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Summary of Slide Presentation No:287
"Alternate
Site Monitoring of Blood Cholesterol"
by Superko, R., Berra, K. and Rudd, C.*
The AccuMeter(R) Cholesterol Test (AccuTech, LLC, Vista, CA) is a single-use, non-instrumented, quantitative test device with accuracy and precision comparable to state-of-the-art, instrumented laboratory methods. The test requires approximately 40ul of fingerstick blood, a two-minute waiting period to allow for filtration, and a simple pulling action of a plastic component within the device. Reliable results are then available in approximately fifteen minutes.
The device is a hand-held cassette comprised of three plastic parts: a cover, a moveable tab, and a base. The cover houses the measurement scale, the blood application well, and two windows through which a color change is noted to signal that the reagents are functioning properly, and that the assay has reached completion. The moveable tab and base operate in synergy to facilitate a sequence of actions and chemical reactions within a series of paper strips. In brief, plasma from the blood sample comes in contact with a buffered protein solution containing horseradish peroxidase (HRP). Cholesterol within the sample is converted to hydrogen peroxide by two enzymes (cholesterol esterase, and cholesterol oxidase) immobilized on the chromatography paper. The hydrogen peroxide makes contact with a uniformly-coated dye in a distal region of the cassette (the Measurement Scale), and the hydrogen peroxide and the dye react with the HRP to form a purple color peak. Once the chemical reactions begin, a color change is visible at the proximal end of the paper strip (the first window) to alert the clinician that the device is functioning properly. When the entire solution has reached the top of the Measurement Scale, an indicator produces a green color (seen through the second window) to signal that the assay is complete. The height of the color peak is proportional to the amount of hydrogen peroxide, and thus the concentration of cholesterol within the sample. The height (in millimeters) is converted to cholesterol (in mg/dL) via the use of a conversion chart that accompanies each cassette lot.
The assay is performed in four simple steps. The sample is obtained by finger lancing, the blood is applied to the well and allowed to filter, the tab is pulled to start the reactions, and lastly the results are read directly from the cassette.
* Robert Superko, M.D., F.A.C.S.M., F.A.A.C.V.P.R. is an Associate Professor at Stanford University, and Director of the Heart Cardiac Rehabilitation Center in Berkeley, CA. Kathy Berra, B.S.N., F.A.A.C.V.P.R. and Cindy Rudd,
B.S.N., F.A.A.C.V.P.R. direct the YMCA Cardiac Therapy Medical Research Program in Palo Alto, CA.
2641 La Mirada Drive, Vista, CA 92083, USA Tel. 760-599-6555 - Fax. 760-599-1213
In addition to the comparative clinical study, an ancillary study was conducted to evaluate the precision of the AccuMeter. Two levels of a commercially available control were assayed 20 times to determine the within-run precision of the device, while run-to-run precision was evaluated by assaying duplicate cassettes in 34 runs. In all cases, the coefficient of variation (CV) remained between 4.1% and 4.6%. The specifies concerning AccuMeter precision may be found in the following tables.
Run-to-Run Precision
n=34 runs
Run-to-run precision was determined by field testing 2 controls in 34
runs.
The mean, standard deviation and coefficient of variation were calculated.
In conclusion, the AccuMeter met the interim guidelines established by the NCEP's Laboratory Standardization Panel for Cholesterol Measurement by demonstrating a level of accuracy within 5% or less. The performance of the device has been established; the next step is to assess the clinical utility of this easy-to-use, low-effort system. It is postulated that frequent and immediate patient feedback might enhance motivation and compliance with diet, exercise, and/or drug therapy to meet the objective of lowering cholesterol levels.
The clinical performance of the AccuMeter was evaluated in three diverse clinical settings: a physician's office, a cardiac rehabilitation clinic, and an industrial work site. A total of 251 patients with broad demographic diversity of age, gender, and cholesterol values (ranging from 123 mg/dL to 372 mg/dL) were included in the study. A detailed description of age and gender is provided below
Gender Male 127
Female- 124
Age (years) <20 1
20-35 74
36-49 74
50-64 56
>65 38
Unknown 8
Fingerstick specimens from each patient were assayed by both the AccuMeter and Abbott Vision(R) (Abbott Laboratories, Chicago, IL) analyzer. The Vision method was chosen as previous studies have shown the instrument to be an accurate fingerstick analyzer for total cholesterol measurement. Concomitantly a standard glass tube (10-15ml) of blood was drawn by venipuncture for serum cholesterol determination by the Abell-Kendall Reference (A-K) assay. Inclusion of the A-K method ensured that the results could be traced to the NRS/CHOL.
The inclusion of these three methods provided comparisons and correlations between AccuMeter/Vision, and AccuMeter/A-K. The following least-square linear regression equation was obtained for AccuMeter vs. Vision (AccuMeter on the y axis) y = 1.024x - 2.867 mg/dL. The correlation coefficient was 0.95, and the maximum estimated bias did not exceed 2%. Similarly, the least square-linear regression equation computed when AccuMeter was compared to A-K was: y = 0.991x + 0.394 mg/dL. The correlation coefficient was 0.96, and the maximum estimated bias did not exceed 1%. Thus, the AccuMeter demonstrated excellent accuracy as compared to both an instrumented device of similar technology (the Abbott Vision), and the accepted A-K reference method. A graphic representation of the AccuMeter accuracy as compared to the A-K reference method is shown below.
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