Circulating Immunoreactive Cardiac Troponin Forms Determined by Gel Filtration Chromatography after Acute Myocardial Infarction

BACKGROUND: Cardiac troponin I (cTnI) and cTnT measurements are used in the diagnosis of acute myocardial infarction (AMI). Together with troponin C (TnC), the cTnI and cTnT forms make up the ternary cTnT-cTnI-TnC (TIC) complex found within myocardium. Whether cTn occurs in the circulation after AMI as ternary TIC, binary cTnI-TnC (IC) complexes, or free troponin forms has not been thoroughly investigated. METHODS: Blood samples from 10 AMI patients were collected at hospital admission and then at 12, 24, and 48 h after onset of chest pain. Serum was subjected to gel filtration chromatography and cTnT (Roche cTnT) and cTnI (Siemens Centaur UltraTnI and Beckman Access AccuTnI) concentrations were measured in the gel filtration chromatography fractions. RESULTS: cTnT was present predominantly as free cTnT and cTnI as binary IC complex. These 2 forms were present at every time point. Lesser quantities of TIC complex (6%-32% of total cTnT and <50% of total cTnI) were detected in 4 patients at varying times. Minor quantities of a high molecular mass form of cTnI were detected occasionally. No free cTnI was found. Both cTnI assays identified a similar pattern of cTnI forms. CONCLUSIONS: After AMI, cTnI is present in serum as TIC and IC complexes. cTnT may be present as a combination of TIC and free cTnT or exclusively as free cTnT.