Outliers affecting cardiac troponin I measurement: comparison of a new high sensitivity assay with a contemporary assay on the Abbott ARCHITECT analyser.
BACKGROUND
False-positive cardiac troponin (Tn) results caused by outliers have been reported on various analytical platforms. We have compared the precision profile and outlier rate of the Abbott Diagnostics contemporary troponin I (TnI) assay with their high sensitivity (hs) TnI assay.


METHODS
Three studies were conducted over a 10-month period using routine patients' samples. TnI was measured in duplicate using the contemporary TnI assay in Study 1 and Study 2 (n = 7011 and 7089) and the hs-TnI assay in Study 3 (n = 1522). Critical outliers were defined as duplicate results whose absolute difference exceeded a critical difference (CD = z x √2 x SDAnalytical) at a probability level of 0.0005, with one of the results on the opposite side of the decision limit to its partner.


RESULTS
The TnI concentration at 10% imprecision (coefficient of variation) for the contemporary TnI assay was 0.034 µg/L (Study 1) and 0.042 µg/L (Study 2), and 0.006 µg/L (6 ng/L) for the hs-TnI assay. The critical outlier rates for the contemporary TnI assay were 0.51% (Study 1) and 0.37% (Study 2) using a cut-off of 0.04 µg/L, and 0% for the hs-TnI assay using gender-specific cut-offs.


CONCLUSIONS
The significant number of critical outliers detected using the contemporary TnI assay may pose a risk for misclassification of patients. By contrast, no critical outliers were detected using the hs-TnI assay. However, the total outlier rates for both assays were significantly higher than the expected variability of either assay. The cause of these outliers remains unclear.
PathWest, Royal Perth Hospital, Perth, Australia nicola.sawyer@health.wa.gov.au.
Nicola
N
Sawyer
PathWest, Royal Perth Hospital, Perth, Australia.
John
J
Blennerhassett
PathWest, Royal Perth Hospital, Perth, Australia.
Ramon
R
Lambert
PathWest, Royal Perth Hospital, Perth, Australia.
Paul
P
Sheehan
PathWest, Royal Perth Hospital, Perth, Australia.
Samuel D
SD
Vasikaran
D001774:Blood Chemical Analysis / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D012680:Sensitivity and Specificity; D019210:Troponin I / Q000097:blood*
D019210:Troponin I
Troponin; analytes