Abbott i-STAT 1 System Manual page 529

then decrease and plateau. β-hCG circulates as the intact molecule in the serum of women who have
an uncomplicated pregnancy. The subunits are cleaved rapidly and cleared by the kidneys.
availability of sensitive quantitative assays for the measurement of β-hCG, it has been shown that hCG
levels can be useful in prediction of spontaneous abortions,
pregnancy and multiple gestation.
7,9,10
The rapid and accurate diagnosis of pregnancy is commonly required by clinicians. Females of child-
bearing age frequently present to emergency departments (EDs), urgent care centers, physician
offices, clinics and other care providers with symptoms of pregnancy or other clinical conditions such as
abdominal pain, vaginal bleeding, syncope or shock -- conditions that may be pregnancy-related. During
pregnancy, many common medications are contraindicated, and diagnostic imaging is avoided if possible.
It is often necessary to determine rapidly whether women are pregnant, and the menstrual history alone
is not reliable. For these reasons, clinicians may require a rapid, quantitative β-hCG test at the point of
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care .
erformance Characteristics
P
Precision
The i-STAT β-hCG assay is designed to have a precision of <10% (CV).* A precision study was
performed following CLSI EP5-A2.
days using three different cartridge lots for a total of 80 results per control level per cartridge lot. The
average statistics are presented below:**
Control
Mean, IU/L
Level
1 20.8
2 725.3
3 1064.1
* The precision at lower levels is limited by a background imprecision designed to be ≤1.4 IU/L.
** Representative data; results in individual laboratories may vary from these data.
Method Comparison
Method comparison data were collected using CLSI guideline EP9-A2.
plasma samples containing β-hCG were spiked into venous whole blood samples collected in heparinized
evacuated tubes and analyzed in duplicate on the i-STAT System. A portion of the sample was
centrifuged and the separated plasma samples were analyzed in duplicate on the i-STAT System and the
Architect system within 4
Deming regression analysis 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, and 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 will vary from site to site due to differences in sample handling, comparative method
calibration and other site-specific variables.
***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."
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.
Rev. Date: 24-Jan-17
7
Three levels of control were tested in duplicate, twice a day, for 20
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Within-day,
%CV
5.3%
3.0%
4.0%
hours of collection.
Art: 730474-01D
aiding in the detection of ectopic
7,8
Between-
Total %CV
day, %CV
0.4% 5.5%
0.6% 3.7%
0.9% 4.2%
Commercially available frozen
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With the
6
The
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β-hCG
- 3