Abbott i-STAT 1, System Manual

Page: 503 / 658

Rev. Date: 23-May-12 Art: 715595-00R
cTnI - 3
exam) and ECG should be used in conjunction with troponin in the diagnostic evaluation of suspected
myocardial infarction.
3
A serial sampling protocol is recommended to facilitate the identification of temporal
changes in troponin levels characteristic of MI.
2,3,11
Since cTnI is not unequivocably detectable by commercial assays in samples from healthy persons,
measurements beyond the upper limit of the reference range have a significant probability of being
associated with ischemia or necrosis;
12
this probability increases with the measured troponin concentration.
Nonetheless, by definition, results beyond the reference range will occur in a normal population in healthy
individuals in the absence of myocardial necrosis, i.e. a result beyond the 99th percentile does not confirm
the presence of troponin with absolute certainty. Each institution should determine the reference range and
decision levels appropriate to its specific patient population and clinical practice.
Acute myocardial injury is evidenced by temporal changes in troponin levels while consistent elevations
of troponin may be suggestive of other chronic cardiac or non-cardiac conditions. There are many clinical
conditions that can lead to an elevated troponin level without ischemic coronary artery disease. Such
conditions include blunt trauma, myocarditis, congestive heart failure, left ventricular hypertrophy etc.
13,14
These clinical conditions should be considered when interpreting results. The use of serial sampling with
a consistent troponin methodology can identify temporal troponin changes, as well as provide additional
information that can assist in the clinical diagnosis for those patients with low-level results. Where there are
inconsistencies in the clinical information or where diagnostic criteria are not fully satisfied, the possibility of
biased results should be recognized – see Test Limitations.
Performance Characteristics
Precision data were collected in multiple sites as follows: Duplicates of each control were tested daily for a
period of 20 days, resulting in a total of 40 replicates. The average statistics are presented below.
Method comparison data were collected using CLSI guideline EP9-A2.
15
Venous blood samples were
collected in heparinized 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 comparative method
within 1 hour of collection.
Deming regression analysis
16
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 will vary from site to site due to differences in sample handling, comparative method
calibration and other site specific variables.
Interference studies were based on CLSI guideline EP7.
17
*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”.
13
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 (ng/mL)
Control Mean SD %CV
Level 1 0.53 0.04 7.8
Level 2 2.17 0.18 8.5
Level 3 31.82 2.42 7.6