Subcutaneous glucose sensor values closely parallel blood glucose during insulin-induced hypoglycaemia

Impedance-based polymer microneedle patch sensor for continuous interstitial fluid glucose monitoring

Early detection and effective blood glucose control are critical for preventing and managing diabetes-related complications. Conventional glucometers provide point-in-time measurements but are painful and cannot facilitate continuous monitoring. Continuous glucose monitoring systems are comfortable but face challenges in terms of accuracy, cost, and sensor lifespan. This study aimed to develop a microneedle-based sensor patch for minimally invasive, painless, and continuous glucose monitoring in the interstitial fluid to address these limitations. Experimental results confirm painless and minimally invasive penetration of the skin tissue with cylindrical microneedles (3 × 3 array) to a depth of approximately 520 μm with minimal loading. The microneedle sensors fabricated with precision using the complementary metal-oxide semiconductor process were immobilized with glucose oxidase, as confirmed through phase angle analysis. Long-term tests confirmed the effective operation of the sensor for up to seven days. Glucose concentrations determined from the fitted concentration-impedance curves correlated well with those measured using commercial glucometers, indicating the reliability and precision of the microneedle sensor. The flexible and minimally invasive sensor developed in this study facilitates painless and continuous glucose monitoring.

Glycemic response to acute high-intensity interval versus moderate-intensity continuous exercise during pregnancy

The present study investigated the glycemic response to an acute high-intensity interval training (HIIT) session (10 one-minute intervals ≥90% HRmax interspersed with one-minute of active recovery) versus a moderate-intensity continuous training (MICT) session (30 min at 64%-76% HRmax ) during pregnancy. Twenty-four normoglycemic females with a singleton pregnancy (27.8 ± 4.7 weeks of gestation, 31.5 ± 4.1 years of age, body mass index: 25.2 ± 11.3) participated in a randomized crossover design study. A flash glucose monitor and accelerometer were worn continuously for 7 days recording glycemic response, physical activity, and sleep. Nutritional intake and enjoyment of the exercise were self-reported. Average heart rate during exercise was higher for HIIT (82 ± 4% HRmax ) compared with MICT (74 ± 4% HRmax ; p < 0.001) and participants achieved a peak heart rate of 92 ± 3% during HIIT (range 85%-97% HRmax ) compared with 81 ± 4% during MICT (p < 0.001). The change in glucose values from pre-to-postexercise were not different between conditions (HIIT: -0.62 ± 1.00 mmol/L; MICT: -0.81 ± 1.05 mmol/L; p = 0.300) with the exception that fewer individuals experienced postexercise hypoglycemia immediately following HIIT compared with MICT (8% versus 33% respectively; p = 0.041). Other glucose variables was not different between exercise protocols. Physical activity (p = 0.07) and caloric intake did not differ (p = 0.10). The majority of participants preferred HIIT (87.5%) and had greater perceived enjoyment compared to MICT (HIIT: 7.8 ± 1.5; MICT: 6.6 ± 2.0; p = 0.015). Sleep duration was 52 ± 73 min longer after participating in HIIT compared with the night prior (main effect for time p = 0.017); no significant changes for MICT. Overall, an acute session of HIIT appears to be well tolerated and demonstrates no adverse effects on maternal glycemic response.

Discordance Between Glucose Levels Measured in Interstitial Fluid vs in Venous Plasma After Oral Glucose Administration: A Post-Hoc Analysis From the Randomised Controlled PRE-D Trial

AIMS

The oral glucose tolerance test (OGTT) is together with haemoglobin A_1c (HbA_1c) gold standard for diagnosing prediabetes and diabetes. The objective of this study was to assess the concordance between glucose values obtained from venous plasma versus interstitial fluid after oral glucose administration in 120 individuals with prediabetes and overweight/obesity.

METHODS

120 adults with prediabetes defined by HbA_1c 39-47 mmol/mol and overweight or obesity who participated in the randomised controlled PRE-D trial were included in the study. Venous plasma glucose concentrations were measured at 0, 30, 60 and 120 minutes during a 75 g oral glucose tolerance test (OGTT) performed on three different occasions within a 26 weeks period. During the OGTT, the participants wore a CGM device (IPro2, Medtronic), which assessed glucose concentrations every five minutes.

RESULTS

A total of 306 OGTTs with simultaneous CGM measurements were obtained. Except in fasting, the CGM glucose values were below the OGTT values throughout the OGTT period with mean (SD) differences of 0.2 (0.7) mmol/L at time 0 min, -1.1 (1.3) at 30 min, -1.4 (1.8) at 60 min, and -0.5 (1.1) at 120 min). For measurements at 0 and 120 min, there was a proportional bias with an increasing mean difference between CGM and OGTT values with increasing mean of the two measurements.

CONCLUSIONS

Due to poor agreement between the OGTT and CGM with wide 95% limits of agreement and proportional bias at 0 and 120 min, the potential for assessing glucose tolerance in prediabetes using CGM is questionable.

Continuous glucose monitoring for hypoglycaemia in children: Perspectives in 2020

Hypoglycaemia in children is a major risk factor for adverse neurodevelopment with rates as high as 50% in hyperinsulinaemic hypoglycaemia (HH). A key part of management relies upon timely identification and treatment of hypoglycaemia. The current standard of care for glucose monitoring is by infrequent fingerprick plasma glucose testing but this carries a high risk of missed hypoglycaemia identification. High-frequency Continuous Glucose Monitoring (CGM) offers an attractive alternative for glucose trend monitoring and glycaemic phenotyping but its utility remains largely unestablished in disorders of hypoglycaemia. Attempts to determine accuracy through correlation with plasma glucose measurements using conventional methods such as Mean Absolute Relative Difference (MARD) overestimate accuracy at hypoglycaemia. The inaccuracy of CGM in true hypoglycaemia is amplified by calibration algorithms that prioritize hyperglycaemia over hypoglycaemia with minimal objective evidence of efficacy in HH. Conversely, alternative algorithm design has significant potential for predicting hypoglycaemia to prevent neuroglycopaenia and consequent brain dysfunction in childhood disorders. Delays in the detection of hypoglycaemia, alarm fatigue, device calibration and current high cost are all barriers to the wider adoption of CGM in disorders of hypoglycaemia. However, machine learning, artificial intelligence and other computer-generated algorithms now offer significant potential for further improvement in CGM device technology and widespread application in childhood hypoglycaemia.

A Feasibility Study to Detect Neonatal Hypoglycemia in Infants of Diabetic Mothers Using Real-Time Continuous Glucose Monitoring

BACKGROUND

Infants born to mothers with diabetes commonly experience asymptomatic hypoglycemia after birth. Continuous glucose monitors (CGM) can detect asymptomatic hypoglycemia in this population without the need for painful glucose checks.

METHODS

Infants born after 34 weeks of gestation to mothers with diabetes had a CGM placed after birth. One group of infants was remotely monitored in real-time by research staff during the hospitalization, whereas another group wore a blinded CGM. In both groups, hospital standard-of-care (SOC) glucose checks were performed. Clinical staff and families were blinded to CGM data. For CGM readings <45 mg/dL, research staff requested a verification blood glucose (BG) using the point-of-care glucometer.

RESULTS

Sixteen infants were studied; 4 with a blinded CGM and 12 with remote monitoring (RM). When there were confirmatory hospital glucometer readings, the sensitivity of the CGM to detect hypoglycemia was 86% and the specificity was 91%. The positive predictive value was 55% and the negative predictive value was 98%. In the full cohort, hypoglycemia (<45 mg/dL) was confirmed in 12 of 16 infants with 30 events at <12 hours of life (HOL), 3 events between 12 and 24 HOL, and 1 event at >48 HOL. In the RM group, CGM detected hypoglycemia five times when the infant was not due for a BG check based on the SOC. Overall, the CGM detected five false-positive alerts and six true-positive alerts for hypoglycemia. Only one hypoglycemic episode was missed by CGM in the RM group. Barriers to recruitment included fear of pain with glucose checks, concerns with CGM use, satisfaction with the hospital SOC, personal reasons independent of the study, and lack of interest in participating in research.

CONCLUSIONS

Although there were barriers to recruitment and retention in the study, we conclude that CGM can provide added benefit for detecting hypoglycemia when used early after birth.

Higher blood glucose and larger fluctuations detected postoperatively using continuous glucose monitoring: a preliminary study following total knee or hip arthroplasty

BACKGROUND

The control of diabetes mellitus (DM) should help reduce the incidence of periprosthetic joint infection (PJI). Self-monitoring of blood glucose (SMBG) concentration is usually undertaken at fixed time-points. Therefore, the extent of postoperative blood glucose fluctuation might be underestimated. To provide a more comprehensive assessment, continuous glucose monitoring (CGM) is beginning to be used. However, no previous studies have evaluated blood glucose concentrations using CGM following orthopedic surgery. Therefore, the differences between the maximum blood glucose concentrations measured using SMBG and CGM, and the mean amplitude of the glycemic fluctuation in patients with frank diabetes mellitus (DM) or pre-diabetes were evaluated. Blood glucose was measured in 20 patients who had undergone total hip or total knee arthroplasty (12 patients with DM and eight with pre-diabetes). Patients were fitted with a CGM device in the operating room, which was worn for 6 days postoperatively, and used to evaluate blood glucose concentration continuously. SMBG was performed simultaneously for the same period.

RESULTS

The mean difference between the maximum blood glucose concentrations measured using SMBG and CGM was 25.0 ± 20.3 mg/dl (range, - 17 to 81 mg/dl), with the concentrations measured using CGM tending to be higher than those measured using SMBG (P = 0.04). Blood glucose concentrations measured using CGM tended to be higher than those measured using SMBG until postoperative day 2, and to decrease gradually after postoperative day 4. There were no significant differences in the standard deviation of the blood glucose concentrations between the two groups.

CONCLUSIONS

Blood glucose concentrations > 200 mg/dl and larger fluctuations were more frequently recorded using CGM than SMBG, especially until postoperative day 2. Thus, CGM is more useful for the identification of high blood glucose concentrations and larger fluctuations. However, this information was not provided in real time.

Plasma Insulin Levels and Hypoglycemia Affect Subcutaneous Interstitial Glucose Concentration

BACKGROUND

Continuous glucose monitoring (CGM) accuracy during hypoglycemia is suboptimal. This might be partly explained by insulin or hypoglycemia-induced changes in the plasma interstitial subcutaneous (SC) fluid glucose gradient. The aim of the present study was to assess the role of plasma insulin (PI) and hypoglycemia itself in the plasma and interstitial SC fluid glucose concentration in patients with type 1 diabetes mellitus.

METHODS

Eleven subjects with type 1 diabetes (age 36.5 ± 9.1 years, HbA_1c 7.9 ± 0.4% [62.8 ± 2.02 mmol/mol]; mean ± standard deviation) were evaluated under hyperinsulinemic euglycemia and hypoglycemia. Each subject underwent two randomized crossover clamps with either a primed 0.3 (low insulin) or 1 mU/(kg·min) (high insulin) insulin infusion. The raw CGM signal was normalized with median preclamp values to obtain a standardized measure of the interstitial glucose (IG) concentration before statistical analysis.

RESULTS

The mean PI concentration was greater in high insulin studies (HISs) versus low insulin studies (LISs) (412.89 ± 13.63 vs. 177.22 ± 10.05 pmol/L). During hypoglycemia, glucagon, adrenaline, free fatty acids, glycerol, and beta-OH-butyrate were higher in the LIS (P < 0.0001). Likewise, the IG concentration was significantly different (P < 0.0001). This was due to lower IG concentration than plasma glucose (PG) concentration during the euglycemic hyperinsulinemic phases in the HIS. In contrast, no difference was observed during hypoglycemia. This was the result of an unchanged PG/IG gradient during the entire LIS, while in the HIS, this gradient increased during the hyperinsulinemic euglycemia phase.

CONCLUSION

Both PI levels and hypoglycemia affect the relationship between IG and PG concentration. ClinicalTrials.gov Identifier: NCT01714895.

Continuous Glucose Monitoring After Gastric Bypass to Evaluate the Glucose Variability After a Low-Carbohydrate Diet and to Determine Hypoglycemia

BACKGROUND

Roux-en-Y gastric bypass (RYGB) alters glucose metabolism and can cause postprandial hypoglycemia. Continuous glucose monitoring (CGM) has been proposed as an evaluation tool in hypoglycemic RYGB individuals. The objective of this study is to investigate the use of CGM in clinical decision-making including diagnosing hypoglycemia and evaluating treatment effects. Furthermore, we aim to assess its accuracy in RYGB-operated individuals.

METHODS

Thirteen RYGB individuals with symptomatic hypoglycemia and 13 asymptomatic RYGB individuals underwent CGM for 5 days. During this period, a mixed-meal test with concomitant plasma glucose (PG) measurements was performed. Furthermore, the RYGB individuals followed a low-carbohydrate diet (LCD) for 1 day and maintained their ordinary diet (OD) for the rest of the period.

RESULTS

LCD reduced the CGM-determined glycemic variability of the mean interstitial fluid glucose (IFG) significantly compared to OD (p < 0.0001). Receiver operating characteristic analysis confirmed that low blood glucose index (e.g., the frequency and amplitude of hypoglycemic events) is the most reliable parameter related to the development of symptomatic hypoglycemia, with a sensitivity of 0.91 (confidence interval [CI] 0.59; 1.00) and a specificity of 0.77 (CI 0.46; 0.95). However, CGM, measuring the IFG in the subcutaneous adipose tissue, overestimated the minimum glucose levels by 1.1 ± 0.9 mmol/l compared with PG.

CONCLUSIONS

CGM was a good method for demonstrating increased glycemic variability among RYGB individuals and for displaying dietary effects on reducing this glycemic variability, including hypoglycemic events. In RYGB individuals, CGM-measured IFG overestimated the real glucose value by about 1 mmol/l in the hypoglycemic range. This should be taken into consideration if CGM is used to diagnose hypoglycemia after RYGB.

The value of real-time continuous glucose monitoring in premature infants of diabetic mothers

To determine the feasibility of using a real-time continuous glucose monitoring system (RTGMS) in intensive care units, our study focus on preterm infants with diabetic mothers owing to their high risk of blood sugar abnormalities. Thirty preterm babies (M = 15 and F = 15; ≤ 36 week gestation age) were studied from within 72 hours of delivery. These babies were admitted to the newborn intensive care and were further categorized into groups based on whether their mothers with or without diabetic mellitus. Blood sugar levels were monitored by both RTGMS and the traditional intermittent arterial line (A-Line) glucose method. Continuous glucose monitoring were well tolerated in 30 infants. There were good consistency between RTGMS and A-Line glucose concentration measurements. Of the preterm infants, 33.33% experienced abnormal glucose levels (hypoglycemia or hyperglycemia) between the checkpoint intervals of the intermittent A-Line blood sugar measurements. RTGM showed advantages with regards to reduced pain, greater comfort, the provision of real-time information, high sensitivity (94.59%) and specificity (97.87%) in discovering abnormalities of blood sugar, which are especially valuable for premature infants of diabetic mothers. RTGMS is comparable to A-line measurement for identifying fluctuations in blood glucose in premature infants. RTGMS detects more episodes of abnormal glucose concentration than intermittent A-line blood glucose measurement. High risk infants, especially premature infants with diabetic mothers, should receive more intensive blood sugar level checks by using continuous RTGMS.

A comparison of adipose tissue interstitial glucose and venous blood glucose during postprandial resistance exercise in patients with type 2 diabetes

Resistance exercise during the postprandial period lowers venous glucose concentrations in individuals with type 2 diabetes, but the impact of resistance exercise on interstitial glucose concentrations is not well understood. The objective of this study was to compare subcutaneous adipose tissue interstitial glucose and venous blood glucose concentrations during postprandial resistance exercise in patients with type 2 diabetes. Eleven individuals completed two trials in a random order including a no-exercise (NoEx) and a postprandial resistance exercise trial (M-Ex). During the trials, the individuals consumed a meal and either remained sedentary (NoEx) or performed a session of resistance training beginning 45 min after the meal (M-Ex) while interstitial and venous glucose concentrations were simultaneously measured. Venous glucose during exercise was ~11% lower ( P = 0.05) during M-Ex (8.0 ± 0.5 mmol/l) compared with NoEx (9.0 ± 0.5 mmol/l) whereas interstitial glucose during M-Ex (10.4 ± 0.7 mmol/l) was not different compared with interstitial glucose during NoEx (10.1 ± 0.7 mmol/l). Bland-Altman plots revealed that the difference (bias) between interstitial and venous glucose during exercise was more than twofold greater during M-Ex (2.36 ± 2.07 mmol/l) compared with NoEx (1.11 ± 1.69 mmol/l). The mean (33.8 ± 6.2 mmol/l) and median (34.7 ± 6.3 mmol/l) absolute relative difference during exercise were 73% and 78% greater compared with the mean (19.5 ± 4.1 mmol/l) and median (19.5 ± 4.1 mmol/l) absolute relative difference during NoEx ( P = 0.04). Resistance exercise has unequal effects on glucose concentrations within different bodily compartments as exercise reduced venous glucose concentrations but not adipose tissue interstitial glucose concentrations in the abdominal region in individuals with type 2 diabetes. NEW & NOTEWORTHY This is the first study to compare subcutaneous adipose tissue interstitial glucose concentrations and venous blood glucose concentrations during postprandial resistance exercise in individuals with type 2 diabetes. We find that resistance exercise effectively reduces systemic venous blood glucose concentrations but not subcutaneous adipose tissue interstitial glucose concentrations in the abdominal region. Resistance exercise has differential effects on glucose concentrations depending on its compartmentalization within the body.

Continuous determination of blood glucose in children admitted with malaria in a rural hospital in Mozambique

Background

Hypoglycaemia is a frequent complication among admitted children, particularly in malaria-endemic areas. This study aimed to estimate the occurrence of hypoglycaemia not only upon admission but throughout the first 72 h of hospitalization in children admitted with malaria.

Methods

A simple pilot study to continuously monitor glycaemia in children aged 0–10 years, admitted with malaria in a rural hospital was conducted in Southern Mozambique by inserting continuous glucose monitors (CGMs) in subcutaneous tissue of the abdominal area, producing glycaemia readings every 5 min.

Results

Glucose was continuously monitored during a mean of 48 h, in 74 children. Continuous measurements of blood glucose were available for 72/74 children (97.3%). Sixty-five of them were admitted with density-specific malaria diagnosis criteria (17 severe, 48 uncomplicated). Five children (7.7%) had hypoglycaemia (<54 mg/dL) on admission as detected by routine capillary determination. Analysing the data collected by the CGMs, hypoglycaemia episodes (<54 mg/dL) were detected in 10/65 (15.4%) of the children, of which 7 (10.8%) could be classified as severe (≤45 mg/dL). No risk factors were independently associated with the presence of at least one episode of hypoglycaemia (<54 mg/dL) during hospitalization. Only one death occurred among a normoglycaemic child. All episodes of hypoglycaemia detected by CGMs were subclinical episodes or not perceived by caregivers or clinical staff.

Conclusions

Hypoglycaemia beyond admission in children with malaria appears to be much more frequent than what had been previously described. The clinical relevance of these episodes of hypoglycaemia in the medium or long term remains to be determined.

Esophageal and Gastric Dysmotilities are Associated with Altered Glucose Homeostasis and Plasma Levels of Incretins and Leptin

BACKGROUND

Gastrointestinal complications in diabetes may affect glucose and endocrine homeostasis. Glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1), and leptin regulate glucose homeostasis, food intake, and gastric emptying.

AIM

The aim was to investigate associations between diabetes complications and glucose homeostasis and plasma levels of GIP, GLP-1, and leptin.

METHODS

Sixteen diabetes patients (seven men) were examined with gastric emptying scintigraphy and 72-h continuous subcutaneous glucose monitoring, 14 with the deep-breathing test, and 12 with esophageal manometry. A fiber-rich breakfast was given during the second day of glucose registration. Blood samples were taken 10 min and right before a fat-rich breakfast, as well as 10, 20, 30, 45, 60, 90, 120, 150, and 180 min afterwards. 20 healthy volunteers acted as controls. Plasma was analyzed regarding GIP, GLP-1, and leptin by Luminex.

RESULTS

Gastroparesis lowered maximal concentration (c-max) (p = 0.003) and total area under the curve (tAUC) (p = 0.019) of glucose levels as well as d-min (p = 0.043) of leptin levels. It tended to lower baseline (p = 0.073), c-max (p = 0.066), change from baseline (d-max) (p = 0.073), and tAUC (p = 0.093) of GLP-1 concentrations. Esophageal dysmotility tended to lower tAUC of glucose levels (p = 0.063), and c-min (p = 0.065) and tAUC (p = 0.063) of leptin levels. Diabetes patients had a higher baseline concentration of glucose (p = 0.013), GIP (p = 0.023), and leptin (p = 0.019) compared with healthy subjects.

CONCLUSIONS

Gastric and esophageal dysmotility are associated with both lesser increases in postprandial glucose elevations and decreased postprandial changes in GLP-1 and leptin.

Continuous glucose monitoring in preterm infants: evaluation by a modified Clarke error grid

Background

Continuous glucose monitoring using subcutaneous sensors has been validated in adults and children with diabetes, and was found to be useful in the management of glucose control. We aimed to assess feasibility and reliability of a new continuous glucose monitoring system (CGMS) in a population of preterm neonates using a Clarke error grid (CEG) specifically modified for preterm infants.

Methods

Preterm infants were recruited within 24 h from delivery. A subcutaneous sensor connected to a CGMS was inserted and maintained for 6 days. Data collected from CGMS were compared with data obtained using a glucometer. Management of the infants followed standard protocols and was not influenced by CGMS readings.

Results

Twenty patients (9 males) were included. Median (range) gestational age was 32 weeks (27–36) and median (range) birth weight was 1350 g (860–3360). Average CGMS recording time was 137 h, for a total of 449 paired glucose levels. CEG and modified CEG criteria for clinical significance were met.

Conclusion

CGMS is a safe and clinically adequate method to estimate glucose levels in preterm infants. As the glucose level can be evaluated in real time, this CGMS could be useful to reduce the number of heel sticks, to observe glycaemic trends and to promptly detect episodes of both hypo- and hyper-glycaemia.

Spectroscopic approach for dynamic bioanalyte tracking with minimal concentration information

Vibrational spectroscopy has emerged as a promising tool for non-invasive, multiplexed measurement of blood constituents - an outstanding problem in biophotonics. Here, we propose a novel analytical framework that enables spectroscopy-based longitudinal tracking of chemical concentration without necessitating extensive a priori concentration information. The principal idea is to employ a concentration space transformation acquired from the spectral information, where these estimates are used together with the concentration profiles generated from the system kinetic model. Using blood glucose monitoring by Raman spectroscopy as an illustrative example, we demonstrate the efficacy of the proposed approach as compared to conventional calibration methods. Specifically, our approach exhibits a 35% reduction in error over partial least squares regression when applied to a dataset acquired from human subjects undergoing glucose tolerance tests. This method offers a new route at screening gestational diabetes and opens doors for continuous process monitoring without sample perturbation at intermediate time points.

Interstitium versus Blood Equilibrium in Glucose Concentration and its Impact on Subcutaneous Continuous Glucose Monitoring Systems

The relationship between both interstitial and blood glucose remains a debated topic, on which there is still no consensus. The experimental evidence suggests that blood and interstitial fluid glucose levels are correlated by a kinetic equilibrium, which as a consequence has a time and magnitude gradient in glucose concentration between blood and interstitium. Furthermore, this equilibrium can be perturbed by several physiological effects (such as foreign body response, wound-healing effect, etc.), with a consequent reduction of interstitial fluid glucose versus blood glucose correlation. In the present study, the impact of operating in the interstitium on continuous glucose monitoring systems (CGMs) will be discussed in depth, both for the application of CGMs in the management of diabetes and in other critical areas, such as tight glycaemic control in critically ill patients.

Microdialysis-coupled enzymatic microreactor for in vivo glucose monitoring in rats

Continuous glucose monitoring (CGM) is an important aid for diabetic patients to optimize glycemic control and to prevent long-term complications. However, current CGM devices need further miniaturization and improved functional performance. We have coupled a previously described microfluidic chip with enzymatic microreactor (EMR) to a microdialysis probe and evaluated the performance of this system for monitoring subcutaneous glucose concentration in rats. Nanoliter volumes of microdialysis sample are efficiently reacted with continuously supplied glucose oxidase (GOx) solution in the EMR. The hydrogen peroxide produced is amperometrically detected at a (polypyrrole (PPy)-protected) thin-film Pt electrode. Subcutaneous glucose concentration was continuously monitored in anesthetized rats in response to intravenous injections of 20% glucose (w/v), 5 U/kg insulin, or saline as a control. In vitro evaluation showed a linear range of 2.1-20.6 mM and a sensitivity of 7.8 ± 1.0 nA/mM (n = 6). The physical lag time between microdialysis and the analytical signal was approximately 18 min. The baseline concentration of blood glucose was 10.2 ± 2.3 mM. After administering glucose to the rats, glucose levels increased by about 2 mM to 12.1 ± 2.3 mM in blood and 11.9 ± 1.5 mM in subcutaneous interstitial fluid (ISF). After insulin administration, glucose levels decreased by about 8 mM relative to baseline to 2.1 ± 0.6 mM in blood and 2.1 ± 0.9 mM in ISF. A microfluidic device with integrated chaotic mixer and EMR has been successfully combined with subcutaneous microdialysis to continuously monitor glucose in rats. This proof-of-principle demonstrates the feasibility of improved miniaturization in CGM based on microfluidics.

Evaluation of a continuous glucose monitoring system compared with an in-house standard laboratory assay and a handheld point-of-care glucometer in critically ill neonatal foals

OBJECTIVE

To evaluate the applicability and accuracy of a continuous glucose monitoring system (CGMS) in critically ill foals by comparing the performance of the CGMS, a point-of-care (POC) glucometer, and an in-house standard laboratory assay (SLA).

DESIGN

Prospective study.

SETTING

University teaching hospital.

ANIMALS

Seven critically ill neonatal foals requiring intensive care.

INTERVENTIONS

Foals were instrumented with a CGMS that measured interstitial glucose concentration every 5 minutes for the duration of 15-79 hours. Capillary and venous blood samples were taken every 4-6 hours for POC and SLA measurements, respectively.

MEASUREMENTS AND MAIN RESULTS

Bland-Altman analysis showed a mean bias (95% limits of agreement) of -0.1 (-3.9 to 3.5) mmol/L for comparison of CGMS versus SLA, 0.06 (-3.9 to 4.0) mmol/L for comparison of CGMS versus POC glucometer, and -0.16 (-1.8 to 1.5) mmol/L for comparison of POC glucometer versus SLA. Percent agreement and weighted kappa for classification in hypoglycemia, normoglycemia, and hyperglycemia were 68.4% and 0.296 for CGMS versus SLA, 72.4% and 0.442 for CGMS versus POC glucometer, and 80.7% and 0.568 for POC glucometer versus SLA.

CONCLUSIONS

The CGMS may be helpful for monitoring a trend in interstitial glucose concentration in critically ill neonatal foals. However, considering the wide limits of agreement between methods, the CGMS should only be used as an adjunctive device to other, more accurate and readily available methods that are able to detect acute changes in glucose concentration. Its use is further limited by the relatively high costs of the sensors, the mandatory 2-hour initialization period, and the difficulties of keeping the transducer in place in an active foal. The POC glucometer used in this study is easy to use and proved to be sufficiently accurate for repeated, stall-sided glucose monitoring in neonatal foals.

Point accuracy of interstitial continuous glucose monitoring during exercise in type 1 diabetes

BACKGROUND

Previous studies of aerobic exercise have found lower sensor accuracy during exercise. Whether or not resistance exercise would also be associated with lower sensor accuracy has not yet been examined. This study sought to investigate the accuracy of continuous glucose monitoring sensor values at rest, during aerobic exercise, and during resistance exercise.

SUBJECTS AND METHODS

Twelve individuals with type 1 diabetes performed 45 min of aerobic exercise, resistance exercise, or no exercise/rest followed by 60 min of recovery while monitored by continuous glucose monitoring systems.

RESULTS

Sensors underestimated plasma glucose to the greatest extent during rest (-1.29 ± 1.39 mmol/L, P<0.001) and resistance exercise (-0.71 ± 1.35 mmol/L, P<0.001) and least during aerobic exercise (-0.11 ± 1.71 mmol/L, P=0.416).

CONCLUSIONS

Optimal accuracy observed with aerobic exercise might arise from augmented blood flow better equilibrating plasma and interstitial fluid or from the combination of systematic sensor underestimation and sensor lag time.

Influence of time point of calibration on accuracy of continuous glucose monitoring in individuals with type 1 diabetes

BACKGROUND AND AIMS

Data on the influence of calibration on accuracy of continuous glucose monitoring (CGM) are scarce. The aim of the present study was to investigate whether the time point of calibration has an influence on sensor accuracy and whether this effect differs according to glycemic level.

SUBJECTS AND METHODS

Two CGM sensors were inserted simultaneously in the abdomen on either side of 20 individuals with type 1 diabetes. One sensor was calibrated predominantly using preprandial glucose (calibration(PRE)). The other sensor was calibrated predominantly using postprandial glucose (calibration(POST)). At minimum three additional glucose values per day were obtained for analysis of accuracy. Sensor readings were divided into four categories according to the glycemic range of the reference values (low, ≤4 mmol/L; euglycemic, 4.1-7 mmol/L; hyperglycemic I, 7.1-14 mmol/L; and hyperglycemic II, >14 mmol/L).

RESULTS

The overall mean±SEM absolute relative difference (MARD) between capillary reference values and sensor readings was 18.3±0.8% for calibration(PRE) and 21.9±1.2% for calibration(POST) (P<0.001). MARD according to glycemic range was 47.4±6.5% (low), 17.4±1.3% (euglycemic), 15.0±0.8% (hyperglycemic I), and 17.7±1.9% (hyperglycemic II) for calibration(PRE) and 67.5±9.5% (low), 24.2±1.8% (euglycemic), 15.5±0.9% (hyperglycemic I), and 15.3±1.9% (hyperglycemic II) for calibration(POST). In the low and euglycemic ranges MARD was significantly lower in calibration(PRE) compared with calibration(POST) (P=0.007 and P<0.001, respectively).

CONCLUSIONS

Sensor calibration predominantly based on preprandial glucose resulted in a significantly higher overall sensor accuracy compared with a predominantly postprandial calibration. The difference was most pronounced in the hypo- and euglycemic reference range, whereas both calibration patterns were comparable in the hyperglycemic range.

Relationship between interstitial and blood glucose during hypoglycemia in subjects with type 2 diabetes

BACKGROUND

Continuous glucose monitoring devices measure interstitial glucose and are commonly used to investigate hypoglycemia. The relationship between interstitial glucose and blood glucose is not completely understood, particularly at low blood glucose concentrations. Interstitial glucose during hypoglycemia is generally lower than blood glucose in young subjects without diabetes and those with type 1 diabetes, but the effect of insulin resistance and obesity in type 2 diabetes on this relationship has not been examined previously. We studied the relationship between blood and interstitial glucose during experimental hypoglycemia in subjects with type 2 diabetes treated with insulin or sulfonylureas and matched controls without diabetes.

METHODS

Twenty subjects with type 2 diabetes (10 sulfonylurea-treated and 10 insulin-treated) and 10 controls without diabetes of similar age and weight underwent stepped hyperinsulinemic hypoglycemic clamps. We compared blood and interstitial glucose at different levels of hypoglycemia using random effects modeling.

RESULTS

Interstitial glucose was significantly higher than blood glucose at all levels of hypoglycemia (P<0.001), and this difference increased as glucose fell. For every 1 mmol/L drop in blood glucose, the difference increased by 0.32 mmol/L (P<0.001). This difference was not affected by presence of type 2 diabetes or by modality of treatment (P=0.10).

CONCLUSIONS

In older subjects with or without type 2 diabetes, interstitial glucose is significantly higher than blood glucose, and this difference increases with increasing severity of hypoglycemia. Continuous glucose monitors may underestimate hypoglycemia in this group, and this should be taken into account when interpreting results obtained using this technology.

Glucose response of near-infrared alginate-based microsphere sensors under dynamic reversible conditions

BACKGROUND

Minimally invasive optical glucose biosensors with increased functional longevity form one of the most promising techniques for continuous glucose monitoring, because of their long-term stability, reversibility, repeatability, specificity, and high sensitivity. They are based on the principle of competitive binding and fluorescence resonance energy transfer. Moving to the near-infrared region of the spectrum has the potential to improve signal throughput for implanted sensors, but requires a change in dye chemistry that could alter response sensitivity, range, and toxicity profiles.

METHODS

The near-infrared dissolved-core alginate microsphere sensors were fabricated by emulsion followed by surface coating by layer-by-layer self-assembly. The particles were characterized for sensor stability, sensor response, and reversibility in deionized water and simulated interstitial fluid. The sensor response to step changes in bulk glucose concentrations was also evaluated under dynamic conditions using a microflow cell unit. Finally, in vitro cytotoxicity assays were performed with L929 mouse fibroblast cell lines to demonstrate preliminary biocompatibility of the sensors.

RESULTS

The glucose sensitivity under controlled and dynamic conditions was observed to be 0.86%/mM glucose with an analytical response range of 0-30 mM glucose, covering both the physiological and pathophysiological range. The sensor demonstrated a repeatable, reversible, and reproducible response, with a maximum response time of 120 s. In vitro cytotoxicity assays revealed nearly 95% viability of cells, thereby suggesting that the alginate microsphere sensor system does not exhibit cytotoxicity.

CONCLUSIONS

The incorporation of near-infrared dyes shows promise in improving sensor response because of their high sensitivity and improved tissue penetration of infrared light. The sensitivity for the sensors was approximately 1.5 times greater than that observed for visible dye sensors, and the new dye chemistry did not significantly alter the biocompatibility of the materials. These findings provide additional support for the potential application of alginate microspheres and similar systems such as "smart-tattoo" glucose sensors.

Prevalence of nocturnal hypoglycemia in pediatric type 1 diabetes: a pilot study using continuous glucose monitoring

OBJECTIVES

To determine the prevalence of nocturnal hypoglycemia (NH) in pediatric type 1 diabetes, to compare the prevalence of NH detected by continuous glucose monitoring (CGM) and self-monitored blood glucose (SMBG), and to compare the prevalence of NH using different thresholds.

STUDY DESIGN

Twenty-five patients wore a continuous glucose monitor for 3 nights and also conducted SMBG. NH was defined with three thresholds: (1) <3.9 mmol/L; (2) <3.3 mmol/L; and (3) <2.9 mmol/L.

RESULTS

The prevalence of NH with CGM was 68%, 52%, and 48% with the different thresholds. Of the 35 episodes of NH detected by CGM, 25 were not symptomatic and therefore not detected by SMBG. The mean difference in blood glucose between CGM and SMBG was -0.18 mmol/L (P = .35).

CONCLUSIONS

This pilot study suggests that the prevalence of NH in pediatric patients with type 1 diabetes with conventional treatment may be as high as 68%, although this varied according to the method of detection and threshold used. Patients may benefit from CGM to detect asymptomatic NH.

Hypoglycemia impairs quality of blood glucose simulation in a clinical decision support system

BACKGROUND

Clinical decision support systems allow for decisions based on blood glucose simulations. The DiasNet simulation tool is based on accepted principles of physiology and simulates blood glucose concentrations accurately in type 1 diabetes mellitus (T1DM) patients during periods without hypoglycemia, but deviations appear after hypoglycemia, possibly because of the long-term glucose counter-regulation to hypoglycemia. The purpose of this study was to evaluate the impact of hypoglycemia on blood glucose simulations.

METHOD

Continuous glucose monitoring (CGM) data and diary data (meals, insulin, self-monitored blood glucose) were collected for 2 to 5 days from 17 T1DM patients with poor glycemic control. Hypoglycemic episodes [CGM glucose <63 mg/dl (3.5 mmol/liter) for ≥20 min] were identified in valid (well-calibrated) CGM data. For 24 hours after each hypoglycemic episode, a simulated (DiasNet) glucose profile was compared to the CGM glucose.

RESULTS

A total of 52 episodes of hypoglycemia were identified in valid data. All subjects had at least one hypoglycemic episode. Ten episodes of hypoglycemia from nine subjects were eligible for analysis. The CGM glucose was significantly (p < .05) higher than simulated blood glucose for a period of 13 h, beginning 8 h after hypoglycemia onset.

CONCLUSIONS

The present data show that hypoglycemia introduces substantial and systematic simulation errors for up to 24 h after hypoglycemia. This underlines the need for further evaluation of mechanisms behind this putative long-term glucose counter-regulation to hypoglycemia. When using blood glucose simulations in decision support systems, the results indicate that simulations for several hours following a hypoglycemic event may underestimate glucose levels by 100 mg/dl (5.6 mmol/liter) or more.

"Smart tattoo" glucose biosensors and effect of coencapsulated anti-inflammatory agents

BACKGROUND

Minimally invasive glucose biosensors with increased functional longevity form one of the most promising techniques for continuous glucose monitoring. In the present study, we developed a novel nanoengineered microsphere formulation comprising alginate microsphere glucose sensors and anti-inflammatory-drug-loaded alginate microspheres.

METHODS

The formulation was prepared and characterized for size, shape, in vitro drug release, biocompatibility, and in vivo acceptability. Glucose oxidase (GOx)- and Apo-GOx-based glucose sensors were prepared and characterized. Sensing was performed both in distilled water and simulated interstitial body fluid. Layer-by-layer self-assembly techniques were used for preventing drug and sensing chemistry release. Finally, in vivo studies, involving histopathologic examination of subcutaneous tissue surrounding the implanted sensors using Sprague-Dawley rats, were performed to test the suppression of inflammation and fibrosis associated with glucose sensor implantation.

RESULTS

The drug formulation showed 100% drug release with in 30 days with zero-order release kinetics. The GOx-based sensors showed good enzyme retention and enzyme activity over a period of 1 month. Apo-GOx-based visible and near-infrared sensors showed good sensitivity and analytical response range of 0-50 mM glucose, with linear range up to 12 mM glucose concentration. In vitro cell line studies proved biocompatibility of the material used. Finally, both anti-inflammatory drugs were successful in controlling the implant-tissue interface by suppressing inflammation at the implant site.

CONCLUSION

The incorporation of anti-inflammatory drug with glucose biosensors shows promise in improving sensor biocompatibility, thereby suggesting potential application of alginate microspheres as "smart tattoo" glucose sensors with increased functional longevity.

Effect of short-term use of a continuous glucose monitoring system with a real-time glucose display and a low glucose alarm on incidence and duration of hypoglycemia in a home setting in type 1 diabetes mellitus

BACKGROUND

The objective of this study was to examine whether setting the low glucose alarm of a Guardian® REAL-Time continuous glucose monitoring system (CGMS) to 80 mg/dl for 3 days and providing instructions to users reduce the risk of hypoglycemia under free-living conditions in individuals with type 1 diabetes mellitus (T1DM).

METHODS

Fourteen participants with T1DM aged 26.1±6.0 years (mean±standard deviation) were fitted with a CGMS and assigned for 3 days to either an alarm [low and high blood glucose (BG) alarms set at 80 and 200 mg/dl, respectively] or no alarm condition, with each treatment administered to all participants following a counterbalanced design. All participants were given detailed instructions on how to respond appropriately to low glucose alarms.

RESULTS

The CGMS with alarm reduced the incidence of hypoglycemia (CGMS readings≤65 mg/dl) by 44% as well as the time spent below this hypoglycemic threshold by 64% without increasing average BG levels. However, the CGMS with alarm had no effect on the incidence of symptomatic hypoglycemia.

CONCLUSIONS

Short-term use of the CGMS with alarm, together with appropriate instructions for users, reduces the incidence and duration of hypoglycemia, but only to a limited extent, in part because it overestimates BG in the low glucose range.

Contribution of an intrinsic lag of continuous glucose monitoring systems to differences in measured and actual glucose concentrations changing at variable rates in vitro

BACKGROUND

Current continuous glucose monitoring (CGM) systems measure glucose levels in the interstitial fluid to estimate blood glucose concentration. A lag time has been observed between CGM system glucose readings and blood glucose levels when glucose levels are changing. Although this lag has been attributed to the time it takes glucose to equilibrate between blood and interstitial fluid compartments, it is unclear to what extent these inaccuracies reflect an intrinsic delay of the device itself.

METHODS

Four Guardian® REAL-Time CGM systems (CGMSs) (Medtronic Diabetes, Minimed, CA) and eight glucose sensors were tested in glucose solutions prepared in Krebs bicarbonate buffers at 37 °C. Glucose readings obtained from CGMSs were compared with actual glucose concentrations during controlled changes in glucose concentration performed at four rates (30, 90, and 220 mg/dl/hr(-1) and an instantaneous change of 110 mg/dl) using a linear gradient maker.

RESULTS

Irrespective of the rate and direction of changes in glucose concentration, the readings obtained from CGMSs were significantly different from actual glucose levels. The faster the rise or fall in actual glucose concentration, the more pronounced the mismatch with CGMS glucose readings. Furthermore, the intrinsic lag times (8.3 to 40.1 min) were high enough to account for the lags reported in previous in vivo studies.

CONCLUSIONS

The lag intrinsic of the CGMS may make a significant contribution to the mismatch between CGM system readings and blood glucose concentrations.

Continuous glucose monitoring in newborn babies at risk of hypoglycemia

OBJECTIVE

To determine the usefulness of continuous glucose monitoring in babies at risk of neonatal hypoglycemia.

STUDY DESIGN

Babies >/=32 weeks old who were at risk of hypoglycemia and admitted to newborn intensive care received routine treatment, including intermittent blood glucose measurement using the glucose oxidase method, and blinded continuous interstitial glucose monitoring.

RESULTS

Continuous glucose monitoring was well tolerated in 102 infants. There was good agreement between blood and interstitial glucose concentrations (mean difference, 0.0 mmol/L; 95% CI, -1.1-1.1). Low glucose concentrations (<2.6 mmol/L) were detected in 32 babies (32%) with blood sampling and in 45 babies (44%) with continuous monitoring. There were 265 episodes of low interstitial glucose concentrations, 215 (81%) of which were not detected with blood glucose measurement. One hundred seven episodes in 34 babies lasted >30 minutes, 78 (73%) of which were not detected with blood glucose measurement.

CONCLUSION

Continuous interstitial glucose monitoring detects many more episodes of low glucose concentrations than blood glucose measurement. The physiological significance of these previously undetected episodes is unknown.

Frequency of biochemical hypoglycaemia in adults with Type 1 diabetes with and without impaired awareness of hypoglycaemia: no identifiable differences using continuous glucose monitoring

OBJECTIVE

Impaired awareness of hypoglycaemia (IAH) is a major risk factor for severe hypoglycaemia in Type 1 diabetes. Although biochemical hypoglycaemia is asserted to be more frequent in IAH, this has not been estimated accurately. The aim of this study was to use Continuous Glucose Monitoring (CGM) to quantify hypoglycaemia in IAH and evaluate its use in identifying impaired awareness of hypoglycaemia.

METHODS

Ninety-five patients with Type 1 diabetes were classified as having normal (n = 74) or impaired awareness (n = 21) using an established method of assessing hypoglycaemia awareness. Hypoglycaemia exposure was assessed prospectively over 9-12 months using weekly 4-point capillary home blood glucose monitoring (HBGM), 5 days of CGM and prospective reporting of severe hypoglycaemia. The frequencies of biochemical and severe hypoglycaemia were compared in patients with normal and impaired awareness of hypoglycaemia.

RESULTS

Patients with impaired awareness had a 3-fold higher incidence of severe hypoglycaemia than those with normal awareness [incidence rate ratio (IRR) 3.37 (95% CI 1.30-8.7); P = 0.01] and 1.6-fold higher incidence of hypoglycaemia on weekly HBGM [IRR 1.63 (95% CI 1.09-2.44); P = 0.02]. No significant differences were observed with CGM [IRR for sensor glucose < or = 3.0 mmol/l 1.47 (95% CI 0.91-2.39); P = 0.12; IRR for sensor glucose < or = 2.2 mmol/l 1.23 (95% CI 0.76-1.98); P = 0.40].

CONCLUSIONS

Patients with Type 1 diabetes with impaired awareness had a 3-fold higher risk of severe hypoglycaemia and 1.6-fold higher incidence of biochemical hypoglycaemia measured with weekly glucose monitoring compared with normal awareness, but 5 days of CGM did not differentiate those with impaired from those with normal awareness.

Dissolved core alginate microspheres as "smart-tattoo" glucose sensors

The feasibility of multilayer thin film coated dissolved-core alginate-templated microsphere sensors based on fluorescence resonance energy transfer and competitive binding, was explored in simulated interstitial fluid, using glucose as a model analyte. The glucose sensitivity was observed to be 0.89%/mM glucose with a linear response in the range of 0-50 mM glucose. The sensor response was observed to be completely reversible in nature with a response time of 120 seconds. The system was further demonstrated to respond similarly using near-infrared dyes (Alexa Fluor-647-labeled dextran as donor and QSY-21-conjugated apo-GOx as acceptor) which exhibited a sensitivity of 0.94%/mM glucose with a linear response in range of 0-50 mM glucose, making the sensor more amenable to in vivo use, when implanted in scattering tissue.

Motilin concentrations in relation to gastro intestinal dysmotility in diabetes mellitus

AIM

Dysmotility in the upper gastro intestinal (GI) tract are common problems in diabetics. Many peptides are involved in the regulation of the motility. The aim of this study was to examine whether plasma levels of motilin were related to dysfunction in the oesophagus and stomach in a well-defined diabetic patient group.

METHODS

Nineteen patients with symptoms from the GI tract who had been examined with oesophageal manometry, gastric emptying scintigraphy and deep-breathing test were included. They received a fat-rich meal, after which blood samples were collected and analysed for motilin concentrations.

RESULTS

Symptoms of abdominal fullness and gastro oesophageal reflux significantly associated with delayed gastric emptying, whereas no symptom correlated to oesophageal dysmotility. Plasma levels of motilin were increased after the fat-rich meal (p=0.000), with no difference between the groups. Abnormal manometry was characterized by aperistalsis and/or simultaneous contractions. The percentage of simultaneous contractions correlated to basic and peak motilin values (r(s)=0.898, p=0.006 and r(s)=0.842, p=0.017, respectively). Gastric emptying did not influence motilin concentrations.

CONCLUSION

Plasma motilin concentrations vary with abnormalities of oesophageal motility in diabetics, but not with abnormalities of gastric emptying.

Hypoglycaemia: an overview

Hypoglycaemia is a frequent side-effect of treatment with insulin and sulfonylureas for people with diabetes, threatening potentially serious morbidity and preventing optimal glycaemic control. Fear of hypoglycaemia and development of syndromes such as impaired awareness and counterregulatory deficiency provide additional hazards for intensification of treatment. Rapid lowering of HbA1c may be potentially dangerous in type 2 diabetes because of the adverse cardiovascular effects induced by hypoglycaemia. Hypoglycaemia can disrupt many everyday activities such as driving, work performance and recreational pursuits. Measures to reduce the risk of hypoglycaemia are labour-intensive and require substantial resources.

A tale of two compartments: interstitial versus blood glucose monitoring

Self-monitoring of blood glucose was described as one of the most important advancements in diabetes management since the invention of insulin in 1920. Recent advances in glucose sensor technology for measuring interstitial glucose concentrations have challenged the dominance of glucose meters in diabetes management, while raising questions about the relationships between interstitial and blood glucose levels. This article will review the differences between interstitial and blood glucose and some of the challenges in measuring interstitial glucose levels accurately.

Real-time continuous glucose monitoring in the clinical setting: the good, the bad, and the practical

Real-time continuous glucose monitoring (RT-CGM) is the latest technological breakthrough in diabetes care. Despite its limitations of lag time between sensor and blood glucose, the need for calibration, false detection of and failure to detect hypoglycemia, and mild discomfort or skin irritation reported in some users, RT-CGM is a highly beneficial tool that can be used to detect nocturnal or unrecognized hypoglycemia and glycemic variability. This, in turn, can lead to better treatment decisions, which may improve metabolic control and decrease the incidence and progression of diabetes complications. The RT-CGM devices are fairly accurate and easy to use. It is not difficult to establish a clinical RT-CGM program in the office. However, it requires persistence and an understanding of the patient's perspective of using RT-CGM so it can be presented and taught appropriately. This article discusses the benefits and limitations of RT-CGM and establishment of a RT-CGM program in the clinical setting.

The effect of continuous subcutaneous glucose monitoring (CGMS) versus intermittent whole blood finger-stick glucose monitoring (SBGM) on hemoglobin A1c (HBA1c) levels in Type I diabetic patients: a systematic review

BACKGROUND AND PURPOSE

Continuous glucose monitoring (CGMS) is a relatively new technology that measures interstitial glucose every 5 min for 72 h. The resulting profile provides a more comprehensive measure of glycemic excursions than intermittent self-blood finger-stick glucose monitoring (SBGM) and thus could potentially improve diabetes control. We performed a meta-analysis of randomized controlled trials comparing CGMS and SBGM in Type 1 diabetic patients. Our aim was to determine whether CGMS leads to better hemoglobin A1c (HBA1c) levels, a marker of long-term vascular risk.

METHODS

Randomized controlled trials comparing CGMS and SBGM in Type 1 diabetic patients were identified using both manual and electronic searches of the literature in MEDLINE, EMBASE, PUBMED and Cochrane Central Registry of Controlled Trials from 1996 to March 2007. Relevant studies were independently selected by two reviewers, who also extracted data on study design, quality and effect on HBA1c levels. Data from all trials were pooled using a random effects model.

RESULTS

Seven studies with a total of 335 patients fulfilled the inclusion criteria. Five studies were confined to the pediatric population (age<18 years). Study duration varied from 12 to 24 weeks. Compared with SBGM, CGMS was associated with a non-significant reduction in HBA1c (0.22%; 95% CI: -0.439% to 0.004%, p=0.055).

CONCLUSIONS

There is insufficient evidence to support the notion that CGMS provides a superior benefit over SBGM in terms of HBA1c reduction. There was some indication of improved detection of asymptomatic nocturnal hypoglycemia in the CGMS group.

Continuous glucose monitoring in patients with insulinoma

BACKGROUND

Insulinomas are rare neuroendocrine tumours that are usually small and may take time to localize. They cause recurrent life-threatening spontaneous hypoglycaemia. Recurrent hypoglycaemia causes loss of hypoglycaemia awareness, putting the patient at further risk, but this has rarely been described in insulinoma. We describe the utility of continuous glucose monitoring (CGM) in patients with insulinoma.

PATIENTS AND METHODS

Three patients, aged 72 years (patient 1), 37 years (patient 2) and 24 years (patient 3), with suspected insulinoma attended our investigation unit, in a university teaching hospital. Biochemical diagnosis was confirmed by elevated plasma insulin and C-peptide during biochemical hypoglycaemia [plasma glucose < 2.2 mM (40 mg/dl)]. Surgery confirmed histology in all. CGM was used to monitor frequency and time of hypoglycaemia during diagnosis and medical treatment, and after definitive surgical treatment.

RESULTS

All patients had evidence of hypoglycaemia unawareness. At diagnosis in patients 1-3, CGM revealed 6.1%, 21.9% and 71.0% of time spent in moderate hypoglycaemia (plasma glucose 2.2-3.0 mM), and 1.4%, 11.4% and 48.1% of time in severe hypoglycaemia (plasma glucose < 2.2 mM), respectively. On diazoxide this reduced to 0.6%, 5.4% and 5.7% time in moderate hypoglycaemia, and no severe hypoglycaemia in patients 1 and 3, and 0.5% in patient 2. Octreotide therapy in patients 2 and 3 resulted in 5.8% and 0% of time in moderate hypoglycaemia, respectively, and no severe hypoglycaemia. After surgical excision CGM confirmed cure in all.

CONCLUSIONS

CGM in insulinoma is useful in detecting hypoglycaemia, and hypoglycaemia unawareness, monitoring response to medical therapy and for confirming cure postoperatively, and is useful in the management of this uncommon but dangerous condition.

Early elective insulin therapy can reduce hyperglycemia and increase insulin-like growth factor-I levels in very low birth weight infants

OBJECTIVE

To investigate the use of insulin throughout the first week of life in very low birth weight (VLBW) infants (birth weight <1.5 kg) to improve glucose control and increase insulin-like growth factor-I (IGF-I) levels. IGF-I is the dominant hormone involved in fetal growth, and low levels have been implicated in neonatal morbidities, such as retinopathy of prematurity.

STUDY DESIGN

In this pilot randomized controlled study (n = 16), the intervention group received insulin (0.025 U/kg/hr) on days 1 to 7, with 20% dextrose to maintain normoglycemia. Control infants received standard neonatal care. All infants received continuous glucose monitoring.

RESULTS

The intervention and standard care groups had similar mean gestational age (+/- standard deviation), 26.2 (+/- 2.5) vs 26.9 (+/- 2.7) weeks, and birth weight, 0.79 (+/- 0.26) vs 0.73 (+/- 0.16) kg. The standard care infants were hyperglycemic (sensor glucose >10 mmol/L [180 mg/dL]) for 35.9% of the study period, compared with 7.6% for the insulin-treated infants (P = .035). The duration of time with hypoglycemia (<2.6 mmol/L [47 mg/dL]) did not differ between the 2 groups (P = .746). The insulin-treated group had a 2.4-fold increase in mean IGF-I bioactivity (P = .005).

CONCLUSIONS

Early insulin therapy improves blood glucose control and increases IGF-I bioactivity levels. This could result in less morbidity associated with hyperglycemia and reduced IGF-I levels.

Treatment with insulin glargine reduces asymptomatic hypoglycemia detected by continuous subcutaneous glucose monitoring in children and adolescents with type 1 diabetes

OBJECTIVE

Unsatisfactory basal insulin substitution may lead to asymptomatic hypoglycemia in children and adolescents with type 1 diabetes (T1D). To investigate the effects of multiple daily injections before and after changing to insulin glargine (IG), continuous glucose monitoring system (CGMS) data were used to analyze glycemic control and hypoglycemic episodes during the two different therapy regimens.

METHODS

Basal insulin therapy was changed to one daily injection of IG in 30 pediatric patients with T1D (14 boys and 16 girls; age 4.5-18.3 yr, median 14.2 yr; diabetes duration 0.5-15.6 yr, median 4.6 yr) having elevated fasting glucose or recurrent hypoglycemia despite treatment with multiple injection therapy (basal insulin: two to four injections of neutral protamine Hagedorn (NPH) and/or zinc lente insulin). Ambulatory CGMS was applied before and 6-8 wk after treatment change. Frequency of hypoglycemic and hyperglycemic episodes, glucose area under the curve (AUC), and time below 60 mg/dL and above 180 mg/dL, respectively, were calculated from CGMS data during the day (8:00-22:00 hours) and at night (22:00-8:00 hours).

RESULTS

Nocturnal hypoglycemia was detected by CGMS in 20 patients before and in 12 patients after the change to IG (p = .039), whereas both, the number of nocturnal and diurnal hypoglycemic episodes, decreased not significantly from 41 to 36 (p = .758) and 48 to 28 (p = .055), respectively. AUC and time below 60 mg/dL as well as hemoglobin A1c (HbA1c) were not significantly different before and after the change to IG.

CONCLUSION

Under treatment with IG, asymptomatic hypoglycemia was reduced without increase of HbA1c.

Risk of hypoglycaemia in types 1 and 2 diabetes: effects of treatment modalities and their duration

AIMS/HYPOTHESIS

We explored the epidemiology of hypoglycaemia in individuals with insulin-treated diabetes by testing the hypothesis that diabetes type and duration of insulin treatment influence the risk of hypoglycaemia.

MATERIALS AND METHODS

This was an observational study over 9-12 months in six UK secondary care diabetes centres. Altogether 383 patients were involved. Patients were divided into the following three treatment groups for type 2 diabetes: (1) sulfonylureas, (2) insulin for <2 years and (3) insulin for >5 years, and into two treatment groups for type 1 diabetes, namely <5 years disease duration and >15 years disease duration. Self-reported (mild and severe) and biochemical episodes (interstitial glucose <2.2 mmol/l using continuous glucose monitoring) were recorded.

RESULTS

Mild hypoglycaemia in type 2 diabetic patients on insulin for <2 years was less frequent than in type 1 patients with <5 years disease duration (mean rate: 4 vs 36 episodes per subject-year, p < 0.001). In type 2 diabetic patients treated with sulfonylureas or insulin for <2 years, no differences were observed in the proportion experiencing severe hypoglycaemia (7 vs 7%, difference 0 [95% CI: -7 to 9%]), mild symptomatic (39 vs 51%, difference 12 [-3 to 25%]) or interstitial glucose <2.2 mol/l (22 vs 20%, difference 2 [-13 to 10%]). Severe hypoglycaemia rates were comparable in patients with type 2 diabetes on sulfonylureas or insulin < 2 years (0.1 and 0.2 episodes per subject-year) and far less frequent than in type 1 diabetes (<5 years group, 1.1; >15 years group, 3.2.episodes per subject-year).

CONCLUSIONS/INTERPRETATION

During early insulin use in type 2 diabetes, the frequency of hypoglycaemia is generally equivalent to that observed in patients treated with sulfonylureas and considerably lower than during the first 5 years of treatment in type 1 diabetes.

Unrecognised hypoglycaemia in children and adolescents with type 1 diabetes using the continuous glucose monitoring system: prevalence and contributors

AIM

To determine prevalence of hypoglycaemia, and contributing factors, in children with type 1 diabetes, using the Medtronic MiniMed continuous glucose monitoring system (CGMS).

METHODS

Fifty-one children and adolescents with diabetes were studied with the CGMS. The studies were analysed for frequency and duration of hypoglycaemia (below 3.5 and 2.5 mmol/L). Contributing clinical factors were determined. Occurrence of nocturnal hypoglycaemia was related to bedtime and fasting home glucose recording.

RESULTS

Hypoglycaemia was common, with 1 (0-4.2) (median (range)) episode per patient per 24 hours, and 0.33 (0-2) episodes per patient per night. Nocturnal episodes were longer than daytime episodes [97.5 (5-720) versus 35 (5-295) minutes for episodes below 3.5 mmol/L, P < 0.001; and 75 (10-640) versus 25 (5-200) minutes for episodes below 2.5 mmol/L, P < 0.001], and less likely to be recognised by the subject (P < 0.001 for episodes below both 3.5 and 2.5 mmol/L). Nocturnal hypoglycaemia was more common with a bedtime glucose recording <6 mmol/L, but also occurred frequently in subjects with glucose recordings >10 mmol/L. No bedtime glucose value reduced the risk of nocturnal hypoglycaemia to <10%.

CONCLUSION

Hypoglycaemia, assessed using the CGMS, is common in children with type 1 diabetes and can be prolonged (although is predominantly mild). Bedtime home glucose recordings are poorly predictive of hypoglycaemia during the following night. Continuous glucose monitoring has proven very useful in management of individual patients, particularly adolescents experiencing difficulties with adherence to diabetes management.

Oesophageal dysmotility, delayed gastric emptying and autonomic neuropathy correlate to disturbed glucose homeostasis

AIMS/HYPOTHESIS

Among diabetic patients, glucose homeostasis may be affected by abnormal gastrointestinal motility and autonomic neuropathy. This study analysed whether oesophageal dysmotility, delayed gastric emptying or autonomic neuropathy affect glucose homeostasis.

MATERIALS AND METHODS

Oesophageal manometry and gastric emptying scintigraphy were performed in 20 diabetic patients. Heart-rate variation during deep breathing (expiration/inspiration [E/I] ratio) and continuous subcutaneous glucose concentrations for a period of 72 h were also monitored in the same patients.

RESULTS

Oesophageal dysmotility was found in eight of 14 patients. Eleven of 20 patients had delayed gastric emptying (abnormal gastric emptying half-time [T (50)]) and nine of 18 had an abnormal E/I ratio. Complaints of abdominal fullness were predictive of delayed gastric emptying. A low peristaltic speed of the oesophagus was associated with impaired T (50) (r ( s )=-0.67; p=0.02). One hour after breakfast, subcutaneous glucose levels decreased in patients with delayed gastric emptying but continued to rise in those with normal emptying. Consequently, the median glucose level 2.5 h after breakfast was lower in the former (9.1 [4.2-12.5] vs 14.3 [11.2-17.7] mmol/l; p<0.05). Glucose fluctuations during the 72 h were significantly higher in patients with an abnormal E/I ratio than in those with a normal E/I ratio (coefficient of variation: 41 [46-49] vs 28 [27-34]%; p=0.008).

CONCLUSIONS/INTERPRETATION

Abdominal fullness predicted delayed gastric emptying that was associated with diminished glucose uptake after breakfast. Low oesophageal peristaltic speed was associated with slow gastric emptying whereas parasympathetic neuropathy was associated with increased glucose variations.

Biocompatibility of electrochemical glucose sensors implanted in the subcutis of pigs

BACKGROUND

Lowering blood glucose concentration slows or prevents the development of complications in diabetes. One of the tools to control glucose levels is continuous glucose measurements. A promising technique involves measurements from glucose sensors implanted directly in skin/subcutis. However, in vivo bioinstability and drift in sensor signals have been reported after implantation, suggestively caused by the infiltration of inflammatory cells and adhesion of proteins to sensor membranes. The aim of this study was to evaluate the in vivo biocompatibility of two electrochemical glucose sensors after implantation in the skin of pigs.

METHODS

In vivo biocompatibility of in-house fabricated electrochemical glucose sensors and a commercially available continuous glucose monitoring system (CGMS, Medtronic MiniMed, Northridge, CA) implanted 1 h, 2 h, 24 h, 3 days, or 7 days was examined by histological and immunohistochemical techniques.

RESULTS

The extent of inflammation increased significantly as a function of time. The inflammation ranged from an acute focal fibrinous/suppurative dermatitis to a chronic fibrinous and granulating foreign body dermatitis 7 days after implantation. Immunohistochemical stainings showed that heterophilic granulocytes, macrophages, and fibrinogen/fibrinogen fragments D and E were consistent findings. Infiltration of CD3epsilon-positive T-cells was primarily confined to day 7 of implantation. In addition, the pro-inflammatory cytokines interleukin-1 and tumor necrosis factor-alpha played a role in the reaction to sensors.

CONCLUSION

The reported in vivo bioinstability of sensors is likely to be caused by protein and cellular biofouling on the sensor membrane. Furthermore, the consistent finding of fibrinogen and fibrinogen fragments D and E at the sensor-tissue interface seems to play an important role in the pathogenesis as it possibly maintains the inflammation by promoting the recruitment of inflammatory cells to the implantation site.

Continuous subcutaneous glucose monitoring in children with type 1 diabetes mellitus: a single-blind, randomized, controlled trial

BACKGROUND

Tight glycemic control delays the long-term complications of type 1 diabetes mellitus (T1DM) but increases the risk for hypoglycemia. The continuous glucose-monitoring system (CGMS) provides blood glucose (BG) readings every 5 min, and its accuracy and reliability has been established in adults. However, there are limited data on its efficacy and safety in children. The purpose of this study was to determine if CGMS use improves metabolic control in children with T1DM.

METHODS

Twenty-seven children (12 male) with T1DM participated in this single-blind, randomized, controlled trial. Participants (age: 11.4 +/- 3.7 (mean +/- SD) yr, range: 7-17 yr) were randomized to an intervention group (n = 18) or a control group (n = 9). Both groups wore the CGMS for 72-h periods at 0, 2, and 4 months. Adjustments in therapy for the intervention group were based on both CGMS and self-monitoring of BG (SMBG) data, while only SMBG data were used for the control group. Hemoglobin A1c (HbA1c) was determined at 0, 2, 4, and 6 months. The change in HbA1c from 0 to 6 months (HbA1c(Delta1-4)) and mean daily area under the CGMS curve for glucose <70 mg/dL area under the curve (AUC(<70)) were compared between groups.

RESULTS

At study entry, HbA1c levels were similar in the intervention and control groups (8.4 +/- 0.98 and 8.8 +/- 0.86%, respectively; p = 0.12) but were significantly lower in the intervention group compared with the control group at study completion (7.8 +/- 0.88 and 8.6 +/- 0.95%, respectively; p = 0.02). The decrease in HbA1c of 0.61 +/- 0.68% in the intervention group was statistically significant (p = 0.03), whereas the decrease in HbA1c of 0.28 +/- 0.78% in the control group was not. Nonetheless, the differences in HbA1c(Delta1-4) between groups did not reach statistical significance (p = 0.13). There was no statistically significant difference in AUC(<70) between study groups (p = 0.18).

CONCLUSION

CGMS use may improve metabolic control in children with T1DM without increasing the risk for hypoglycemia.

Validation of the Continuous Glucose Monitoring System (CGMS) by the use of two CGMS simultaneously in pregnant women with type 1 diabetes mellitus

BACKGROUND

In pregnant women with type 1 diabetes tight glycemic control reduces perinatal complications. Intensive observation of glucose profiles is essential in the achievement of tight glycemic control. The recent availability of the Continuous Glucose Monitoring System (CGMS, Minimed, Sylmar, CA) creates the opportunity to obtain more complete glucose profiles. This study was aimed at evaluating the accuracy of the CGMS in pregnant women with type 1 diabetes.

METHODS

Five pregnant women with type 1 diabetes were asked to use two CGMS devices simultaneously. The simultaneously measured glucose levels were analyzed using the Pearson correlation, the mean absolute difference, and Bland-Altman analysis. Second, the percentage of concordance of paired data in the hypoglycemic, normoglycemic, or hyperglycemic range was calculated.

RESULTS

The correlation coefficient between simultaneously measured data was 0.94 (P < 0.001). The mean absolute difference was 1.1 +/- 0.8 mmol/L. Bland-Altman analysis shows that 95% of the data pairs have a difference < or = 1.74 mmol/L. Almost 80% of the data pairs could be classified in the same glucose range. In 81% of the non-concordant pairs, one glucose value was classified in the hypoglycemic range and one in the normoglycemic range.

CONCLUSIONS

This study shows that the reproducibility of the CGMS in pregnant women with type 1 diabetes is adequate. This indicates that the CGMS is a useful tool in the management of type 1 diabetes in pregnant women. However, the CGMS should only be used as a supplementary method of daily glucose level measurement as a small degree of error, mainly in the hypoglycemic range, is present.

Interstitial fluid glucose dynamics during insulin-induced hypoglycaemia

AIMS/HYPOTHESIS

Glucose sensors often measure s.c. interstitial fluid (ISF) glucose rather than blood or plasma glucose. Putative differences between plasma and ISF glucose include a protracted delay during the recovery from hypoglycaemia and an increased gradient during hyperinsulinaemia. These have often been investigated using sensor systems that have delays due to signal smoothing, or require long equilibration times. The aim of the present study was to define these relationships during hypoglycaemia in a well-equilibrated system with no smoothing.

METHODS

Hypoglycaemia was induced by i.v. insulin infusion (360 pmol.m(-2).min(-1)) in ten non-diabetic subjects. Glucose was sequentially clamped at approximately 5, 4.2 and 3.1 mmol/l and allowed to return to normoglycaemia. Subjects wore two s.c. glucose sensors (Medtronic MiniMed, Northridge, CA, USA) that had been inserted for more than 12 h. A two-compartment model was used to quantify the delay and gradient.

RESULTS

The delay during the fall in plasma glucose was not different from the delay during recovery (8.3+/-0.67 vs 6.3+/-1.1 min; p=0.27) and no differences were observed in the ratio of sensor current to plasma glucose at basal insulin (2.7+/-0.25 nA.mmol(-1).l) compared with any of the hyperinsulinaemic clamp phases (2.8+/-0.18, 2.7+/-0.021, 2.9+/-0.21; p=NS). The ratio was significantly elevated following recovery to normoglycaemia (3.1+/-0.2 nA.mmol(-1).l; p<0.001).

CONCLUSIONS/INTERPRETATION

The elevated ratio suggests that the plasma to ISF glucose gradient was decreased following hypoglycaemia, possibly due to increased skin blood flow. Recovery from hypoglycaemia is not accompanied by a protracted delay and insulin does not increase the plasma to s.c. ISF glucose gradient.

Can continuous glucose monitoring provide objective documentation of hypoglycemia unawareness?

OBJECTIVE

To establish criteria defining hypoglycemia as detected by the continuous glucose monitoring system (CGMS) in patients with type 1 diabetes that best predict hypoglycemia unawareness (HUN), established by a validated questionnaire.

METHODS

Adult patients were selected for inclusion in this study if they had long-standing type 1 diabetes, a fasting level of C peptide of < or = 0.6 ng/mL, commitment to achieving glycemic control, and a hemoglobin A1c value no higher than 9%. After clinical data and self-monitoring of plasma glucose data were collected, patients underwent a 72-hour glucose monitoring session with use of a Medtronic-MiniMed CGMS. The presence of HUN was determined by a questionnaire. Factors independently associated with HUN were estimated by multivariate independent analysis.

RESULTS

Our study group consisted of 60 patients (33 women and 27 men) who ranged in age from 18 to 84 years (mean, 50.4) and had had diabetes for 5 to 56 years (mean, 23.8). The best predictor of HUN was the maximal duration of hypoglycemia, as determined by the CGMS (P = 0.001). Detection of hypoglycemic episodes with a duration of more than 90 minutes identified patients who had HUN with an 88% specificity and 75% sensitivity. HUN was also significantly associated with use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers (P = 0.003) and with a longer duration of diabetes (P = 0.008).

CONCLUSION

The CGMS can be used for objective detection of patients with HUN.

Reproducibility and reliability of hypoglycaemic episodes recorded with Continuous Glucose Monitoring System (CGMS) in daily life

AIM

Continuous glucose monitoring may reveal episodes of unrecognized hypoglycaemia. We evaluated reproducibility and reliability of hypoglycaemic episodes recorded in daily life by the Medtronic MiniMed Continuous Glucose Monitoring System (CGMS).

METHODS

Twenty-nine adult patients with Type 1 diabetes underwent 6 days of continuous subcutaneous glucose monitoring, applying one CGMS on each side of the abdomen. Blood glucose was measured by HemoCue B-Glucose Analyzers six times daily and two different 4-point calibration sets were generated (set A and B). Using these calibration sets, CGMS raw data were recalibrated generating four different CGMS data sets [left-A (left side of abdomen, calibration set A), left-B, right-A and right-B]. Agreement between CGMS data sets was evaluated during hypoglycaemic events, comparing CGMS readings = 2.2 mmol/l with nadir values from corresponding CGMS data sets. CGMS readings were also compared with independent self-monitored blood glucose (SMBG) values.

RESULTS

With hypoglycaemia (CGMS readings = 2.2 mmol/l) in calibration set left-A, values below 3.5 mmol/l were present in 99% (95% CI: 95-100%) of samples in left-B, 91% (95% CI: 84-96%) of samples in right-A, and 90% (95% CI: 83-95%) of samples in right B. In 84% of these episodes (95% CI: 59-96%) independent SMBG values were below 3.5 mmol/l. Difference in duration was observed with a median difference of 20 min; (left-A vs. right-B).

CONCLUSION

Hypoglycaemic episodes recorded by CGMS are reproducible and agreement with independent SMBG values is acceptable for retrospective recording of hypoglycaemic events with CGMS.

Influence of caffeine on frequency of hypoglycemia detected by continuous interstitial glucose monitoring system in patients with long-standing type 1 diabetes

OBJECTIVE

The aim of this study was to investigate the effect of caffeine (in doses equivalent to normal daily ingestion) on rates and severity of hypoglycemia in patients with long-standing type 1 diabetes to determine the relationship between caffeine, autonomic function, and hypoglycemia.

RESEARCH DESIGN AND METHODS

Using a double-blinded randomized study, we investigated the effect of caffeine versus placebo in 19 patients with long-standing type 1 diabetes using continuous glucose sensing technology and simultaneous assessment of autonomic function using Holter monitoring.

RESULTS

Caffeine reduced the duration of nocturnal hypoglycemia with a mean duration of 49 minutes (range 0-235) versus 132 (0-468) minutes (P = 0.035). The reduction in duration of nighttime hypoglycemia was due to a decline in the number of episodes of moderate hypoglycemia at the expense of mild hypoglycemic episodes (P = 0.04). There was no overall correlation between reduced heart rate variability (a marker of autonomic dysfunction) and hypoglycemic events (r(s) = 0.12, P = 0.62).

CONCLUSIONS

Our results suggest that caffeine is associated with a significant reduction in nocturnal hypoglycemia. The reduction in nocturnal hypoglycemia was not linked to the concomitant rise in parasympathetic activity associated with caffeine.

Evaluation of a continuous glucose monitoring system in cats with diabetes mellitus

A continuous glucose monitoring system (CGMS) was evaluated in 14 cats with naturally occurring diabetes mellitus. The device measures interstitial fluid glucose continuously, by means of a sensor placed in the subcutaneous tissue. All cats tolerated the device well and a trace was obtained on 15/16 occasions. There was good correlation between the CGMS values and blood glucose concentration measured using a glucometer (r=0.932, P<0.01). Limitations to the use of the CGMS are its working glucose range of 2.2-22.2 mmol/l (40-400 mg/dl) and the need for calibration with a blood glucose measurement at least every 12 h. When compared to a traditional blood glucose curve, the CGMS is minimally invasive, reduces the number of venepunctures necessary to assess the kinetics of insulin therapy in a patient and provides a truly continuous glucose curve.