Rev. Date: 23-May-12 Art: 716969-00J BNP - 9
Method comparison data were collected using CLSI guideline EP9-A2.
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Venous blood samples were
collected in EDTA evacuated tubes and analyzed in duplicate on the i-STAT System. A portion of the
specimen was centrifuged and the separated plasma was analyzed in duplicate on the i-STAT System and
on the comparative method within 1 hour of collection. Deming regression analysis
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was performed on the
first replicate of each sample. In the method comparison table, n is the number of specimens in the first
data set, Sxx and Syy refer to estimates of imprecision based on the duplicates of the comparative and the
i-STAT methods respectively. Sy.x is the standard error of the estimate, and r is the correlation coefficient.*
Method comparisons may vary from site to site due to differences in sample handling, comparative method
calibration and other site specific variables.
The i-STAT BNP assay is designed for quantitation of BNP in whole blood or plasma samples. A series
of samples for comparison of whole blood and plasma results was prepared from blood drawn from
twenty-five nominally healthy donors. For each donor, whole blood (unspiked) and plasma obtained via
centrifugation were first run simultaneously in duplicate i-STAT BNP test cartridges. A whole blood sample
was then spiked with BNP and, following a short equilibration period, a plasma sample was prepared by
centrifugation and the whole blood and plasma samples were run simultaneously in duplicate. Three lots
of i-STAT BNP test cartridges were employed with a single lot being used for each donor. The results of
Deming regression of whole blood vs plasma (x-axis) correlation data are summarized below for all samples
( [BNP] < 5000 pg/mL) and separately for samples with [BNP] < 1000 pg/mL.
*The usual warning relating to the use of regression analysis is summarized here as a reminder. For any analyte, “if the data is a narrow range, the
estimate of the regression parameters are relatively imprecise and may be biased. Therefore, predictions made from estimates may be invalid”.
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The
correlation coefficient, r, can be used as a guide to assess the adequacy of the comparative method range in overcoming the problem. As a guide, the
range of data can be considered adequate if r>0.975.
Precision Data (pg/mL)
Aqueous Control Mean %CV (within-run) %CV (total)
Level 1 126 9.0 11.1
Level 2 1551 6.6 8.1
Level 3 3337 8.0 9.8
Method Comparison
Abbott ARCHITECT
N 433
Mean (pg/mL) 482.1
Sxx (pg/mL) 38.1
Syy (pg/mL) 97.6
Slope 0.971
Intercept -14.4
Sy.x 198.0
Xmin 5
Xmax 4797.7
Correlation, r 0.972
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