Discordant diagnoses of acute myocardial infarction due to the different use of assays and cut-off points of cardiac troponins

Objectives: Several assays for the measurement of cardiac troponin (cTn) are available, but differences in their analytical performances may affect the diagnosis of acute myocardial infarction (MI).

Methods: A survey was conducted at all Danish departments of clinical biochemistry at hospitals receiving patients with suspected acute MI to gather information about the assay and cut-off value used. cTn was measured in blood samples from 574 patients enrolled into the Odense Chest Pain Biobank with 3 different assays: the 4th generation cTnT (cTnT(4th)), high-sensitivity cTnT (cTnT(hs); Roche Diagnostics) and cTnI (Abbott Diagnostics). To evaluate concordance, patients were dichotomised according to the 99th percentile value for each assay. Additionally, a cut-off at 50 ng/l for cTnT(hs) was used, as this is the currently employed cut-off point in Denmark.

Results: Using a cTnT(4th) cut-off value of >0.03 µg/l, 130 patients (23%) had potential MI. With the cTnT(hs) assay and cut-off values at 50 versus 14 ng/l, respectively, 136 (24%) versus 301 (52%) patients had potential MI. With the cTnI cut-off point, 205 patients (36%) should be considered as having had an acute MI.

Conclusions: The use of different cTn assays and cut-off values may result in a discordant frequency of MI diagnoses. This makes efforts to harmonize cTn assays and cut-off levels mandatory.