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Clin Biochem. 2004 Jun;37(6):472-80.

An interfering component in cardiac troponin I immunoassays-Its nature and inhibiting effect on the binding of antibodies against different epitopes.

Author information

1
Department of Biotechnology, University of Turku, FIN-20520 Turku, Finland. susann.eriksson@utu.fi

Abstract

OBJECTIVES:

We recently reported on the occurrence of a common interfering factor (IF) that negatively affects determinations of cardiac troponin I (cTnI). The aim of the present investigation was to extend our initial finding by a detailed epitope-based determination of the location of IF and to reveal the approximate size and characteristics of IF.

DESIGN AND METHODS:

Two-site immunoassays using combinations of 16 monoclonal and 2 polyclonal cTnI antibodies and 1 monoclonal troponin C (TnC) antibody were used to measure the analytical recovery of cTnI or cTnI-TnC in serum samples. Gel filtration of serum samples containing IF was performed and the analytical recovery of cTnI in the fractions was determined. EDTA-plasma samples to which cTnI had been added and serum samples containing endogenous cTnI were also separated by gel filtration.

RESULTS:

The mean analytical recoveries of cTnI were 28.3% (range 7.5-55.1%) and of cTnI-TnC were 23.5% (range 8.7-51.8%) in samples containing IF when antibodies against midfragment epitopes of cTnI were used. The mean recovery of cTnI was 65.1% and 73.3% for antibodies with N- and C-terminal epitopes. Gel filtration of samples with low recovery of cTnI showed that the approximate molecular mass of IF was 50-200 kDa and that the cTnI elution profiles of samples containing IF were shifted towards higher molecular mass compared with samples with less IF.

CONCLUSIONS:

Antibodies against midfragment epitopes of cTnI are affected by IF to a considerable but variable extent, and the presence of IF can be demonstrated by gel filtration.

[Indexed for MEDLINE]

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