Evaluation of Meal Carbohydrate Counting Errors in Patients with Type 1 Diabetes.

AIM: Correct estimation of meal carbohydrate content is a prerequisite for successful intensified insulin therapy in patients with diabetes. In this survey, the counting error in adult patients with type 1 diabetes was investigated. METHODS: Seventy-four patients with type 1 diabetes estimated the carbohydrate content of 24 standardized test meals. The test meals were categorized into 1 of 3 groups with different carbohydrate content: low, medium, and high. Estimation results were compared with the meals' actual carbohydrate content as determined by calculation based on weighing. A subgroup of the participants estimated the test meals for a second (n=35) and a third time (n=22) with a mean period of 11 months between the estimations. RESULTS: During the first estimation, the carbohydrate content was underestimated by -28% (-50, 0) of the actual carbohydrate content. Particularly meals with high mean carbohydrate content were underestimated by -34% (-56, -13). Median counting error improved significantly when estimations were performed for a second time (p<0.001). CONCLUSIONS: Participants generally underestimated the carbohydrate content of the test meals, especially in meals with higher carbohydrate content. Repetition of estimation resulted in significant improvements in estimation accuracy and is important for the maintenance of correct carbohydrate estimations. The ability to estimate the carbohydrate content of a meal should be checked and trained regularly in patients with diabetes.

Measurement accuracy of two professional-use systems for point-of-care testing of blood glucose.

Background The professional-use systems HemoCue® Glucose 201+ (HC201+) and HemoCue® Glucose 201 RT (HC201RT) are widely used for point-of-care testing (POCT) of blood glucose (BG). HC201RT utilizes unit-use microcuvettes which can be stored at room temperature, whereas HC201+ microcuvettes have to be stored at <8 °C. In this study, system accuracy of HC201+ and HC201RT was evaluated using capillary and venous blood samples. Methods For each system, two reagent system lots were evaluated within a period of 2 years based on testing procedures of ISO 15197:2013, a standard applicable for self-monitoring of blood glucose (SMBG) systems. For each reagent system lot, the investigation was performed by using 100 capillary and 95 to 99 venous blood samples. Comparison measurements were performed with a hexokinase laboratory method. Accuracy criteria of ISO 15197:2013 and POCT12-A3 were applied. In addition, bias was analyzed according to Bland and Altman, and error grid analysis was performed. Results When measuring capillary samples, both systems fulfilled accuracy requirements of ISO 15197:2013 and POCT12-A3 with the investigated reagent system lots. When measuring venous samples, only HC201+ fulfilled these requirements. Bias between HC201+ and reference measurements was more consistent over venous and capillary samples and microcuvette lots than for HC201RT. Error grid analysis showed that clinical actions might have been different depending on which system was used. Conclusions In this study, HC201+ showed a high level of accuracy irrespective of the sample type (capillary or venous). In contrast, HC201RT measurement results were markedly affected by the type of sample.

Proof of Concept Study to Assess the Influence of Oxygen Partial Pressure in Capillary Blood on SMBG Measurements.

BACKGROUND: Measurement results provided by blood glucose monitoring systems (BGMS) can be affected by various influencing factors. For some BGMS using glucose oxidase (GOx)-based test strips, one of these factors is the oxygen partial pressure (pO2) of the applied blood sample. Because assessing the potential influence of pO2 when measuring capillary blood samples is not straight-forward, we performed a proof of concept study. METHOD: Influence of pO2 was investigated for two GOx-based BGMS (BGMS A and B). Measurement results of the GOx-based BGMS were compared with measurement results from a pO2-independent BGMS (BGMS C). A total of 119 samples from 60 subjects were measured, twice with BGMS C, then 6 times each with BGMS A and BGMS B or vice versa, and again twice with BGMS C. Immediately afterward, pO2 was determined. Linear regression analysis based on relative differences between results from BGMS A or BGMS B and results from BGMS C was performed to estimate the degree of pO2 influence. RESULTS: The relative bias between the lowest and highest pO2 values differed by 14.3% for BGMS A, indicating a pO2 influence that might be clinically relevant, and by 9.7% for BGMS B, indicating that pO2 influence may be too small to be reliably detected because of the BGMS' imprecision. CONCLUSIONS: This proof of concept study showed that with the procedures used, a potentially clinically relevant influence of pO2 in capillary blood samples on GOx-based BGMS could be detected. Further larger-scale studies are needed to verify this influence.

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 Four Blood Glucose Monitoring Systems for Self-Testing with Built-in Insulin Dose Advisor Based on ISO 15197:2013: System Accuracy and Hematocrit Influence.

BACKGROUND: Self-monitoring of blood glucose (SMBG) is important in diabetes therapy; however, not all SMBG systems are sufficiently accurate. In addition, some SMBG systems are influenced by the user's hematocrit value. METHODS: System accuracy and hematocrit influence was evaluated for four SMBG systems with built-in insulin dose advisors (Accu-Chek® Aviva Expert [1], FreeStyle InsuLinx [2], FreeStyle Precision Neo [3], MyStar DoseCoach® [4]) based on International Organization for Standardization (ISO) 15197:2013 section 6.3 (system accuracy) and 6.4.3 (packed cell volume [hematocrit]) with three test strip lots for each system. Two different established comparison methods were used to investigate a possible impact of the comparison method on analytical performance data. RESULTS: Two systems (2, 4) fulfilled ISO 15197:2013 accuracy criteria when the manufacturer's comparison measurement method was applied and showed with all three tested lots 97% to 99.5% of results within ±15 mg/dL and ±15% of the comparison measurement results at blood glucose (BG) concentrations <100 and ≥100 mg/dL, respectively, and 100% of results within consensus error grid zones A and B. Regarding hematocrit influences, two systems (3, 4) showed with all three tested lots ≤10 mg/dL and ≤10% difference between the test sample and the respective control sample for BG concentrations <100 and ≥100 mg/dL, respectively, when using the manufacturer's comparison measurement method. CONCLUSIONS: When using the manufacturer's comparison measurement method, two out of four SMBG systems fulfilled the minimum system accuracy requirements of ISO 15197:2013. In addition, varying hematocrit levels can affect measurement results with some SMBG systems with built-in insulin dose advisors.

User Performance Evaluation of Four Blood Glucose Monitoring Systems Applying ISO 15197:2013 Accuracy Criteria and Calculation of Insulin Dosing Errors.

INTRODUCTION: The international standard ISO 15197:2013 requires a user performance evaluation to assess if intended users are able to obtain accurate blood glucose measurement results with a self-monitoring of blood glucose (SMBG) system. In this study, user performance was evaluated for four SMBG systems on the basis of ISO 15197:2013, and possibly related insulin dosing errors were calculated. Additionally, accuracy was assessed in the hands of study personnel. METHODS: Accu-Chek® Performa Connect (A), Contour® plus ONE (B), FreeStyle Optium Neo (C), and OneTouch Select® Plus (D) were evaluated with one test strip lot. After familiarization with the systems, subjects collected a capillary blood sample and performed an SMBG measurement. Study personnel observed the subjects' measurement technique. Then, study personnel performed SMBG measurements and comparison measurements. Number and percentage of SMBG measurements within ± 15 mg/dl and ± 15% of the comparison measurements at glucose concentrations < 100 and ≥ 100 mg/dl, respectively, were calculated. In addition, insulin dosing errors were modelled. RESULTS: In the hands of lay-users three systems fulfilled ISO 15197:2013 accuracy criteria with the investigated test strip lot showing 96% (A), 100% (B), and 98% (C) of results within the defined limits. All systems fulfilled minimum accuracy criteria in the hands of study personnel [99% (A), 100% (B), 99.5% (C), 96% (D)]. Measurements with all four systems were within zones of the consensus error grid and surveillance error grid associated with no or minimal risk. Regarding calculated insulin dosing errors, all 99% ranges were between dosing errors of - 2.7 and + 1.4 units for measurements in the hands of lay-users and between - 2.5 and + 1.4 units for study personnel. Frequent lay-user errors were not checking the test strips' expiry date and applying blood incorrectly. CONCLUSIONS: Data obtained in this study show that not all available SMBG systems complied with ISO 15197:2013 accuracy criteria when measurements were performed by lay-users. TRIAL REGISTRATION: The study was registered at ClinicalTrials.gov (NCT02916576). FUNDING: Ascensia Diabetes Care Deutschland GmbH.

System Accuracy and User Performance Evaluation of an Improved System for Self-Monitoring of Blood Glucose.

An improved test cassette for the integrated Accu-Chek® Mobile system (Roche Diabetes Care GmbH, Mannheim, Germany) has been developed. System accuracy of this improved system was evaluated based on ISO 15197:2013, clause 6.3, for three reagent system lots. According to this standard, at least 95% of the system's measurement results shall be within ±15 mg/dL and ±15% of the results of the comparison method at glucose concentrations <100 mg/dL and ≥100 mg/dL (accuracy criterion A), respectively, and at least 99% of results shall be within consensus error grid zones A and B (accuracy criterion B). In addition, accuracy was evaluated in the hands of users based on ISO 15197:2013, clause 8, with one reagent system lot.