Analytical performance of glucometers used for routine glucose self-monitoring of diabetic patients

A computer aided diagnostic method for the evaluation of type II diabetes mellitus in facial thermograms

Almost 50% of individuals around the globe are unaware of diabetes and its complications. So, an early screening of diabetes is very important at this current situation. To overcome the difficulties such as pain and discomfort to the subjects obtained from the biochemical diagnostic procedures; an infrared thermography is the diagnostic technique which measures the skin surface temperature noninvasively. Thus, the aim of our proposed study was to evaluate the type II diabetes in facial thermograms and to develop a computer aided diagnosis (CAD) system to classify the normal and diabetes. The facial thermograms (n = 160) including male (n = 79) and female (n = 81) were captured using FLIR A 305sc infrared thermal camera. The Haralick textural features were extracted from the facial thermograms based on gray level co-occurrence matrix algorithm. The T_ROI, T_MAX, and T_TOT are the statistical temperature parameters exhibited a significant negative correlation with HbA1c (r = - 0.421, - 0.411, - 0.242, p < 0.01 (T_ROI); r = - 0.259, p < 0.01(T_MAX) and - 0.173, p < 0.05 (T_TOT)). An optimal regression equation has been constructed by using the significant facial variables and standard HbA1c values. The model has achieved sensitivity, specificity, and accuracy rate as 91.42%, 88.57%, and 90% respectively. The anthropometrical variables, extracted textural features and temperature parameters were fed into the classifiers and their performances were compared. The Support Vector Machine outperformed the Linear Discriminant Analysis (84.37%) and k-Nearest Neighbor (81.25%) classifiers with the maximum accuracy rate of 89.37%. The developed CAD system has achieved 89.37% of accuracy rate for the classification of diabetes. Thus, the facial thermography could be used as the basic non-invasive prognostic tool for the evaluation of type II diabetes mellitus.

Twice-Daily vs 4-Times-Daily Glucose Testing in Women With Gestational Diabetes Mellitus: A Pilot Study

OBJECTIVES

In women with gestational diabetes mellitus (GDM), glycemic control is typically assessed by capillary blood glucose (BG) self-monitoring. Currently, the standard method of monitoring is by 4-times-daily self-measurements. The goal of our study was to determine whether twice-daily capillary BG testing is comparable with 4-times-daily testing in women with GDM.

METHODS

Thirty-two women with GDM completed initial dietary counselling and recorded consecutive fasting and 2-h postprandial BG over a 14-day period. We randomly selected 2 of 4 BG measurements on each given day and compared mean (95% confidence interval [CI]) twice-daily vs 4-times-daily BG measurements using paired t tests and Bland-Altman plots. The proportion of 14-day BG measurements above glycemic targets was also compared between twice-daily vs 4-times-daily testing for fasting and postprandial readings.

RESULTS

Comparing twice-daily vs 4-times-daily mean BG, there was a small difference for fasting BG (0.09 mmol/L; 95% CI, 0.03 to 0.14), but not for 2-h postbreakfast (-0.05 mmol/L; 95% CI, -0.17 to 0.06), 2-h postlunch (-0.03 mmol/L; 95% CI, -0.13 to 0.08) or 2-h postdinner (0.05 mmol/L; 95% CI, -0.09 to 0.19) BG. Bland-Altman plots showed general agreement and minimal bias between twice-daily vs 4-times-daily BG, whether fasting or postprandial. There was no significant difference in the proportion of 14-day BG measurements above glycemic targets comparing twice-daily vs 4-times-daily testing in the fasting or postprandial states.

CONCLUSIONS

Twice-daily BG testing appears to generate 14-day average values similar to 4-times-daily BG testing. In women with GDM, whose BG is in target range, twice-daily BG monitoring may reduce inconvenience and cost.

A Review of the Construction of Nano-Hybrids for Electrochemical Biosensing of Glucose

Continuous progress in the domain of nano and material science has led to modulation of the properties of nanomaterials in a controlled and desired fashion. In this sense, nanomaterials, including carbon-based materials, metals and metal oxides, and composite/hybrid materials have attracted extensive interest with regard to the construction of electrochemical biosensors. The modification of a working electrode with a combination of two or three nanomaterials in the form of nano-composite/nano-hybrids has revealed good results with very good reproducibility, stability, and improved sensitivity. This review paper is focused on discussing the possible constructs of nano-hybrids and their subsequent use in the construction of electrochemical glucose biosensors.

Accuracy and precision of four main glucometers used in a Sub-Saharan African Country: a cross-sectional study

Introduction

capillary glucose measurement using point-of-care glucometers is an essential part of diabetes care. We determined the technical accuracy, clinical accuracy and precision of commonly available glucometers against standard spectrophotometry in Cameroon.

Methods

a sample of four glucometers was selected. In the 108 diabetic and non-diabetic participants, blood glucose values obtained by glucometers were compared to the reference laboratory method to determine their technical and clinical accuracies. Precision was determined by repeated measurements using standard solutions of different concentrations.

Results

accu-Chek^® Active, CodeFree™, Mylife™ Pura™ and OneTouch^® Ultra^® 2 values had correlation coefficients of 0.96, 0.87, 0.97 and 0.94 respectively with reference values, and biases of 18.7%, 29.1%, 16.1% and 13.8% respectively. All glucometers had ≥ 95% of values located within the confidence limits except OneTouch^® Ultra^®2. Accu-Chek^® Active, CodeFree™, Mylife™ Pura™ and OneTouch^® Ultra^® 2 had 99%, 93.1%, 100% and 98.0% of values in Parke's zones A and B. The coefficients of variation of the glucometers were all below 5% at all standard concentrations, except for Accu-Chek^® Active for glucose concentrations at100 and 200mg/dL.

Conclusion

no glucometer met all the international recommendations for technical accuracy. Accu-Chek™ Active and Mylife™, Pura™ met the International Organization for Standardization 2013 recommendations for clinical accuracy based on Parke's consensus error grid analysis. All glucometers assessed except Accu-Chek^® Active showed a satisfactory level of precision at all concentrations of standard solutions used.

An electrochemical aptamer-based sensor for the rapid and convenient measurement of L-tryptophan

The field of precision medicine-the possibility to accurately tailor pharmacological treatments to each specific patient-would be significantly advanced by the ability to rapidly, conveniently, and cost-effectively measure biomarkers directly at the point of care. Electrochemical aptamer-based (E-AB) sensors appear a promising approach to this end due to their low cost, ease of use, and good analytical performance in complex clinical samples. Thus motivated, we present here the development of an E-AB sensor for the measurement of the amino acid L-tryptophan, a diagnostic marker indicative of a number of metabolic and mental health disorders, in urine. The sensor employs a previously reported DNA aptamer able to recognize the complex formed between tryptophan and a rhodium-based receptor. We adopted the aptamer to the E-AB sensing platform by truncating it, causing it to undergo a binding-induced conformational change, modifying it with a redox-reporting methylene blue, and attaching it to an interrogating electrode. The resulting sensor is able to measure tryptophan concentrations in the micromolar range in minutes and readily discriminates between its target and other aromatic and non-aromatic amino acids. Using it, we demonstrate the measurement of clinically relevant tryptophan levels in synthetic urine in a process requiring only a single dilution step. The speed and convenience with which this is achieved suggest that the E-AB platform could significantly improve the ease and frequency with which metabolic diseases are monitored. Graphical Abstract.

A novel wireless paper-based potentiometric platform for monitoring glucose in blood

A novel low-cost, compact and sensitive paper-based platform for the accurate monitoring of glucose in biological fluids is presented. Paper-based working and reference electrodes are combined to build a whole potentiometric cell, which also fits a sampling module for simple and fast determination of glucose in a single drop of blood. The working electrode is built using a platinized filter paper coated with a Nafion membrane that entraps the enzyme glucose oxidase; the reference electrode is made by casting a polyvinylbutyral-based membrane onto a conductive paper. The system works by detecting the hydrogen peroxide generated as a result of the enzymatic reaction. Selectivity is achieved due to the permselective behaviour of Nafion, while a significant enhancement of the sensitivity is reached by exploiting the Donnan-coupled formal potential. Under optimum conditions, a sensitivity of -95.9 ± 4.8 mV per decade in the 0.3-3 mM range is obtained. Validation of the measurements has been performed against standard methods in human serum and blood. Final integration with a wireless reader allows for truly in situ measurements with a less than 2 minute procedure including a two-point calibration, washing and measurement. This low-cost analytical device opens up new prospects for rapid diagnostic results in non-laboratory settings.

Non-invasive detection of fasting blood glucose level via electrochemical measurement of saliva

Machine learning techniques such as logistic regression (LR), support vector machine (SVM) and artificial neural network (ANN) were used to detect fasting blood glucose levels (FBGL) in a mixed population of healthy and diseased individuals in an Indian population. The occurrence of elevated FBGL was estimated in a non-invasive manner from the status of an individual’s salivary electrochemical parameters such as pH, redox potential, conductivity and concentration of sodium, potassium and calcium ions. The samples were obtained from 175 randomly selected volunteers comprising half healthy and half diabetic patients. The models were trained using 70 % of the total data, and tested upon the remaining set. For each algorithm, data points were cross-validated by randomly shuffling them three times prior to implementing the model. The performance of the machine learning technique was reported in terms of four statistically significant parameters—accuracy, precision, sensitivity and F1 score. SVM using RBF kernel showed the best performance for classifying high FBGLs with approximately 85 % accuracy, 84 % precision, 85 % sensitivity and 85 % F₁ score. This study has been approved by the ethical committee of All India Institute of Medical Sciences, New Delhi, India with the reference number: IEC/NP-278/01-08-2014, RP-29/2014.

Comparison between capillary glucose measured with a Contour glucometer and plasma glucose in a population survey

Capillary glucose (CG) measured with point-of-care glucometers can provide useful approximation of plasma glucose (PG) in selected circumstances but the validity of measurements has been adequately assessed only for a few glucometers.

We assessed the difference between CG measured with a glucometer (Contour Ascensia, Bayer) and PG measured with a standard laboratory method in participants to a population-based cardiovascular survey in the Seychelles (sample size 1227).

CG correlated well with PG (r=0.94; p<0.001). The overall difference between PG and CG was –0.55 mmol/L for PG <4.0 mmol/L (n=19; 95% CI –0.92; –0.18); 0.14 mmol/L for PG 4.0–4.9 (n=344; 95% CI 0.08–0.20) and increased according to PG up to 1.64 mmol/L for PG >9.0 mmol/L (n=68; 95% CI 1.36; 1.91). The prevalence of diabetes in the study sample was 29% lower with CG than with PG (8.6% vs. 12.1%) but this bias could be corrected by analytical re-calibration.

CG underestimated PG, although the bias was small among persons with low glycemia. This systematic difference may bear little significance when the purpose is to simply monitor blood glucose but has large impact on prevalence estimates at the population level if CG values are not adequately calibrated.

Evaluation of an Electrochemical Point-of-Care Meter for Measuring Glucose Concentration in Blood from Periparturient Dairy Cattle

BACKGROUND

The Precision Xtra(®) meter is a promising low cost electrochemical point-of-care unit for measuring blood glucose concentration ([gluc]) in cattle blood. The meter uses an algorithm that assumes the intra-erythrocyte [gluc] equals the plasma [gluc] on a molal basis, and that the hematocrit is similar in humans and cattle.

OBJECTIVES

The primary objective was to determine the accuracy of the meter for measuring plasma [gluc] in dairy cattle. Secondary objectives were to characterize the influence of hematocrit and sample temperature on the measured value for [gluc].

ANIMALS

A total of 106 periparturient Holstein-Friesian cattle.

METHODS

Blood and plasma samples (1,109) were obtained and Deming regression and Bland-Altman plots were used to determine the accuracy of the meter against the reference method (plasma hexokinase assay). Multivariable regression and linear regression were used to determine the effect of hematocrit and sample temperature on the plasma [gluc] measured by the meter.

RESULTS

Intra-erythrocyte [gluc] was 18% of plasma [gluc] on a molar basis. Sample temperature had a significant linear effect on plasma [gluc] as measured by the meter for 3/5 plasma samples when measured [gluc] > 160 mg/dL.

CONCLUSIONS AND CLINICAL IMPORTANCE

The meter utilizes an algorithm that is optimized for human blood and is inaccurate when applied to bovine blood. Until a cattle-specific algorithm is developed, we recommend using plasma as the analyte instead of blood and calculating plasma [gluc] using the equation: [gluc] = 0.66 × [gluc]p-meter + 15, where [gluc]p-meter is the value reported by the meter. If blood is measured, then we recommend using the equation: [gluc] = 0.90 × [gluc]b-meter + 15.

Impact of sensor and measurement timing errors on model-based insulin sensitivity

A model-based insulin sensitivity parameter (SI) is often used in glucose-insulin system models to define the glycaemic response to insulin. As a parameter identified from clinical data, insulin sensitivity can be affected by blood glucose (BG) sensor error and measurement timing error, which can subsequently impact analyses or glycaemic variability during control. This study assessed the impact of both measurement timing and BG sensor errors on identified values of SI and its hour-to-hour variability within a common type of glucose-insulin system model. Retrospective clinical data were used from 270 patients admitted to the Christchurch Hospital ICU between 2005 and 2007 to identify insulin sensitivity profiles. We developed error models for the Abbott Optium Xceed glucometer and measurement timing from clinical data. The effect of these errors on the re-identified insulin sensitivity was investigated by Monte-Carlo analysis. The results of the study show that timing errors in isolation have little clinically significant impact on identified SI level or variability. The clinical impact of changes to SI level induced by combined sensor and timing errors is likely to be significant during glycaemic control. Identified values of SI were mostly (90th percentile) within 29% of the true value when influenced by both sources of error. However, these effects may be overshadowed by physiological factors arising from the critical condition of the patients or other under-modelled or un-modelled dynamics. Thus, glycaemic control protocols that are designed to work with data from glucometers need to be robust to these errors and not be too aggressive in dosing insulin.

Continuous glucose monitoring in newborn infants: how do errors in calibration measurements affect detected hypoglycemia?

Neonatal hypoglycemia is common and can cause serious brain injury. Continuous glucose monitoring (CGM) could improve hypoglycemia detection, while reducing blood glucose (BG) measurements. Calibration algorithms use BG measurements to convert sensor signals into CGM data. Thus, inaccuracies in calibration BG measurements directly affect CGM values and any metrics calculated from them. The aim was to quantify the effect of timing delays and calibration BG measurement errors on hypoglycemia metrics in newborn infants. Data from 155 babies were used. Two timing and 3 BG meter error models (Abbott Optium Xceed, Roche Accu-Chek Inform II, Nova Statstrip) were created using empirical data. Monte-Carlo methods were employed, and each simulation was run 1000 times. Each set of patient data in each simulation had randomly selected timing and/or measurement error added to BG measurements before CGM data were calibrated. The number of hypoglycemic events, duration of hypoglycemia, and hypoglycemic index were then calculated using the CGM data and compared to baseline values. Timing error alone had little effect on hypoglycemia metrics, but measurement error caused substantial variation. Abbott results underreported the number of hypoglycemic events by up to 8 and Roche overreported by up to 4 where the original number reported was 2. Nova results were closest to baseline. Similar trends were observed in the other hypoglycemia metrics. Errors in blood glucose concentration measurements used for calibration of CGM devices can have a clinically important impact on detection of hypoglycemia. If CGM devices are going to be used for assessing hypoglycemia it is important to understand of the impact of these errors on CGM data.

Prevalence of diabetes and hypertension and association with various risk factors among different Muslim populations of Manipur, India

BACKGROUND

Type 2 Diabetes mellitus (DM) and hypertension (HT) are among the most common non-communicable chronic diseases in developed and developing countries around the world. The study reports the prevalence of DM and HT and its influence from its possible risk factors.

METHODS

Individuals of both sexes (Male-1099, Female-669) belonging to six different populations were randomly selected and screened for diabetes and hypertension following from different districts of Manipur, which is a small hilly state, situated in the north eastern extreme corner of India sharing an international boundary with Myanmar (Burma). "Diabetes mellitus" and "hypertension" were defined by the American Diabetes Association and the Joint National Committee's 7th Report guidelines, respectively.

RESULTS

The overall prevalence of diabetes and hypertension in the entire study population was found to be 16.63% and 18.16% respectively. About 13.8% individuals had shown co-prevalence of Diabetes Mellitus and Hypertension. The association of Diabetes Mellitus with different risk factors such as consumption of alcohol and difference in physical activities were found to be statistically significant. The association of Diabetes Mellitus with different populations and age groups are also statistically significant. The association between Hypertension with different populations and different physical activities were also found to be statistically significant.

Impact of retrospective calibration algorithms on hypoglycemia detection in newborn infants using continuous glucose monitoring

BACKGROUND

Neonatal hypoglycemia is common and may cause serious brain injury. Diagnosis is by blood glucose (BG) measurements, often taken several hours apart. Continuous glucose monitoring (CGM) could improve hypoglycemia detection, while reducing the number of BG measurements. Calibration algorithms convert sensor signals into CGM output. Thus, these algorithms directly affect measures used to quantify hypoglycemia. This study was designed to quantify the effects of recalibration and filtering of CGM data on measures of hypoglycemia (BG <2.6 mmol/L) in neonates.

SUBJECTS AND METHODS

CGM data from 50 infants were recalibrated using an algorithm that explicitly recognized the high-accuracy BG measurements available in this study. CGM data were analyzed as (1) original CGM output, (2) recalibrated CGM output, (3) recalibrated CGM output with postcalibration median filtering, and (4) recalibrated CGM output with precalibration median filtering. Hypoglycemia was classified by number of episodes, duration, severity, and hypoglycemic index.

RESULTS

Recalibration increased the number of hypoglycemic events (from 161 to 193), hypoglycemia duration (from 2.2% to 2.6%), and hypoglycemic index (from 4.9 to 7.1 μmol/L). Median filtering postrecalibration reduced hypoglycemic events from 193 to 131, with little change in duration (from 2.6% to 2.5%) and hypoglycemic index (from 7.1 to 6.9 μmol/L). Median filtering prerecalibration resulted in 146 hypoglycemic events, a total duration of hypoglycemia of 2.6%, and a hypoglycemic index of 6.8 μmol/L.

CONCLUSIONS

Hypoglycemia metrics, especially counting events, are heavily dependent on CGM calibration BG error, and the calibration algorithm. CGM devices tended to read high at lower levels, so when high accuracy calibration measurements are available it may be more appropriate to recalibrate the data.

Evaluation of the analytical performance of the coulometry-based Optium Omega blood glucose meter

BACKGROUND

The goal of diabetes treatment is maintaining near normoglycemia based on self-monitoring of blood glucose (SMBG). In this study, an evaluation of the analytical performance of the coulometry-based Optium Omega™ glucose meter designed for SMBG has been carried out.

METHODS

The assessment of precision and between-lot variability was based on glucose measurements in ethylene-diaminetetraacetic acid venous blood samples. Glucose concentrations measured in 289 fresh capillary blood samples using the Omega glucose meter and the Biosen C_line analyzer were compared.

RESULTS

Within-run imprecision coefficient of variation for the lower and higher glucose concentrations amounted to 5.09 and 2.1%, respectively. The relative lot-dependent differences found for the lower and higher glucose concentrations were equal to 6.8 and 2.6%, respectively. The glucose meter error calculated for various concentration ranges amounted from 2.22 to 4.48%. The glucose meter error met the accuracy criteria recommended by the International Organization for Standardization and the American Diabetes Association. The Passing-Bablok agreement test and error grid analysis with 96% of results in zone A indicated good concordance of results, including glucose concentrations below 100 mg/dl.

CONCLUSIONS

The evaluated Optium Omega glucose meter fits the analytical requirements for its use in blood glucose monitoring in diabetes patients.

Glucose biosensors: an overview of use in clinical practice

Blood glucose monitoring has been established as a valuable tool in the management of diabetes. Since maintaining normal blood glucose levels is recommended, a series of suitable glucose biosensors have been developed. During the last 50 years, glucose biosensor technology including point-of-care devices, continuous glucose monitoring systems and noninvasive glucose monitoring systems has been significantly improved. However, there continues to be several challenges related to the achievement of accurate and reliable glucose monitoring. Further technical improvements in glucose biosensors, standardization of the analytical goals for their performance, and continuously assessing and training lay users are required. This article reviews the brief history, basic principles, analytical performance, and the present status of glucose biosensors in the clinical practice.

Evaluation of a glucose meter in determining the glycemic index of chinese traditional foods

BACKGROUND

The purpose of this study was to evaluate whether the Glucometer Elite((R)) meter (Bayer Diagnostics, Kyoto, Japan) (POG) could be used for determining the glycemic index (GI) values of Chinese traditional foods, compared with the YSI (Yellow Springs, OH) glucose analyzer (YSI).

METHODS

After consumption of either glucose or one of 11 test foods, the 2-h postprandial glucose responses were measured separately by POG and YSI. GI values and incremental area under the blood glucose response curve (IAUC) values were then calculated to make comparisons between POG and YSI.

RESULTS

The mean glucose concentration measured by POG was higher than that measured by YSI (5.54 +/- 0.03 vs. 5.30 +/- 0.03 mmol/L, P < 0.01). The mean IAUC calculated by POG data was also higher than that calculated by YSI data (112.93 +/- 4.04 vs. 106.76 +/- 4.06 mmol.min/L, P < 0.01). However, there were no differences in the mean GI value determined by POG and YSI data for each test food.

CONCLUSIONS

Although the glucose concentrations measured by POG were higher than that measured by YSI glucose analyzer, it seemed to be an appropriate instrument to determine the GI values of Chinese traditional foods. However, this conclusion should be cautiously applied to other kinds of glucose meters.

Pharmacokinetic and pharmacodynamic modeling of a monoclonal antibody antagonist of glucagon receptor in male ob/ob mice

Elevated basal concentrations of glucagon and reduced postprandial glucagon suppression are partly responsible for the increased hepatic glucose production seen in type 2 diabetic patients. Recently, it was demonstrated that an antagonistic human monoclonal antibody (mAb) blocking glucagon receptor (GCGR) has profound glucose-lowering effects in various animal models. To further understand the effects on glucose homeostasis mediated by such an antibody, a pharmacokinetic-pharmacodynamic (PK-PD) study was conducted in a diabetic ob/ob mouse model. Four groups of ob/ob mice were randomized to receive single intraperitoneal administration of placebo, 0.6, 1, or 3 mg/kg of mAb GCGR, a fully human mAb against GCGR. The concentration-time data were used for noncompartmental and compartmental analysis. A semi-mechanistic PK-PD model incorporating the glucose-glucagon inter-regulation and the hypothesized inhibitory effect of mAb GCGR on GCGR signaling pathway via competitive inhibition was included to describe the disposition of glucose and glucagon over time. The pharmacokinetics of mAb GCGR was well characterized by a two-compartment model with parallel linear and nonlinear saturable eliminations. Single injection of mAb GCGR caused a rapid glucose-lowering effect with blood glucose concentrations returning to baseline by 4 to 18 days with increasing dose from 0.6 to 3 mg/kg. Elevation of glucagon concentrations was also observed in a dose-dependent manner. The results illustrated that the feedback relationship between glucose and glucagon in the presence of mAb GCGR could be quantitatively described by the developed model. The model may provide additional understanding in the underlying mechanism of GCGR antagonism by mAb.

Standardized evaluation of nine instruments for self-monitoring of blood glucose

BACKGROUND

Instruments for self-monitoring of blood glucose (SMBG) should undergo a standardized evaluation including a user-test before being marketed. In this study the results from standardized evaluations of nine different SMBG instruments are presented, and the standardized evaluation is discussed.

METHODS

Approximately 80 diabetes patients using three lots of test strips participated in each evaluation. Half of the patients were educated in how to use the meter, and the evaluations were carried out by both medical laboratory technologists (MLTs) and patients. Questionnaires were used to assess the user manual and the user-friendliness of the instrument.

RESULTS

The imprecision obtained by the patients (coefficients of variation [CVs] of 3.2-8.1%) were generally higher compared to that by the MLT (CVs of 2.3-5.9%). Three of the nine instruments did not achieve the quality goal based on the recommendation in the International Organization for Standardization's ISO 15197 guideline in the hands of diabetes patients. The bias from the comparison method ranged from -10.4% to +3.2%. There were significant lot-to-lot variations and hematocrit effects for some of the instruments. Temperature difference between the instruments and the test strip caused deterioration of the quality in one instrument. The user-friendliness was in general acceptable.

CONCLUSIONS

The quality of instruments for SMBG seems to have improved during recent years, although there are still analytical problems. A standardized evaluation protocol is necessary and should be regularly revised taking into account the development of new technology and the needs of the patients.

Screening for type 2 diabetes in primary care using a stepwise protocol: the Diabscreen study

AIM

To evaluate a stepwise protocol in opportunistic screening for type 2 diabetes.

METHODS

From 2000 to 2001, in 11 Dutch general practices (n=49,229) we invited at-risk patients during usual care for a capillary fasting plasma glucose (cFPG1) measurement. If >6.0 mmol/l, a second sample (cFPG2) was taken on another day, followed by a venous sample (vFPG) if cFPG2>6.0 mmol/l and cFPG1 or 2> or =7.0 mmol/l.

RESULTS

Of 3724 at-risk patients invited for a cFPG1, 3335 (90%) returned for the measurement. Ultimately, in 125 (4%) of them a vFPG was measured. In 101 out of 125 patients the vFPG was > or =7.0 mmol/l, giving a positive predictive value of our protocol of 81%.

CONCLUSION

A stepwise screening protocol including two subsequent capillary blood glucose measurements from a portable blood glucose meter is well applicable in screening for type 2 diabetes in primary care.

Assessing the Quality of Glucose Monitor Studies: A Critical Evaluation of Published Reports

Background: In recent years, a large number of studies have been published on the performance of glucose monitors. The quality of these reports is not known.

Methods: We searched the PubMed database for performance evaluations of handheld glucose monitors published from August 2002 to November 2006. Relevant articles were compared to 20 recommendations from the Standards for Reporting Diagnostic Accuracy (STARD) and 18 recommendations from the Clinical and Laboratory Standards Institute (CLSI).

Results: A total of 52 reports met our inclusion criteria and were reviewed. None (0%) of the reports conformed to all 38 STARD and CLSI recommendations. The range of compliance to these recommendations varied widely (median 53%; range 21%–84%). Only 1 study of the 52 reported following a CLSI recommendation for checking reference test results. Fewer than half (42%) of the reports contained STARD-recommended statements regarding how and when comparative measurements were performed.

Conclusions: None of the glucose monitor reports from our review conformed to all STARD and CLSI recommendations. Our finding that the average rate of compliance to recommendations was low suggests that many of the researchers did not follow published recommendations for study design, methodology, and reporting and that study quality and conclusions may have been affected. Future studies evaluating the performance of glucose monitoring systems should be carefully designed and follow published recommendations for methodological and reporting quality.

Glucose sensing using near-infrared surface-enhanced Raman spectroscopy: gold surfaces, 10-day stability, and improved accuracy

This research presents the achievement of significant milestones toward the development of a minimally invasive, continuously monitoring, glucose-sensing platform based on the optical quantitation of glucose in interstitial fluid. We expand our initial successes in the measurement of glucose by surface-enhanced Raman scattering (SERS), demonstrating substantial improvements not only in the quality and optical properties of the substrate system itself but also in the robustness of the measurement methodology and the amenability of the technique to compact, diode laser-based instrumentation. Herein, we compare the long-term stability of gold to silver film over nanosphere (AuFON, AgFON) substrates functionalized with a partitioning self-assembled monolayer (SAM) using both electrochemical and SERS measurements. AuFONs were found to be stable for a period of at least 11 days. The switch to AuFONs not only provides a more stable surface for SAM formation but also yields better chemometric results, with improved calibration and validation over a range of 0.5-44 mM (10-800 mg/dL). Measured values for glucose concentrations in phosphate-buffered saline (pH approximately 7.4) based on 160 independent SERS measurements on AuFONs have a root-mean-square error of prediction of 2.7 mM (49.5 mg/dL), with 91% of the values falling within an extended A-B range on an expanded Clarke error grid. Furthermore, AuFONs exhibit surface plasmon resonances at longer wavelengths than similar AgFONs, which make them more efficient for SERS at near-infrared wavelengths, enabling the use of low-power diode lasers in future devices.

Quality control of self-monitoring of blood glucose: why and how?

The control of analytical quality of self-monitoring of blood glucose (SMBG) is recommended as a routine procedure in diabetes management. This control procedure should be easily accessible to patients, convenient, not time-consuming, and provide a reliable assessment of glucose meter performance. Optimally it should be located in the diabetes outpatient clinic. Presently there are two approaches to carrying out SMBG quality control. The first is based on the comparison of results obtained by a controlled glucose meter and use of the laboratory method or point-of-care testing device as a surrogate reference analyzer. The second one is a traditionally organized external quality assessment scheme with use of a dedicated control material, which is distributed to all participants. The recommended allowable meter error in SMBG can be realistically set at 10%.

In Vivo Glucose Measurement by Surface-Enhanced Raman Spectroscopy

This paper presents the first in vivo application of surface-enhanced Raman scattering (SERS). SERS was used to obtain quantitative in vivo glucose measurements from an animal model. Silver film over nanosphere surfaces were functionalized with a two-component self-assembled monolayer, and subcutaneously implanted in a Sprague-Dawley rat such that the glucose concentration of the interstitial fluid could be measured by spectroscopically addressing the sensor through an optical window. The sensor had relatively low error (RMSEC = 7.46 mg/dL (0.41 mM) and RMSEP = 53.42 mg/dL (2.97 mM).

Soluble Aldose Sugar Dehydrogenase from Escherichia coli

A water-soluble aldose sugar dehydrogenase (Asd) has been purified for the first time from Escherichia coli. The enzyme is able to act upon a broad range of aldose sugars, encompassing hexoses, pentoses, disaccharides, and trisaccharides, and is able to oxidize glucose to gluconolactone with subsequent hydrolysis to gluconic acid. The enzyme shows the ability to bind pyrroloquinoline quinone (PQQ) in the presence of Ca2+ in a manner that is proportional to its catalytic activity. The x-ray structure has been determined in the apo-form and as the PQQ-bound active holoenzyme. The beta-propeller fold of this protein is conserved between E. coli Asd and Acinetobacter calcoaceticus soluble glucose dehydrogenase (sGdh), with major structural differences lying in loop and surface-exposed regions. Many of the residues involved in binding the cofactor are conserved between the two enzymes, but significant differences exist in residues likely to contact substrates. PQQ is bound in a large cleft in the protein surface and is uniquely solvent-accessible compared with other PQQ enzymes. The exposed and charged nature of the active site and the activity profile of this enzyme indicate possible factors that underlie a low affinity for glucose but generic broad substrate specificity for aldose sugars. These structural and catalytic properties of the enzymes have led us to propose that E. coli Asd provides a prototype structure for a new subgroup of PQQ-dependent soluble dehydrogenases that is distinct from the A. calcoaceticus sGdh subgroup.

Precision and accuracy of two blood glucose meters: FreeStyle Flash versus One Touch Ultra

PURPOSE

The precision and accuracy of two blood glucose meters were evaluated using finger and forearm blood samples.

METHODS

Duplicate blood glucose measurements on the same forearm and finger as venipuncture were performed with the FreeStyle Flash and the One Touch Ultra. Accuracy was assessed by error-grid analysis and the number of values within 10% of the laboratory reference value. Precision was determined by calculating the absolute mean percent differences in glucose values between the first and second fingers and forearm test results. Forearm testing success was defined as an accurate glucose reading obtained with one lance.

RESULTS

A total of 100 patients completed the study; 93% had diabetes and 53% were female. Patients' mean +/- S.D. age was 63 +/- 12 years, and glucose measurements ranged from 69 to 354 mg/dL. All finger-stick samples fell within error-grid zones A and B; 72% and 57% of FreeStyle Flash and One Touch Ultra values fell within 10% of the laboratory reference values, respectively (p = 0.027). Forearm samples were successfully obtained in 99 and 74 patients using the FreeStyle Flash and One Touch Ultra (p < 0.001), with 64 and 36 samples, respectively, falling within 10% of the laboratory reference values (p = 0.035). There was no difference in meter precision.

CONCLUSION

The FreeStyle Flash and the One Touch Ultra are precise glucose meters; however, the FreeStyle Flash was associated with greater accuracy. Success rates of forearm glucose sampling were significantly greater when the FreeStyle Flash meter was used.

A comparison of blood glucose meters in Australia

OBJECTIVE

To assess the accuracy and precision of the five currently available blood glucose meters in Australia.

DESIGN AND SETTING

Control solutions from manufacturers were used to determine the precision for each meter. Glucose levels in capillary blood samples from 49 patients attending a diabetes clinic were measured with each meter and with a laboratory reference method.

OUTCOME MEASURES

The coefficient of variation was calculated to determine precision. Bias, Error Grid analysis, and Bland-Altman plots were used to determine accuracy.

RESULTS

The CVs of most meters were acceptable at <5%. Bias ranged from 4.0 to 15.5% with only 1 meter satisfying the American Diabetes Association recommendation of <5% bias. Error Grid analysis showed that 94-100% of readings were clinically accurate, and that none of the differences from the reference method would lead to clinical errors. Bland-Altman plots showed that for two meters the magnitude of the difference between the meter and the reference method increased with increasing glucose values, but did not change significantly with glucose level for the other 3 meters.

CONCLUSIONS

Currently available blood glucose meters show acceptable precision, and any errors (with respect to a laboratory method) are highly unlikely to lead to clinical errors. However, only the CareSens meter achieved a bias of less than 5%.

Measurement of glucose and metabolites in subcutaneous adipose tissue during hyperglycemia with microdialysis at various perfusion flow rates

BACKGROUND

Microdialysis-based glucose sensors have recently been introduced for monitoring glucose levels in diabetic patients. The flow rate by which the fluid sample is pumped through the microdialysis catheter varies in different studies.

AIM

To study the effects of various flow rates on glucose and its metabolites sampled by microdialysis during an oral glucose tolerance test.

MATERIAL, METHODS

Glucose, lactate, pyruvate and glycerol were measured with microdialysis in interstitial fluid of subcutaneous adipose tissue in twelve healthy young subjects before and during an oral glucose tolerance test using four different flow rates (0.3, 1, 2 and 5 microL/min) and a 30 mm dialysis membrane.

RESULTS

At the basal fasting state the dialysate glucose obtained by 0.3 microL/min was equal to capillary glucose concentration. A decrease in dialysate glucose levels during the basal state was observed for higher flow rates but not for 0.3 microL/min, which indicates a depleting effect. The relative increase after OGTT was similar for capillary glucose and flow rate 0.3 microL/min but not for higher flow rates.

CONCLUSION

The low microdialysis flow rate (0.3 microL/min) facilitates the capture of true interstitial glucose concentrations during glucose fluctuations. Thus this low flow rate is preferred in studies of local tissue metabolism.

Quality control of SMBG in clinical practice

We present results of quality control of self-monitored blood glucose (SMBG) performed in diabetes outpatient clinic. The tests included: inspection of glucose meter, blood glucose self-measurement by a patient, glucose measurement by point-of-care analyzer used in a clinic and with the laboratory method. In the study 158 glucose meters were controlled and compared with HemoCue glucose analyzer used in the clinic as the reference. 122 glucose meters readings were also compared with the reference laboratory method. Tested glucose meters included: Accutrend {18}, Glucotrend {59}, Precision QiD {39}, One Touch {26} and Glucocard II {16}. Reference glucose assays were performed using glucose oxidase method on Hitachi 911 analyzer. Glucose concentrations measured by the controlled glucose meters ranged from 36 to 425 mg/dL. The analytical bias of the glucose meters amounted from 2.48% to 8.27%. Correlation coefficient between results obtained by the tested glucose meters and HemoCue analyzer ranged from 0.957 to 0.980 and between glucose meters and laboratory method from 0.955 to 0.985. Passing-Bablok agreement test and Deming regression analysis indicated good concordance of results between all the tested glucose meters and HemoCue analyzer, whereas good agreement with the laboratory method was found for Accutrend, Glucotrend, Precision QiD and One Touch glucose meters. In conclusion, good analytical performance of the employed glucose meters and a bias less than 10% from the reference values were found. Results of this study show the possibility for routine, convenient for the patient quality control of SMBG in an outpatient clinic.

Beta cell function and response to treatment in Nigerians with Type 2 diabetes mellitus

There are scant data from African populations on the association between beta-cell function and response to treatment with oral hypoglycaemic agents in Type 2 diabetes mellitus (T2DM). Fasting plasma C-peptide (FCP) and glucagon-stimulated C-peptide (GSCP) levels were measured in 116 Nigerians with T2DM at a university teaching hospital. After 9 months of follow-up and treatment, they were categorized into three groups based on response to treatment: (A) good control but not on maximum sulphonylurea (SU) therapy, (B) inadequate control but not on maximum SU therapy and (C) on maximum SU therapy+/-insulin or biguanide. Logistic regression models were used to investigate how well C-peptide levels predicted the subjects belonging to Group C who are likely to require insulin. The mean FCP and mean GSCP levels of Group C were significantly lower than in the other groups (p=0.024; p= <0.001 respectively). A GSCP cut-off value of < or =1.3 ng/mL predicted membership of Group C with 85% sensitivity and 89% specificity while a cut-off of < or =1.8 ng/mL was associated with 91% sensitivity and 66% specificity. In resource-poor settings where inadequate treatment are common, estimation of GSCP may be useful in predicting treatment response and should be weighed against the cost of inadequate therapy with higher morbidity and mortality.

Comparison of the accuracy of the HemoCue glucose analyzer with the Yellow Springs Instrument glucose oxidase analyzer, particularly in hypoglycemia

OBJECTIVE

We aimed to assess the accuracy of the HemoCue Beta-glucose analyzer (HemoCue) and its correlation with the Yellow Springs Instrument (YSI 2300 STAT; YSI) glucose oxidase analyzer, in particular for hypoglycemic values.

DESIGN AND METHODS

Samples were taken from 24 volunteers during hyperinsulinemic glucose clamp studies. Glucose concentrations were determined immediately with the HemoCue in whole blood and with the YSI in plasma from the same sample. After correction for the difference between whole blood and plasma, the paired plasma glucose concentrations were analyzed with various statistical methods.

RESULTS

A total of 500 paired glucose values were obtained, 209 of which were in the hypoglycemic range. Mean+/-s.e. values were 4.85+/-0.004 mmol/l for the HemoCue (range 1.87-16.17) and 4.81+/-0.004 mmol/l for the YSI (range 1.88-15.00; P = 0.80). In the hypoglycemic region, values were 3.26+/-0.004 mmol/l for the HemoCue (range 1.87-5.17) and 3.22+/-0.003 mmol/l for the YSI (range 1.88-4.20; P = 0.59). Regression analyses were HemoCue = 1.019(YSI) -0.0577 mmol/l, with r = 0.9787 for all values; for hypoglycemic values the HemoCue = 1.1169(YSI) -0.3393 mmol/l, with r = 0.8798. Using Altman's residual plot, the difference was 0.03+/-0.0009 mmol/l, with 18 (3.6%) paired values outside the 95% limits of agreement (-0.82 to 0.89 mmol/l). In the hypoglycemic range, the difference was 0.04+/-0.001 mmol/l, with six (2.9%) values outside the 95% limits of agreement (-0.71 to 0.79 mmol/l). In error grid analysis, one value was in zone D (0.2%) and five values (1%) were in zone B; 98.8% were within zone A.

CONCLUSIONS

Determination of glucose with the HemoCue system had very good correlation with the YSI system in a broad range of glycemia and also for hypoglycemic values. We believe that these methods can be used interchangeably for research and clinical purposes in adults.

Evaluation of a glucose meter for determining the glycemic responses of foods

BACKGROUND

Glucose meters are convenient for measuring postprandial glycemic responses. However, their performance for this purpose has not been evaluated.

METHODS

Glucose responses of 7 potato meals were measured using the One Touch Ultra(R) (OTU) glucose meter and a reference method (Yellow Springs Instruments Glucose Analyzer, YSI) and the incremental areas under the curves (AUC) and glycemic index (GI) values compared.

RESULTS

Mean AUC(OTU) was greater than AUC(YSI) (192+/-8 vs. 175+/-7 mmolxmin/l, p=0.001), but GI(OTU) tended to be less than GI(YSI) (69+/-3 vs. 74+/-3, p=0.052). Bland-Altman difference plots showed wide 95% limits of agreement for AUC (-84 to 119 mmolxmin/l) and GI (-21 to 26) values of individual subjects, and for the mean GI values of the 7 foods (-11 to 21). Total and error variance of AUC and GI values were greater for OTU than YSI, and food means differed significantly for YSI (p<0.01) but not OTU (p=0.11).

CONCLUSION

AUC and GI values determined by OTU are more variable and do not agree well with those obtained by YSI. Thus, the OTU is not recommended for determining AUC or GI in normal subjects. This conclusion does not necessarily apply to other glucose meters whose performance should be evaluated.

Accuracy of the modified Continuous Glucose Monitoring System (CGMS) sensor in an outpatient setting: results from a diabetes research in children network (DirecNet) study

OBJECTIVE

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.

RESEARCH DESIGN AND METHODS

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.

RESULTS

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.

CONCLUSIONS

These data confirm the improved accuracy previously reported for the modified version of the CGMS sensor.

The measurement of alkaline phosphatase at nanomolar concentration within 70 s using a disposable microelectrochemical transistor

We report a new approach to the measurement of alkaline phosphatase concentration based on the use of a disposable poly(aniline) microelectrochemical transistor. The measurement is carried out in a two cell configuration in which the poly(aniline) microelectrochemical transistor operates in acid solution and is connected to the alkaline buffer solution containing the analyte by a salt bridge. Disposable microelectrochemical transistors were reproducibly fabricated by electrochemical deposition of poly(aniline) onto photolithographically fabricated gold microband arrays. Using these devices alkaline phosphatase was detected by employing p-aminophenyl phosphate as the substrate for the enzyme and using glucose and glucose oxidase to recycle the p-aminophenol generated upon enzyme catalysed hydrolysis of the phosphate. Recycling the p-aminophenol with glucose and glucose oxidase amplified the detection of alkaline phosphatase approximately tenfold. Using this approach we obtain linear calibration curves for alkaline phosphatase up to 5 nM within 70 s on single use devices.

Validation of capillary glucose measurements to detect glucose intolerance or type 2 diabetes mellitus in the general population

BACKGROUND

The use of an oral glucose tolerance test (OGTT) has been recommended to diagnose type 2 diabetes, but an OGTT with venous blood sampling may not be feasible in the screening phase preceding large epidemiological studies. We have conducted a population-based screening in 2715 men and women and evaluated the diagnostic validity of capillary plasma glucose concentration measurements versus venous plasma glucose concentration measurements in a subset of 350 subjects.

METHODS

During a single OGTT, glucose concentrations were measured in venous plasma as well as in capillary plasma.

RESULTS

Based on the 1999 WHO criteria for venous glucose concentrations, the study population (n=350) yielded 97 subjects with type 2 diabetes mellitus, 77 subjects with impaired glucose tolerance and 176 subjects with normal glucose tolerance. Sensitivity and specificity to diagnose type 2 diabetes mellitus by capillary plasma were 84% and 98%, respectively. Consistent classification by either venous or capillary plasma glucose measurements was 78% (kappa=0.65, p<0.001).

CONCLUSION

Capillary glucose measurements are suitable for use in epidemiological studies to diagnose and detect type 2 diabetes and normal glucose tolerance. Use of capillary measurements can result in cost-effective inclusion schemes in epidemiological studies.

Indirect sensing of insulin-induced hypoglycaemia by the carotid body in the rat

The most physiologically important sensors for systemic glucoregulation are located in extra-cranial sites. Recent evidence suggests that the carotid body may be one such site. We assessed rat carotid body afferent neural output in response to lowered glucose, indirectly by measurement of ventilation, and directly by recording single or few-fibre chemoafferent discharge, in vitro. Insulin (0.4 Ukg(-1)min(-1))-induced hypoglycaemia (blood glucose reduced by ca 50% to 3.4 +/- 0.1 mmoll(-1)) significantly increased spontaneous ventilation in sham-operated animals but not in bilateral carotid sinus nerve sectioned (CSNX) animals. In both groups, metabolic rate (measured as ) was almost doubled during hypoglycaemia. The ventilatory equivalent was unchanged in the sham group leading to a maintained control level of P(a, CO(2)), but was significantly reduced in the CSNX group, giving rise to an elevation of 6.0 +/- 1.3 mmHg in P(a, CO(2)). When pulmonary ventilation in sham animals was controlled and maintained, phrenic neural activity increased during hypoglycaemia and was associated with a significant increase in P(a, CO(2)) of 5.1 +/- 0.5 mmHg. Baseline chemoreceptor discharge frequency, recorded in vitro, was not affected, and did not increase when the superfusate [glucose] was lowered from 10 mm to 2 mm by substitution with sucrose: 0.40 +/- 0.20 Hz to 0.27 +/- 0.15 Hz, respectively (P > 0.20). We suggest therefore that any potential role of the carotid bodies in glucose homeostasis in vivo is mediated through its transduction of some other metabolically derived blood-borne factor rather than glucose per se and that this may also provide the link between exercise, metabolic rate and ventilation.