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Comparison of cardiac troponin I in serum and heparin plasma with the dimension RxL assay.

Cardiac troponin [I (cTnI) and T (cTnT)] assays in blood have rapidly become alternatives to older methods for detecting myocardial damage (1)(2). Furthermore, the recently redefined criteria for myocardial infarction that are used to classify patients with acute coronary syndrome have been established on the basis of increased serum/plasma cTnI or cTnT (3). The National Academy of Clinical Biochemistry has recommended the use of plasma rather than serum as the specimen of choice (4), citing improved turnaround times and potentially avoiding incomplete serum separation that may influence some methods to produce falsely increased results (5). However, some studies have shown lower cTnI and cTnT concentrations in plasma than in serum (6)(7). Because heparin effects vary among different analytical methods, we performed a study to evaluate cTnI concentrations in plasma and serum specimens assayed on the Dimension RxL (Dade Behring).

We evaluated assay imprecision using lyophilized control sera with three different concentrations of cTnI (0.57, 5, and 15 μg/L) that were analyzed 10 times in one analytical run for the determination of within-run imprecision and 24 times on 24 different days for the determination of between-run imprecision. Our results confirmed the manufacturer’s claims that within- and between-run imprecisions (CVs) were 2.8–3.9% and 2.9–4.1%, respectively. The analytical sensitivity was …