Comparison of cardiac TnI outliers using a contemporary and a high-sensitivity assay on the Abbott Architect platform.
BACKGROUND
Assays for cardiac troponin (cTn) have undergone improvements in sensitivity and precision in recent years. Increased rates of outliers, however, have been reported on various cTn platforms, typically giving irreproducible, falsely higher results. We aimed to evaluate the outlier rate occurring in patients with elevated cTnI using a contemporary and high-sensitivity assay.


METHODS
All patients with elevated cTnI (up to 300 ng/L) performed over a 21-month period were assayed in duplicate. A contemporary assay (Abbott STAT Troponin-I) was used for the first part of the study and subsequently a high-sensitivity assay (Abbott STAT High-Sensitive Troponin-I) was used. Outliers exceeded a calculated critical difference (CD) (CD = z × √2 × SDAnalytical) where z = 3.5 (for probability of 0.0005) and critical outliers also were on a different side of the decision level.


RESULTS
The respective outlier and critical outlier rates were 0.22% and 0.10% for the contemporary assay (n = 4009) and 0.18% and 0.13% for the high-sensitivity assay (n = 3878). There was no significant reduction in outlier rate between the two assays (χ(2) = 0.034, P = 0.854). Fifty-six percent of outliers occurred in samples where cTn was an 'add-on' test (and was stored and refrigerated prior to assay).


CONCLUSIONS
Despite recent improvements in cTn methods, outliers (including critical outliers) still occur at a low rate in both a contemporary and high-sensitivity cTnI assay. Laboratory and clinical staff should be aware of this potential analytical error, particularly in samples with suboptimal sample handling such as add-on tests.
Canterbury Health Laboratories, Christchurch, New Zealand Josh.Ryan@cdhb.health.nz.
J B
JB
Ryan
Canterbury Health Laboratories, Christchurch, New Zealand.
S J
SJ
Southby
Canterbury Health Laboratories, Christchurch, New Zealand.
L A
LA
Stuart
Canterbury Health Laboratories, Christchurch, New Zealand.
R
R
Mackay
Canterbury Health Laboratories, Christchurch, New Zealand.
C M
CM
Florkowski
Canterbury Health Laboratories, Christchurch, New Zealand.
P M
PM
George
D001774:Blood Chemical Analysis / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D012680:Sensitivity and Specificity; D019210:Troponin I / Q000097:blood*
D019210:Troponin I
Troponin; assay interference; false positives; high-sensitivity troponin; outliers