Troponin I Cutoff on Beckman Coulter Analyzers
Saturday, February 09, 2008
Cardiac troponins have become the preferred laboratory tests for the diagnosis of myocardial injury. Clinical and laboratory associations have endorsed the implementation of the 99th percentile reference value for cardiac troponin I for the detection of myocardial ischemia. Elevation of cTnI above the 99th percentile has become the definition of non ST-elevation myocardial infarction. Several recent articles have published the 99th percentile values for second generation cTnI in plasma.
In 2004, Panteghini etal (Clin Chemistry 2004;50:327-32) determined that the 99th percentile for the Beckman Coulter Access Accu TnI on the Access 2 instrument was 0.04 ng/mL (ug/L). This finding was later confirmed by Apple and Murakami in 2007 on a large study of almost 5000 specimens from apparently healthy individuals (Clin Chemistry 2007;53:1558-9).
Our health system has a mixture of Beckman Coulter Access 2 and DxI analyzers, which have very similar performance characteristics. For this reason, our laboratory adopted 0.04 ng/dL as the 99th percentile for cTnI system wide. After almost one year of operation, some interventional cardiologists commented that they were seeing too many with slightly elevated cTnI in patients without discernable ischemic heart disease. A subsequent analysis of cTnI results of healthy individuals participating in an annual health fair revealed that the 99th percentile was actually 0.07 ng/mL. Accordingly, the cutoff point for cTnI was immediately changed from 0.04 to 0.07 ng/mL.
Our experience emphasizes that clinical laboratories definitely need to determine their own 99th percentile for cTnI. Values calculated by carefully controlled research studies may be lower than those obtained by a busy clinical laboratory that does not have as tight of control over specimen collection, transportation and processing.
posted by Fred Plapp @ 1:20 PM,
