Clinical significance of low-positive troponin 1 by AxSYM and ACS : 180

We compared troponin I (Tnl) assays (AxSYM [Abbott]; ACS: 180 [Bayer]) in b lood samples with concentrations less than 10 ng/mL (< 10 mug/L). Discordan t results were evaluated by, linearity, studies and by testing for rheumato id factor Patients with discordant TnI results were compared with patients with concordant results and patients with negative TnI who had a new myocar dial infarction or died within 2 months of initial testing. Positive ThI cu toffs by AxSYM of and A CS: 180 were 0.7 ng/mL (0.7 mug/L) and 0.13 ng/mL ( 0.13 mug/L), respectively. We identified 173 specimens that were repeatedly positive by at least I assay: 143 specimens were positive by both assays. Twenty, samples positive for TnI ky AxSYM were negative by ACS:180, while 1 0 samples positive by ACS: 180 were negative by AxSYM. The discordant sampl es showed no evidence of interfering substances, including rheumatoid facto r Clinical follow-up showed that 26% of patients with elevated TnI by both assays, 33% with TnI positive only by AxSYM, 22% with TnI positive only ACS :180, and 8% with negative TnI by AxSYM encountered at least 1 clinical end point. Variable detection rates by, these assays for low-positive Tnl repr esent a clinically significant problem.