < 0.001 for each comparison). Nocturnal (10:00 p.m. to 6:00 a.m.) hypoglycemia, as assessed at two thresholds, was also reduced by 38% (<55 mg/dl; P < 0.001) and 33% (55-80 mg/dl; P < 0.001) in the display group compared with control subjects. We conclude that real-time continuous glucose monitoring for periods up to 72 h is accurate and safe in insulin-requiring subjects with type 1 and type 2 diabetes. This study demonstrates that availability of real-time, continuously measured glucose levels can significantly improve glycemic excursions by reducing exposure to hyperglycemia without increasing the risk of hypoglycemia, which may reduce long-term diabetes complications and their associated economic costs.

Accuracy of Newer-Generation Home Blood Glucose Meters in a Diabetes Research in Children Network (DirecNet) Inpatient Exercise Study

The objective of this study was to assess how the accuracy of the FreeStyle Flash (Abbott Diabetes Care, Alameda, CA) meter compares with that of the One Touch Ultra (Lifescan, Milpitas, CA) home glucose meter (HGM). Fifty children with type 1 diabetes (T1D), 10-17 years old, were admitted for two separate 24-h periods to assess the effect of exercise on subsequent nocturnal hypoglycemia. Resulting data were used in a preplanned analysis of the accuracy of the Ultra and FreeStyle HGMs. Glucose levels were measured throughout the day and night and every 15-20 min during a standardized exercise protocol. Reference samples were assayed in a central laboratory using a hexokinase enzymatic method. These reference glucose measurements were paired with HGM values from venous blood obtained within +/- 5 min. The median relative absolute difference was 5% for both the Ultra and FreeStyle HGMs, and the percentages of pairs meeting the International Organisation for Standardization criteria were 99% and 98%, respectively. The FreeStyle tended to read slightly higher than the reference method (median difference = +3 mg/dL; P < 0.001), and there was trend in this direction for the Ultra (median difference = +2 mg/dL, P = 0.15). Sensitivities for detection of hypoglycemia (reference < or = 60 and HGM < or = 70 mg/dL) were 96% and 100% for the Ultra and FreeStyle, respectively, and corresponding false-positive rates were both 5%. In a controlled clinical setting using venous blood samples, both the Ultra and FreeStyle meters demonstrated a high degree of accuracy compared with the laboratory reference over a broad range of glucose concentrations in children with T1D.

Accuracy of the Modified Continuous Glucose Monitoring (CGMS®) Sensor in an Outpatient Setting: Results from a Diabetes Research in Children Network (DirecNet) Study

We previously reported the results of an inpatient accuracy study in children with type 1 diabetes using the Continuous Glucose Monitoring System (CGMS, Medtronic MiniMed, Northridge, CA). During the course of that study, a new process was implemented for manufacturing the CGMS sensor. Accuracy from the resulting modified sensor used by only 14 children was significantly better than the original version [median relative absolute difference (RAD), 11% vs. 19%; P < 0.001]. Baseline data from a subsequent outpatient study provide an opportunity to further assess the accuracy of the modified sensor in a much larger sample of children with type 1 diabetes. As part of a randomized trial to assess the utility of the GlucoWatch G2 Biographer (Cygnus, Inc., Redwood City, CA), 200 children with type 1 diabetes were instructed to wear a CGMS for 48-72 h in an outpatient setting at baseline. Glucose measurements from a OneTouch UltraSmart (Lifescan, Inc., Milpitas, CA) home glucose meter were downloaded and used as reference values to calculate accuracy measures. The overall median RAD was 12%. Accuracy was better during hyperglycemia than during hypoglycemia (median RAD, 10% vs. 20%; P < 0.001) and on optimal versus non-optimal days but did not vary significantly by the number of calibrations entered. These data confirm the improved accuracy previously reported for the modified version of the CGMS sensor.

A multicenter study of the accuracy of the One Touch Ultra home glucose meter in children with type 1 diabetes.

Data are not readily available on the accuracy of one of the most commonly used home blood glucose meters, the One Touch Ultra (LifeScan, Milpitas, California). The purpose of this report is to provide information on the accuracy of this home glucose meter in children with type 1 diabetes. During a 24-h clinical research center stay, the accuracy of the Ultra meter was assessed in 91 children, 3-17 years old, with type 1 diabetes by comparing the Ultra glucose values with concurrent reference serum glucose values measured in a central laboratory. The Pearson correlation between the 2,068 paired Ultra and reference values was 0.97, with the median relative absolute difference being 6%. Ninety-four percent of all Ultra values (96% of venous and 84% of capillary samples) met the proposed International Organisation for Standardisation (ISO) standard for instruments used for self-monitoring of glucose when compared with venous reference values. Ninety-nine percent of values were in zones A + B of the Modified Error Grid. A high degree of accuracy was seen across the full range of glucose values. For 353 data points during an insulin-induced hypoglycemia test, the Ultra meter was found to have accuracy that was comparable to concurrently used benchmark instruments (Beckman, YSI, or i-STAT); 95% and 96% of readings from the Ultra meter and the benchmark instruments met the proposed ISO criteria, respectively. These results confirm that the One Touch Ultra meter provides accurate glucose measurements for both hypoglycemia and hyperglycemia in children with type 1 diabetes.