Effect of ambient temperature on analytical performance of self-monitoring blood glucose systems

Practical considerations for continuous glucose monitoring in elite athletes with type 1 diabetes mellitus: A narrative review

Type 1 diabetes mellitus (T1DM) refers to a metabolic condition where a lack of insulin impairs the usual homeostatic mechanisms to control blood glucose levels. Historically, participation in competitive sport has posed a challenge for those with T1DM, where the dynamic changes in blood glucose during exercise can result in dangerously high (hyperglycaemia) or low blood glucoses (hypoglycaemia) levels. Over the last decade, research and technological development has enhanced the methods of monitoring and managing blood glucose levels, thus reducing the chances of experiencing hyper- or hypoglycaemia during exercise. The introduction of continuous glucose monitoring (CGM) systems means that glucose can be monitored conveniently, without the need for frequent fingerpick glucose checks. CGM devices include a fine sensor inserted under the skin, measuring levels of glucose in the interstitial fluid. Readings can be synchronized to a reader or mobile phone app as often as every 1-5 min. Use of CGM devices is associated with lower HbA1c and a reduction in hypoglycaemic events, promoting overall health and athletic performance. However, there are limitations to CGM, which must be considered when being used by an athlete with T1DM. These limitations can be addressed by individualized education plans, using protective equipment to prevent sensor dislodgement, as well as further research aiming to: (i) account for disparities between CGM and true blood glucose levels during vigorous exercise; (ii) investigate the effects of temperature and altitude on CGM accuracy, and (iii) explore of the sociological impact of CGM use amongst sportspeople without diabetes on those with T1DM.

Evaluation of System Accuracy, Precision, Hematocrit Influence, and User Performance of Two Blood Glucose Monitoring Systems Based on ISO 15197:2013/EN ISO 15197:2015

INTRODUCTION

Sufficiently high analytical quality of blood glucose monitoring systems (BGMS) is a prerequisite for efficient diabetes therapy. In this study we assessed system accuracy, measurement repeatability, intermediate measurement precision, user performance, and the influence of hematocrit on two CE-marked blood glucose monitoring systems. For one BGMS, measurement accuracy using venous samples was additionally investigated.

METHODS

Study procedures were based on the International Organization of Standardization (ISO) 15197:2013/EN ISO 15197:2015 ("ISO 15197"). User performance included data from 100 subjects who used one test strip lot, whereas for all other analyses three different reagent system lots were used. For system accuracy assessment, 100 capillary samples were measured in duplicate with each of three reagent system lots per system, resulting in 600 results per system.

RESULTS

CareSens S Fit and CareSens H Beat both fulfilled the ISO 15197 accuracy criteria with 97.5-100% of each test strip lot's results falling within ± 15 mg/dL or ± 15% of the results of the comparison method and 100% of results in consensus error grid (CEG) zone A for all three lots. User performance evaluation revealed sufficient accuracy in the hands of lay users although some handling errors were documented by study staff. Assessment of measurement repeatability and intermediate measurement precision is given by standard deviation (SD) (glucose levels < 100 mg/dL) and by coefficient of variation (CV) (glucose concentrations ≥ 100 mg/dL). SD was ≤ 4.1 mg/dL and CV ≤ 4.2% for measurement repeatability and SD was ≤ 2.2 mg/dL and CV ≤ 2.6% for intermediate measurement precision. In case of hematocrit influence, both BGMS complied with all three tested lots with the defined criteria.

CONCLUSION

Both BGMS analyzed in this study fulfilled the required accuracy criteria of ISO 15197. They showed high precision, good performance in the hands of lay users, and the influence of hematocrit was acceptable in the labeled range.

External Physical and Technical Influences on Medical Devices for Diabetes Therapy

Home and work situations can expose diabetes medical devices to a number of environmental factors that may influence their function and safety. In accordance with regulatory requirements, manufacturing companies take great care in the construction and design of their products so that environmental factors encountered on a daily basis have as little influence as possible. However, more intense environmental conditions, such as undergoing magnetic resonance imaging (MRI), require patients to remove personal electronic medical devices beforehand. During product development, manufacturers thoroughly investigate how various environmental factors may impact a new medical device. Corresponding operational documents and manufacturer guarantees accompany each device. Similarly, manufacturers investigate any adverse interactions that may occur during communications between medical devices, such as those required with another product, smartphone, or another personal medical device, such as a pacemaker. Questions that arise from patients or medical professionals about a medical device's safety or quality, particularly because of environmental factors, are made to the manufacturer. Manufacturers then often refer to the operating instructions, even though these contain information, such as electromagnetic compatibility, that are difficult to understand for people lacking special technical or physical knowledge. This review highlights the effects of various physical and technical influences on medical devices used in diabetes therapy.

Monitoring of Pediatric Type 1 Diabetes

Regular self-monitoring of blood glucose levels, and ketones when indicated, is an essential component of type 1 diabetes (T1D) management. Although fingerstick blood glucose monitoring has been the standard of care for decades, ongoing rapid technological developments have resulted in increasingly widespread use of continuous glucose monitoring (CGM). This article reviews recommendations for self-monitoring of glucose and ketones in pediatric T1D with particular emphasis on CGM and factors that impact the accuracy and real-world use of this technology.

Wilderness Medical Society Clinical Practice Guidelines for Diabetes Management

The Wilderness Medical Society convened an expert panel in 2018 to develop a set of evidence-based guidelines for the treatment of type 1 and 2 diabetes, as well as the recognition, prevention, and treatment of complications of diabetes in wilderness athletes. We present a review of the classifications, pathophysiology, and evidence-based guidelines for planning and preventive measures, as well as best practice recommendations for both routine and urgent therapeutic management of diabetes and glycemic complications. These recommendations are graded based on the quality of supporting evidence and balance between the benefits and risks or burdens for each recommendation.

Time Lag and Accuracy of Continuous Glucose Monitoring During High Intensity Interval Training in Adults with Type 1 Diabetes

Background: This study investigated the accuracy of real-time continuous glucose monitoring (rtCGM) during high intensity interval training (HIIT) in patients with type 1 diabetes (T1D). Methods: Seventeen participants with T1D, using multiple daily injections (MDI) with basal insulin glargine 300 U/mL (Gla-300), completed four fasted HIIT sessions over 4 weeks while wearing a Dexcom rtCGM G4 Platinum system. Each exercise consisted of high intensity interval cycling and multimodal training over 25 min. Reference venous plasma glucose (PG) was measured at 60- and 10-min before exercise (Stage 1), every 10 min during exercise and then every 15 min until 180 min after the end of exercise (Stage 2: during exercise and 45-min early recovery; Stage 3: 45 min to 3 h after the end of exercise); and at 6-, 10-, and 13-h postexercise (Stage 4). Results: In the 64 HIIT sessions that resulted in hyperglycemia, PG increased 90.0 ± 32.4 mg/dL (mean ± standard deviation), peaking at 68.0 ± 18.4 min from the start of HIIT. Mean absolute relative difference was highest during exercise and early recovery (Stage 2) at 17.8%, versus Stage 1 (10.4%), Stage 3 (10.6%), and Stage 4 (11.5%) (P < 0.001). During Stage 2, rtCGM showed a significant negative bias of 35.3 mg/dL (P < 0.001) compared to reference glucose. Lag time to reach the half-maximal glucose rise was 35 min in rtCGM versus PG. The Surveillance Error Grid found that in Stage 2, only 65.5% of paired values were in the no-risk zone and the %15/15 was 50%, significantly lower than the other stages (P < 0.001). Conclusions: During HIIT and early recovery, there is an increase in lag time and a related decline in accuracy of Dexcom rtCGM G4, compared to pre-exercise and later recovery, in patients with T1D using MDI.

Assessment of System Accuracy, Intermediate Measurement Precision, and Measurement Repeatability of a Blood Glucose Monitoring System Based on ISO 15197

BACKGROUND

Analytical quality of blood glucose monitoring systems (BGMS) is an important aspect for many diabetes patients. Sufficiently high analytical quality is required for adequate diabetes therapy.

METHODS

In this study, system accuracy and measurement precision of a BGMS were assessed based on ISO 15197:2013. For system accuracy, this standard requires a specific glucose distribution and at least 95% of results obtained with the BGMS in capillary blood to fall within ±15 mg/dl or ±15% (at glucose concentrations <100 mg/dl or ≥100 mg/dl, respectively) of corresponding comparison method results, and at least 99% of results to be found within clinically acceptable consensus error grid (CEG) zones A and B. Based on ISO 15197:2013, intermediate measurement precision, using control solution, and measurement repeatability, using venous blood samples, were analyzed by calculation of standard deviations (SDs) and coefficients of variation (CV) at glucose concentrations <100 mg/dl or ≥100 mg/dl, respectively, although ISO 15197:2013 does not specify acceptance criteria.

RESULTS

The BGMS fulfilled system accuracy requirements with ≥99% of results within ±15 mg/dl or ±15% of the comparison method results, and 100% of results in CEG zones A and B. Intermediate measurement precision analysis showed SD ≤2.2 mg/dl and CV ≤2.3%. Analysis of measurement repeatability showed SD ≤2.1 mg/dl and CV ≤2.4%.

CONCLUSION

System accuracy requirements of ISO 15197:2013 were fulfilled by the BGMS. As ISO 15197:2013 does not specify precision requirements, precision analysis results were compared with those reported for other BGMS in the literature and found to be similar.

Accuracy of five systems for self-monitoring of blood glucose in the hands of adult lay-users and professionals applying ISO 15197:2013 accuracy criteria and potential insulin dosing errors

OBJECTIVE

In this study, accuracy in the hands of intended users was evaluated for five self-monitoring of blood glucose (SMBG) systems based on ISO 15197:2013, and possibly related insulin dosing errors were calculated. In addition, accuracy was assessed in the hands of study personnel.

METHODS

For each system (Accu-Chek ¹ Aviva Connect [A], Contour ² Next One [B], FreeStyle Freedom Lite ³ [C], GlucoMen ⁴ areo [D] and OneTouch Verio ⁵ [E]) one test strip lot was evaluated as required by ISO 15197:2013, clause 8. Number and percentage of SMBG measurements within ±15 mg/dl and ±15% of the comparison measurements at glucose concentrations <100 mg/dl and ≥100 mg/dl, respectively, were calculated. In addition, data is presented in surveillance error grids, and insulin dosing errors were modeled. The study was registered at ClinicalTrials.gov (NCT03033849).

RESULTS

Four systems (A, B, C, D) fulfilled the tested reagent system lot ISO 15197:2013 accuracy criteria with the tested reagent system lot with at least 95% (lay-users) and 99.5% (study personnel) of results within the defined limits. Measurements with all five systems were within the clinically acceptable zones of the consensus error grid and the surveillance error grid. Median modeled insulin dosing errors were between -0.8 and +0.6 units for measurements performed by lay-users and between -0.7 and +0.8 units for study personnel. Frequent lay-user errors were not checking the test strips' expiry date, applying blood incorrectly and handling the device incorrectly.

CONCLUSION

In this study, the systems showed slight differences in the number of results within ISO 15197:2013 accuracy limits. Inaccurate SMBG measurements can result in insulin dosing errors and adversely affect glycemic control.

Evaluation of Analytical Performance of Three Blood Glucose Monitoring Systems: System Accuracy, Measurement Repeatability, and Intermediate Measurement Precision

INTRODUCTION

Blood glucose monitoring systems (BGMS) should provide sufficient analytical quality to allow adequate therapy for diabetes patients. Besides system accuracy, measurement precision is an important aspect of a BGMS' analytical quality.

METHODS

Based on ISO 15197:2013/EN ISO 15197:2015, system accuracy, measurement repeatability, and intermediate measurement precision were assessed. ISO 15197:2013 system accuracy criteria require that ⩾95% of individual BGMS' test strip lot results shall fall within ±15 mg/dl or ±15% of corresponding comparison method results (at glucose concentrations <100 mg/dl and ⩾100 mg/dl, respectively), and that ⩾99% of results fall within consensus error grid (CEG) zones A and B. Measurement repeatability was assessed using venous blood samples, whereas intermediate measurement precision was assessed using control solution samples. Standard deviation (SD) and coefficient of variation (CV) were calculated for glucose concentrations <100 mg/dl and ⩾100 mg/dl, respectively. Precision acceptance criteria are not specified by ISO 15197:2013.

RESULTS

All three BGMS fulfilled system accuracy criteria with 96% to 98% of individual test strip lot's results falling within the acceptable accuracy limits. All measurement results fell within CEG zones A and B. For measurement repeatability, SD was ⩽3.3 mg/dl, and CV was ⩽3.9% for the investigated BGMS. Assessment of intermediate measurement precision showed SD ⩽1.3 mg/dl and CV ⩽3.0%.

CONCLUSION

All three BGMS fulfilled system accuracy criteria of ISO 15197:2013. In absence of acceptance criteria, precision results were found to be consistent with the manufacturer's labeling of the investigated devices.

Performance of the Flash Glucose Monitoring System during exercise in youth with Type 1 diabetes

AIM

Metabolic changes during exercise may affect the accuracy of glucose sensors impacting on Type 1 diabetes (T1D) management. The present study aimed at assessing the performance of the Flash Glucose Monitoring system (isCGM) during exercise and in free-living condition in youth with T1D.

METHODS

Seventeen youth (53% male), aged 13.7 ± 3.8 years, with T1D for 5.4 ± 3.8 years, HbA1c 7.4 ± 1.0% (57 ± 11 mmol/mol), were enrolled. Paired isCGM, plasma (PG) and capillary (CG) glucose values (total of 136) were collected during an interval exercise (45 min at 55% VO_2max load with 20 s sprints at 80% VO_2max every 10 min). Paired isCGM and CG (total of 832) were collected during free-living condition.

RESULTS

During exercise, isCGM absolute relative difference (ARDs) means/medians were 12.5/9.4% versus PG and 15.4/10.8% versus CG. During rest, ARDs means/medians were 16.6/12.0%. The Consensus Error Grid analysis showed 98.4% of readings during exercise and 97.24% during rest in zones A + B. Percentage of readings meeting the ISO criteria for CG levels <5.55 mmol/L was 62.5% during exercise, 53.4% during rest; for CG levels ≥5.55 mmol/L was 64.0% during exercise, 60.4% during rest.

CONCLUSIONS

isCGM demonstrated similar clinical safety and performance during exercise and in everyday life; further studies are needed to confirm its accuracy during exercise.

The real world of blood glucose point-of-care testing (POCT) system running in China teaching hospital

BACKGROUND

 The blood glucose point-of-care testing (POCT) system is important in the decision-making process involving patients suspected of having hypoglycemia. To investigate the real world of the POCT system being used in teaching hospitals in China.

METHODS

The survey was conducted by Hisend Research Group from May 2015 to July 2015 in four teaching hospitals in China. The survey questions were referred to the ISO 15197:2013 standard requirements for the use of the POCT system in a hospital setting.

RESULTS

A total of 170 subjects were included from 4 hospitals, which included nursing staff, nurse unit managers, employees from the department of medical instruments, and staff members employed by the clinical laboratories in the Tianjin Metabolism Hospital, Nanjing First Hospital, First Affiliated Hospital of Dalian Medical University, and the First hospital affiliated with the Xi'an Transportation University. The average score for the four hospitals surveyed in this study was 66.6, which varied from 46.1 to 79.7. The main factors influencing the scores were the multiple choices of blood-glucose meters, and the quality control assessment.

CONCLUSION

Our data indicates that the real world use of the POCT system in hospital settings in China needs more closer adherence to a quality management framework.

Seasonal variation in hospital encounters with hypoglycaemia and hyperglycaemia

AIM

To assess whether rates of hospital encounters with hypoglycaemia and hyperglycaemia display seasonal variation.

METHODS

Time series analyses of the monthly rates of hospital encounters (emergency room visits or inpatient admissions) with hypoglycaemia and hyperglycaemia from 2003 to 2012 using linked healthcare databases in Ontario, Canada.

RESULTS

Over the study period, there were 129 887 hypoglycaemia and 79 773 hyperglycaemia encounters. The characteristics of people at the time of their encounters were similar across the seasons in 2008 (median age 68 years for hypoglycaemia encounters and 53 years for hyperglycaemia encounters; 50% female; 90% with diabetes). We observed moderate seasonality in both types of encounters (R² autoregression coefficient 0.58 for hypoglycaemia; 0.59 for hyperglycaemia). The rate of hypoglycaemia encounters appeared to peak between April and June, when on average, there was an additional 49 encounters per month (0.36 encounters per 100 000 persons per month) compared with the other calendar months (5% increase). The rate of hyperglycaemia encounters appeared to peak in January, when on average, there was an additional 69 encounters per month (0.50 encounters per 100 000 persons per month) compared with the other calendar months (11% increase).

CONCLUSIONS

In our region, there is seasonal variation in the rate of hospital encounters with hypoglycaemia and hyperglycaemia. Our findings may help to highlight periods of vulnerability for people, may inform future epidemiological studies and may aid in the appropriate planning of healthcare resources.

Interferences and Limitations in Blood Glucose Self-Testing: An Overview of the Current Knowledge

In general, patients with diabetes performing self-monitoring of blood glucose (SMBG) can strongly rely on the accuracy of measurement results. However, various factors such as application errors, extreme environmental conditions, extreme hematocrit values, or medication interferences may potentially falsify blood glucose readings. Incorrect blood glucose readings may lead to treatment errors, for example, incorrect insulin dosing. Therefore, the diabetes team as well as the patients should be well informed about limitations in blood glucose testing. The aim of this publication is to review the current knowledge on limitations and interferences in blood glucose testing with the perspective of their clinical relevance.

The Effects of Temperature and Relative Humidity on Point-of-Care Glucose Measurements in Hospital Practice in a Tropical Clinical Setting

BACKGROUND

Hospitals in tropical countries experience conditions that exceed manufacturer temperature and humidity limits for point-of-care (POC) glucose reagents. Our goal was to assess the effects of out-of-limits storage temperature, operating temperature, and operating humidity on POC glucose measurement reliability.

METHODS

Quality control measurements were performed monthly using glucose test strips stored under controlled conditions and in inpatient wards under ambient conditions. Glucose test strips were evaluated in groups organized by operating temperatures of 24-25 (group 1), 28-29 (group 2), and 33-34°C (group 3), and relative humidity (RH) of ≤70 (group A), ~80 (group B), and ~90% (group C).

RESULTS

Glucose results for different storage conditions were inconsistent. Measurements at higher operating temperatures had lower values with mean differences of -2.4 (P < .001) and -36.5 (P < .001) mg/dL (28-29 vs 24-25°C), and -3.6 (P < .001) and -37.4 (P < .001) mg/dL (33-34 vs 24-25°C) for low and high control levels, respectively. Measurements at higher RH had lower values with mean differences of -4.0 (P < .001) and -13.2 (P < .001) mg/dL (~80 vs ≤70% RH), and -5.8 (P < .001) and -16.6 (P < .001) mg/dL (~90 vs ≤70% RH) for low and high levels, respectively.

CONCLUSIONS

High temperature and high RH decreased glucose concentrations for the POC oxidase-based system we evaluated. We recommend that individual hospitals perform stress testing, then determine if maximum absolute differences, which represent highest risk for patients, are clinically significant for decision making by using error grid analysis.

A Comparison Study Between Point-of-Care Testing Systems and Central Laboratory for Determining Blood Glucose in Venous Blood

BACKGROUND

Diabetes mellitus is a metabolic disease that is characterized by hyperglycemia. Blood glucose (BG) is helpful for the diagnosis and treatment of diabetes and an important part of the management of diabetes. Point-of-care testing (POCT) is generally used by patients themselves or medical personnel to monitor BG. The objective of this article was to evaluate the accuracy and consistency of POCT on venous blood samples and compare it with the central laboratory system to determine the reliability of POCT measurement results as diagnostic criteria.

METHOD

A total of 162 venous whole blood samples were pooled in this study, which included different concentrations and were determined by three POCT systems randomly. The results were compared with the central laboratory system, which uses the Glucose GOD-PAP method (HITACHI 7600-120). The accuracy was evaluated by the International Organization for Standardization (ISO) 15197:2013.

RESULT

Bland-Altman and Passing-Bablok regression analysis showed three POCT systems that were comparable with the reference method (0.65, 95% CI: -0.57 to 1.86, Y = -0.11 + 0.95X for ACCU-CHEK^® Performa; 0.40, 95% CI: -1.3 to 2.1, Y = 0.036 + 0.96X for ACCU-CHEK^® Active; 0.70, 95% CI: -0.44 to 1.83, Y = -0.073 + 0.95X for OneTouch ^® UltraVue). According to ISO 15197:2013, all POCT systems showed 100% of the results within 0.83 mmol/l (15 mg/dl) at BG concentrations <5.55 mmol/l (100 mg/dl); 92%, 89.2%, and 95.7% of the measurement results within 15% at BG concentrations ≥5.55 mmol/l (100 mg/dl) for ACCU-CHEK^® Performa, ACCU-CHEK^® Active, and OneTouch^® UltraVue, respectively.

CONCLUSIONS

The POCT system cannot replace the central laboratory system as a provider of a standard result in clinical diagnosis. It can only be used as a screening test.

Point-of-care devices for physiological measurements in field conditions. A smorgasbord of instruments and validation procedures

Point-of-care (POC) devices provide quick diagnostic results that increase the efficiency of patient care. Many POC devices are currently available to measure metabolites, blood gases, hormones, disease biomarkers or pathogens in samples as diverse as blood, urine, feces or exhaled breath. This diversity is potentially very useful for the comparative physiologist in field studies if proper validation studies are carried out to justify the accuracy of the devices in non-human species under different conditions. Our review presents an account of physiological parameters that can be monitored with POC devices and surveys the literature for suitable quantitative and statistical procedures for comparing POC measurements with reference "gold standard" procedures. We provide a set of quantitative tools and report on different correlation coefficients (Lin's Concordance Correlation Coefficient or the more widespread Pearson correlation coefficient), describe the graphical assessment of variation using Bland-Altman plots and discuss the difference between Model I and Model II regression procedures. We also report on three validation datasets for lactate, glucose and hemoglobin measurements in birds using the newly proposed procedures. We conclude the review with a haphazard account of future developments in the field, emphasizing the interest in lab-on-a-chip devices to carry out more complex experimental measurements than the ones currently available in POC devices.

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.

Cook and Chill: Effect of Temperature on the Performance of Nonequilibrated Blood Glucose Meters

BACKGROUND

Exposure to extreme temperature can affect the performance of blood glucose monitoring systems. The aim was to determine the non-equilibrated performance of these systems at extreme high and low temperatures that can occur in daily life.

METHODS

The performances of 5 test systems, (1) Abbott FreeStyle Freedom Lite, (2) Roche AccuChek Aviva, (3) Bayer Contour, (4) LifeScan OneTouch Verio, and (5) Sanofi BG Star, were compared after "cooking" (50°C for 1 hour) or "chilling" (-5°C for 1 hour) with room temperature controls (23°C) using whole blood with glucose concentrations of 50, 100, and 200 mg/dl.

RESULTS

The equilibration period (time from the end of incubation to when the test system is operational) was between 1 and 8 minutes, and each test system took between 15 and 30 minutes after incubation to obtain stable measurements at room temperature. Incubating the strips at -5°C or 50°C had little effect on the glucose measurement, whereas incubating the meters introduced bias in performance between 0 and 15 minutes but not subsequently, compared to room temperature controls and at all 3 glucose levels.

CONCLUSIONS

Compensating technologies embedded within blood glucose monitoring systems studied here perform well at extreme temperatures. People with diabetes need to be alerted to this feature to avoid perceptions of malperformance of their devices and the possible inability to get blood glucose readings on short notice (eg, during time of suspected rapid change or before an unplanned meal).

Heat in the Arabian Gulf: An analytical review of the impact of ambient temperature on the oral glucose tolerance test

Diabetes mellitus (DM) and gestational diabetes (GDM) are often diagnosed and their long-term progression monitored either by a fasting blood glucose test (FGT) or an oral blood glucose tolerance test (OGTT). These tests are well-standardized and are conveniently carried out via blood samples drawn from the patient's arm, which are later analyzed to measure blood glucose concentration.

Pre-analytical guidelines for laboratory analysis of blood samples intended for the measurement of plasma glucose maintain that the two principal factors which contribute to poor reproducibility of the OGTT are (i) the variable effects of administration of a hyperosmolar glucose solution on gastric emptying, and (ii) the ambient temperature while the blood sample is being captured. Although viewing ambient temperature as a purely random effect may be acceptable for routine diagnostic tests carried out in “the West”, the substantially higher regular temperatures experienced throughout the year by many African, Asian and Middle-Eastern countries suggest that in some locations and circumstances, ambient temperature might be better regarded as a systematic influence on the OGTT.

The principal purpose of this short literature review is to highlight the potentially significant influence of ambient temperature (during the blood-draw) on the results of OGTT blood glucose measurements. Physicians and healthworkers should be aware of this phenomenon which not only can affect the diagnoses for particular patients but is also capable of producing a significant impact on subsequent prevalence estimates for both diabetes and gestational diabetes. Further studies should be conducted throughout the Arabian Gulf to elucidate the magnitude of this effect on local populations by making use of well-characterized patients under standardized conditions where temperature and humidity can be strictly controlled.

Vulnerability of point-of-care test reagents and instruments to environmental stresses: implications for health professionals and developers

Strategic integration of point-of-care (POC) diagnostic tools during crisis response can accelerate triage and improve management of victims. Timely differential diagnosis is essential wherever care is provided to rule out or rule in disease, expedite life-saving treatment, and improve utilization of limited resources. POC testing needs to be accurate in any environment in which it is used. Devices are exposed to potentially adverse storage and operating conditions, such as high/low temperature and humidity during emergencies and field rescues. Therefore, characterizing environmental conditions allows technology developers, operators, and responders to understand the broad operational requirements of test reagents, instruments, and equipment in order to improve the quality and delivery of care in complex emergencies, disasters, and austere environmental settings. This review aims to describe the effects of environmental stress on POC testing performance and its impact on decision-making, to describe how to study the effects, and to summarize ways to mitigate the effects of environmental stresses through good laboratory practice, development of robust reagents, and novel thermal packaging solutions.

Clinical evaluation of a novel on-strip calibration method for blood glucose measurement

This study evaluated a novel technology for improving accuracy of self-monitoring of blood glucose (SMBG). The technology calibrates each and every test by measuring the response from a predetermined amount of glucose present in the sample chamber of each test strip. SMBG test strips were modified to include a lid coated with a fast dissolving formulation containing glucose. These test strips were characterized for hematocrit (Hct) and temperature induced error response to develop a calibration algorithm. The modified test strips were used in a clinical evaluation involving fingerstick blood samples from 160 subjects. Experiments involving Hct and temperature induced errors show that the technology generates a signal characteristic of the error conditions in any particular test, but independent of glucose concentration, allowing a correction algorithm to be derived. The approach substantially reduced Hct and temperature derived errors. Clinical evaluation using fingerstick blood directly applied to prototype strips showed the error (measured as MARD) was reduced from 11.1 to 5.9% by the on-strip correction approach and the number of outliers reduced by approximately 90%. This technology could improve the accuracy and precision of glucose monitoring systems and so reduce decision errors particularly in clinical situations where hematocrit and temperature may be significant confounders.

Effects of humidity on foil and vial packaging to preserve glucose and lactate test strips for disaster readiness

OBJECTIVE

Efficient emergency and disaster response is challenged by environmental conditions exceeding test reagent storage and operating specifications. We assessed the effectiveness of vial and foil packaging in preserving point-of-care (POC) glucose and lactate test strip performance in humid conditions.

METHODS

Glucose and lactate test strips in both packaging were exposed to mean relative humidity of 97.0 ± 1.1% in an environmental chamber for up to 168 hours. At defined time points, stressed strips were removed and tested in pairs with unstressed strips using whole blood samples spiked to glucose concentrations of 60, 100, and 250 mg/dL (n = 20 paired measurements per level). A Wilcoxon signed rank test was used to compare stressed and unstressed test strip measurements.

RESULTS

Stressed glucose and lactate test strip measurements differed significantly from unstressed strips, and were inconsistent between experimental trials. Median glucose paired difference was as high as 12.5 mg/dL at the high glucose test concentration. Median lactate bias was -0.2 mmol/L. Stressed strips from vial (3) and foil (7) packaging failed to produce results.

CONCLUSIONS

Both packaging designs appeared to protect glucose and lactate test strips for at least 1 week of high humidity stress. Documented strip failures revealed the need for improved manufacturing process.

System accuracy of blood glucose monitoring systems: impact of use by patients and ambient conditions

For self-monitoring of blood glucose by people with diabetes, the reliability of the measured blood glucose values is a prerequisite in order to ensure correct therapeutic decisions. Requirements for system accuracy are defined by the International Organization for Standardization (ISO) in the standard EN ISO 15197:2003. However, even a system with high analytical quality is not a guarantee for accurate and reliable measurement results. Under routine life conditions, blood glucose measurement results are affected by several factors. First, the act of performing measurements as well as the handling of the system may entail numerous possible error sources, such as traces of glucose-containing products on the fingertips, the use of deteriorated test strips, or the incorrect storage of test strips. Second, ambient and sampling conditions such as high altitude, partial pressure of oxygen, ambient temperature, and the use of alternate test sites can have an influence on measurement results. Therefore, the user-friendliness of a system and the quality of the manufacturer's labeling to reduce the risk of handling errors are also important aspects in ensuring reliable and accurate measurement results. In addition, the analytical performance of systems should be less prone to user errors and ambient conditions. Finally, people with diabetes must be aware of the information and instructions in the manufacturer's labeling and must be able to measure and interpret blood glucose results correctly.

Blood‐Glucose Biosensors, Development and Challenges

Diabetes mellitus is one of the major causes of premature illness and death worldwide. The World Health Organization estimated that by 2030, 439 million people, corresponding to 7.8% of the world adult population, will live with diabetes. With an increasing diabetic population, a Blood Glucose Monitoring System (BGMS) is becoming an ever important tool for diabetes management. The history of blood biosensor development can be traced back to 1932, when Warburg and Christian reported the “yellow enzyme” from yeast changed to colorless upon oxidizing its substrate and resumed the yellow color after its oxidation by oxygen. Since then a lot of research and development has taken place on blood glucose sensors, and the biosensor technology has gone through three generations, with the current commercially available BGMS predominantly relies on the second generation of technology. The advantages and challenges of each generation are discussed. This chapter will examine in detail topics covering the areas of electrode substrate and electrode material selection, fluid detection electrode, reaction chamber, chemistry (electrolyte, polymer, enzyme and mediator), detection method, analytical performance, regulatory requirements and the manufacturing process. The chapter will close with the clinical utility and future direction and application of glucose biosensor include a brief introduction to the Continuous Blood Glucose Monitoring System (CGMS).

Assessing the quality of publications evaluating the accuracy of blood glucose monitoring systems

Many studies determine the performance of blood glucose monitoring (BG) systems. Correct evaluation is, however, complex, and apparent contradiction of results creates confusion. This study aimed to provide an overview of frequently made errors and to develop easy-to-use checklists to verify the quality of such studies. Building on the work from Mahoney and Ellison and subsequent re-evaluation, study designs of accuracy studies were assessed, and best practice and internationally accepted norms were determined. Key issues were collated, and two simplified checklists were developed: one for the assessment of analytical accuracy studies and a second for guidance with studies assessing the influence of interferences. The checklists have been used in a feasibility study with 20 representative studies selected from a literature search between 2007 and 2012. This check revealed that limitations in the designs and methods of studies assessing the performance of BG systems are common. The use of the accuracy checklist with the 20 representative studies showed that only 20% were in agreement with most of the issues deemed important and that 40% showed clear nonconcordance with ISO 15197. The use of the interference checklist showed that only 50% of the publications were in good agreement with the quality checks. In agreement with previous studies, which concluded many evaluations are performed poorly and present questionable conclusions, the use of these checklists demonstrated that few publications adhered to international guidelines and recommendations. Taking this into consideration, it becomes obvious that the publications must be examined in more detail to establish their quality and the validity of conclusions drawn.

Accuracy of continuous glucose monitoring during exercise in type 1 diabetes pregnancy

BACKGROUND

Performance of continuous glucose monitors (CGMs) may be lower when glucose levels are changing rapidly, such as occurs during physical activity. Our aim was to evaluate accuracy of a current-generation CGM during moderate-intensity exercise in type 1 diabetes (T1D) pregnancy.

SUBJECTS AND METHODS

As part of a study of 24-h closed-loop insulin delivery in 12 women with T1D (disease duration, 17.6 years; glycosylated hemoglobin, 6.4%) during pregnancy (gestation, 21 weeks), we evaluated the Freestyle Navigator(®) sensor (Abbott Diabetes Care, Alameda, CA) during afternoon (15:00-18:00 h) and morning (09:30-12:30 h) exercise (55 min of brisk walking on a treadmill followed by a 2-h recovery), compared with sedentary conditions (18:00-09:00 h). Plasma (reference) glucose, measured at regular 15-30-min intervals with the YSI Ltd. (Fleet, United Kingdom) model YSI 2300 analyzer, was used to assess CGM performance.

RESULTS

Sensor accuracy, as indicated by the larger relative absolute difference (RAD) between paired sensor and reference glucose values, was lower during exercise compared with rest (median RAD, 11.8% vs. 18.4%; P<0.001). These differences remained significant when correcting for plasma glucose relative rate of change (P<0.001). Analysis by glucose range showed lower accuracy during hypoglycemia for both sedentary (median RAD, 24.4%) and exercise (median RAD, 32.1%) conditions. Using Clarke error grid analysis, 96% of CGM values were clinically safe under resting conditions compared with only 87% during exercise.

CONCLUSIONS

Compared with sedentary conditions, accuracy of the Freestyle Navigator CGM was lower during moderate-intensity exercise in pregnant women with T1D. This difference was particularly marked in hypoglycemia and could not be solely explained by the glucose rate of change associated with physical activity.

Lot-to-lot variability of test strips and accuracy assessment of systems for self-monitoring of blood glucose according to ISO 15197

BACKGROUND

Accurate and reliable blood glucose (BG) measurements require that different test strip lots of the same BG monitoring system provide comparable measurement results. Only a small number of studies addressing this question have been published.

METHODS

In this study, four test strip lots for each of five different BG systems [Accu-Chek® Aviva (system A), FreeStyle Lite® (system B), GlucoCheck XL (system C), Pura™/mylife™ Pura (system D), and OneTouch® Verio™ Pro (system E)] were evaluated with procedures according to DIN EN ISO 15197:2003. The BG system measurement results were compared with the manufacturer's measurement procedure (glucose oxidase or hexokinase method). Relative bias according to Bland and Altman and system accuracy according to ISO 15197 were analyzed. A BG system consists of the BG meter itself and the test strips.

RESULTS

The maximum lot-to-lot difference between any two of the four evaluated test strip lots per BG system was 1.0% for system E, 2.1% for system A, 3.1% for system C, 6.9% for system B, and 13.0% for system D. Only two systems (systems A and B) fulfill the criteria of DIN EN ISO 15197:2003 with each test strip lot.

CONCLUSIONS

Considerable lot-to-lot variability between test strip lots of the same BG system was found. These variations add to other sources of inaccuracy with the specific BG system. Manufacturers should regularly and effectively check the accuracy of their BG meters and test strips even between different test strip lots to minimize risk of false treatment decisions.

Glucose measurement of intensive care unit patient plasma samples using a fixed-wavelength mid-infrared spectroscopy system

OBJECTIVE

Glycemic control is a rapidly developing field in intensive care medicine with the aim of reducing mortality, morbidity, and cost. Current intensive care unit (ICU) glucose measurement technologies are susceptible to interference from medications, volume expanders, and other substances present in critically ill patients. We hypothesized that a fixed-wavelength mid-infrared (mid-IR) spectroscopy system would be accurate for measuring glucose levels of ICU patients.

RESEARCH DESIGN AND METHODS

This is a prospective investigation of plasma samples from two different institutions treating a heterogeneous population of ICU patients. The first 292 samples were collected from 86 patients admitted to Stamford Hospital, and the next 352 samples were collected from 75 patients from three ICUs at the University of Maryland. Plasma samples were measured on a Fourier-transform infrared or a proprietary spectrometer, with a glucose prediction algorithm to correct for spectral interference, which were compared with reference measurements taken using a YSI 2300 glucose analyzer.

RESULTS

Glucose values ranged from 24 to 343 mg/dl. Numerous medications and injury/disease states were observed in the patient populations, with metoprolol, fentanyl, and multiple organ failure the most prevalent. Despite these interferents, there was a high correlation (r ≥ 0.94) and low standard error (≤12.8 mg/dl) between the predicted glucose values and those of the YSI 2300 STAT Plus reference instrument in the three studies. A total of 95.1% of the 644 values in the three studies met International Organization for Standardization 15197 criteria.

CONCLUSION

These results suggest that a fixed-wavelength mid-IR spectrometer can measure glucose accurately in the plasma of ICU patients.