title: Negative interference in cardiac troponin I immunoassays from a frequently occurring serum and plasma component.
abstract: BACKGROUND
  Cardiac troponin I (cTnI) is a sensitive marker of cardiac injury, but cTnI assays, like other immunoassays, are susceptible to interferences. We evaluated the presence of interfering substances by measuring the recovery of cTnI added to samples from volunteers and from patients with acute coronary syndromes (ACS).
  
  
  METHODS
  We added a ternary complex of human cardiac troponin (30-500 microg/L) or cTnI from serum to samples from healthy volunteers and ACS patients. We measured cTnI with a two-site sandwich time-resolved immunofluorometric assay using two antibodies against epitopes in the central stable part of cTnI. We also analyzed 108 heparin-plasma samples from 16 ACS patients with this assay, with an assay based on four antibodies, and with two commercial cTnI assays, AxSYM and ACS:180.
  
  
  RESULTS
  In samples from both healthy persons and ACS patients, recoveries for our assay were 1-167% (range). Recoveries were increased by addition of an antibody with an epitope in the N-terminal region of cTnI to the solid phase and an antibody with an epitope in the C-terminal region as a second detection antibody. In 2 of 16 patients with ACS, normal cTnI concentrations found when measured with the original assay demonstrated clinically abnormal (up to 10-fold higher) results with the additional N- and C-terminal antibodies in the early phase of infarction. Both commercial cTnI assays also demonstrated clinically misleading, falsely low cTnI concentrations.
  
  
  CONCLUSIONS
  Some yet unidentified, variable component, present in the blood from healthy volunteers and ACS patients, interferes with the binding of antibodies against epitopes in the central part of cTnI used in two commercial assays. Our approach to supplement the mid-fragment cTnI antibodies with antibodies in the N- and C-terminal parts of the molecule in an experimental assay represents a step in resolving this interferent.
authors.affiliation: Department of Biotechnology, University of Turku, Tykistökatu 6A, FIN-20520 Turku, Finland. susann.eriksson@utu.fi
authors.forename: Susann
authors.initials: S
authors.lastname: Eriksson
authors.forename: Miia
authors.initials: M
authors.lastname: Junikka
authors.forename: Päivi
authors.initials: P
authors.lastname: Laitinen
authors.forename: Kirsi
authors.initials: K
authors.lastname: Majamaa-Voltti
authors.forename: Henrik
authors.initials: H
authors.lastname: Alfthan
authors.forename: Kim
authors.initials: K
authors.lastname: Pettersson
mesh_terms: D000208:Acute Disease; D000906:Antibodies / Q000737:chemistry; D002138:Calibration; D003327:Coronary Disease / Q000097:blood / Q000175:diagnosis; D000939:Epitopes; D005188:False Negative Reactions; D015200:Fluoroimmunoassay; D006801:Humans; D009942:Organometallic Compounds / Q000737:chemistry; D013997:Time Factors; D019210:Troponin I / Q000097:blood* / Q000276:immunology
chemical_list: D000906:Antibodies; D000939:Epitopes; D009942:Organometallic Compounds; D019210:Troponin I; C475854:europium(III) chelate-2,2',2'',2'''-((4-((4-isothiocyanatophenyl)ethynyl)pyridine-2,6-diyl)bis(methylenenitrilo))tetrakis(acetic acid)