Accuracy & Repeatability

Before I went into social work, I was an electrical engineer and one of the questions that I always asked about meters was, “What is their accuracy and repeatability?” Accuracy is what percentage will the reading vary from the actual reading. If a meter has an accuracy of 10% then if you measure 10 volts, the meter can read between 9 and 11 volts. Repeatability means when you are measuring 10 volts and the meter reads 9.7 volts, it will always read 9.7 volts when you measure 10 volts.

So that leads me to how accuracy and repeatable is my blood glucose meter. I have a One Touch Ultra and I found this report on-line…

Performance Evaluation of a New Blood Glucose Monitor That Requires No Coding: The OneTouch® Vita™ System
Joanna K. Young, B.Sc., John M. Ellison, M.S., and Robert Marshall, Ph.D.

Abstract
Background

Improvements to blood glucose monitoring systems aim to simplify the testing process, reduce or eliminate errors, and provide additional information for patients with diabetes. New systems must continue to demonstrate high-quality analytical performance. The new OneTouch® Vita™ System (LifeScan, Inc., Milpitas, CA) offers a no-code testing process and proven technology found in the OneTouch® Ultra® System. Comparative studies were conducted with the new and established systems to evaluate their precision and accuracy.
[…]
Total Precision

Total precision testing conducted over a 10-day period with control samples also showed similar performance for the two meter systems (Table 2). Coefficients of variation for both systems were well below 5%, with CVs of <3.0% and <3.6% for the OneTouch Vita and OneTouch Ultra Systems respectively.
[…]
Conclusions

Data collected on the new OneTouch Vita System indicate that the meter provides precise and accurate blood glucose readings across a wide range of blood glucose concentrations. Based on standard criteria, the analytical performance of the OneTouch Vita System was found to be comparable to that of the OneTouch Ultra and Ultra2 Systems. By combining no-coding technology with proven test strip design and error detection capabilities, the OneTouch Vita System provides accurate and reliable blood glucose results with greater simplicity of use.

In another study…

Precision and accuracy of two blood glucose meters: FreeStyle Flash versus One Touch Ultra.
Rivers SM, Kane MP, Bakst G, Busch RS, Hamilton RA.
Source

Department of Pharmacy Practice, Albany College of Pharmacy, Albany, NY 12208, USA.
Abstract

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.

And in a third study…

Accuracy of newer-generation home blood glucose meters in a Diabetes Research in Children Network (DirecNet) inpatient exercise study.
Weinzimer SA, Beck RW, Chase HP, Fox LA, Buckingham BA, Tamborlane WV, Kollman C, Coffey J, Xing D, Ruedy KJ; Diabetes Research in Children Network Study Group.
Source

DirecNet Coordinating Center, Jaeb Center for Health Research, Tampa, FL 33647, USA. direcnet@jaeb.org
Abstract
BACKGROUND:

The objective of this study was to assess how the accuracy of the FreeStyle Flash (Abbott Diabetes Care, Alameda, CA) meter compares with that of the One Touch Ultra (Lifescan, Milpitas, CA) home glucose meter (HGM).
RESEARCH DESIGN AND METHODS:

Fifty children with type 1 diabetes (T1D), 10-17 years old, were admitted for two separate 24-h periods to assess the effect of exercise on subsequent nocturnal hypoglycemia. Resulting data were used in a preplanned analysis of the accuracy of the Ultra and FreeStyle HGMs. Glucose levels were measured throughout the day and night and every 15-20 min during a standardized exercise protocol. Reference samples were assayed in a central laboratory using a hexokinase enzymatic method. These reference glucose measurements were paired with HGM values from venous blood obtained within +/- 5 min.
RESULTS:

The median relative absolute difference was 5% for both the Ultra and FreeStyle HGMs, and the percentages of pairs meeting the International Organisation for Standardization criteria were 99% and 98%, respectively. The FreeStyle tended to read slightly higher than the reference method (median difference = +3 mg/dL; P < 0.001), and there was trend in this direction for the Ultra (median difference = +2 mg/dL, P = 0.15). Sensitivities for detection of hypoglycemia (reference < or = 60 and HGM < or = 70 mg/dL) were 96% and 100% for the Ultra and FreeStyle, respectively, and corresponding false-positive rates were both 5%.
CONCLUSIONS:

In a controlled clinical setting using venous blood samples, both the Ultra and FreeStyle meters demonstrated a high degree of accuracy compared with the laboratory reference over a broad range of glucose concentrations in children with T1D.

So what does this all mean? It means that you can probably trust the readings on a One Touch Ultra, that they will be within stated tolerance. The meter is within the stated tolerance of +/- 20 mg/dL and the test accuracy measured were within +/- 15 mg/dL. So if your meter is measuring 100 mg/dL the actual reading could be anywhere from 85 mg/dL to 115 mg/dL. That is a wide range, but the repeatability is less than 3.1%. Therefore, if the meter is reading 100 mg/dL for an actual blood reading of 110 mg/dL, the meter will read between 97 to 100.3 when the actual BG is 110 mg/dL