Evaluation of LifeScan One Touch® Glucose Meter Linearity Protocol Using SugarChex Linearity Product.
M.J. Horenzy, J. Roule, M. Govanucci, C. Hanley, M. Burns, V. Warty, and M. Virji (Department of Pathology, Univ. of Pittsburgh School of Medicine, Pittsburgh, PA 15213)
Glucose is the major energy source for the human body and is derived primarily from the dietary carbohydrates. Blood glucose determination is central to the diagnosis and management disorders of carbohydrate metabolism such as diabetes mellitus or hypoglycemia. Because of the importance of timely monitoring, whole blood glucose is increasingly performed at the patient's bedside. We use the LifeScan ONE TOUCH® meter for bedside glucose monitoring. The accuracy of glucose determination is critical to appropriate clinical management of the patient. Operator technique, glucose reagent strip and instrument performance, all have an impact on the accuracy of glucose determination. The method employed to check the accuracy is the LifeScan protocol "Procedure for Laboratory Evaluation of the ONE TOUCH® System using Spiked Blood Samples" (Technical Bulletin 53-327A). The SUGAR-CHEX® Linearity product manufactured by Streck Laboratories, Inc. for use with the ONE TOUCH® glucose meter was tested as a possible alternative to this laborious method. We used four ONE TOUCH® Instruments to compare these linearity procedures. The Johnson and Johnson Ektachem was used as the reference instrument. The combined correlation between the Ektachem and ONE TOUCH® using the LifeScan Procedure yielded a mean r2 of 0.995 and a mean slope of 1.069 with an average intercept of 7.0 using samples spiked with glucose at concentrations between 70- 400 mg/dL (Table 1).. When we compared the SUGAR-CHEX® product with assayed values in the range of 25-483 mg/dL it yielded a mean r2 of 0.998 and a mean slope of 0.988 with a negative intercept of 6.4 (Table 2). The data demonstrated that the SUGAR-CHEX® product performs as well as the ONE TOUCH® Linearity Procedure in determining the accuracy of the ONE TOUCH® glucose meters and is economically a better method.
Introduction
The LifeScan ONE TOUCH II® Hospital Meter, along with the ONE TOUCH® Strips, is used for the quantitative measurement of glucose in whole blood. The whole blood glucose test method employs a dry reagent technology based on the glucose oxidase method and is specific for D-glucose. When a drop of blood is applied to the reagent spot on the ONE TOUCH® strip, glucose oxidase catalyzes the oxidation of glucose resulting in the production of gluconic acid and hydrogen peroxide. The enzyme peroxidase, then catalyzes the reaction of the hydrogen peroxide with chromogens to produce a blue color when oxidized. The intensity of the blue color correlates with the concentration of glucose in the whole blood sample.
In order to determine a "true glucose" it is necessary to verify the linearity of entire glucose monitoring system which includes, operator technique, reagent strip lot variation and instrument performance. Both the LifeScan "Procedure for Laboratory Evaluation of the ONE TOUCH® System using Spiked Blood Samples" and the SUGAR-CHEX® Linearity Procedures were evaluated for this purpose.
Methods and Materials
Four ONE TOUCH® Meters were used for this evaluation. The meters were identified with the numbers of 219, 220, 221 and 222. The ONE TOUCH® Strip lot was 406710A (Code 8). The daily maintenance was completed on these meters and the whole blood glucose analysis was performed in accordance with the LifeScan whole blood glucose procedure using the spiked samples. The same lot of glucose reagent strip was used in testing with the Streck SUGAR-CHEX® product. .In addition, the Johnson and Johnson Ektachem analyzer was used as the reference instrument in this evaluation.
Spiked glucose samples were prepared as described in the LifeScan Bulletin (Number 53-327A prepared 12/89) for use on the ONE TOUCH® Meter. After the samples were spiked, they were mixed well and divided into two aliquots. One aliqout was used to perform the whole blood analysis on the ONE TOUCH® glucose meter. The second aliqout was centrifuged to obtain the plasma which was analyzed on the Ektachem.
The Ektachem glucose values were corrected for 12 percent bias( according to LifeScan protocol) and the ONE TOUCH® Meter values were plotted against these corrected glucose values (Figures 1-4).
SUGAR-CHEX® Linearity (Calibration) Assessment Set specifically made for the ONE TOUCH® Glucose Meter was used in this study. We followed manufacturer's protocol which was provided in the insert to obtain whole blood glucose values.
These glucose values were plotted against the known Glucose Concentrations which were provided in the insert (Figures 5-8).
Results
Table 1: LifeScan Spiking Procedure (Range 70 - 400 mg/dL)
| Meter Number | r Squared | Slope | Intercept |
|---|
| 219 | 0.995 | 1.037 | 2.4 |
| 220 | 0.995 | 1.029 | 1.6 |
| 221 | 0.991 | 1.028 | 6.3 |
| 222 | 0.998 | 1.180 | 17.9 |
| Mean | 0.995 | 1.069 | 7.1 |
| SD | 0.002 | 0.064 | 6.5 |
Table 2: Streck SUGAR-CHEX® Procedure (Range 70 - 400 mg/dL)
| Meter Number | r Squared | Slope | Intercept |
|---|
| 219 | 0.999 | 0.970 | 2.5 |
| 220 | 0.998 | 0.983 | 8.2 |
| 221 | 0.996 | 0.983 | 4.0 |
| 222 | 0.997 | 1.016 | 10.9 |
| Mean | 0.998 | 0.988 | 6.4 |
| SD | 0.017 | 0.017 | 3.3 |
Conclusions
The data indicate that the Streck SUGAR-CHEX® Product performs as well as the LifeScan protocol in determining the accuracy of glucose values obtained using the ONE TOUCH® Glucose Meter System.
Other advantages of using the Streck SUGAR-CHEX product in the Laboratory are as follows:
- Reduced Biohazard risk to the technical staff since there are no blood products required. The SUGAR-CHEX® material is ready to use.
- The SUGAR-CHEX® Product has assayed glucose values. The samples do not have to be analyzed on a reference instrument and a correction factor is applied to compensate for the difference between whole blood and plasma analysis.
- The SUGAR-CHEX® Product is stable for 30 days at room temperature. On the contrary, the spiked samples are not stable due to glycolysis and must be assayed immediately.
- Technical time required to validate meter linearity is reduced. To evaluate the linearity of a single meter using the Streck SUGAR-CHEX® Product one hour is required as compared to four hours with the LifeScan spiking procedure.
- The reagent, technical and consumable materials cost for both the products is comparable.
References
1. Procedure for Laboratory Evaluation of The ONE TOUCH® System using Spiked Blood Samples. Technical Bulletin No. 53-327A, LifeScan Inc., 1989.
2. Assay and Instructional Information SUGAR-CHEX® Linearity Assessment Set for use with ONE TOUCH®. Streck Laboratories Inc., 1994.
3. Kodak Ektachem Clinical Chemistry Slide (GLU), Publication No. MP2-8, Eastman Kodak Company, 1992.
wwwadmin@path.upmc.edu
Who's who -- wwwadmin
