We have evaluated the cardiac troponin I (cTnI) enzyme
immunoassay AIA-PACK cTnI 2G (Tosoh Bioscience).
The interassay precision at different cTnI levels (0.30
6.70 ng/ml-1) showed coefficients of variation (CV)
between 5.00% and 4.71% on the AIA 600 II instrument.
These data are in accordance with the functional sensitivity
(0.04 ng/ml-1) and analytical sensitivity (0.02 ng/ml-1) specified by the manufacturers.
Comparative troponin I measurements in serum samples
were performed on the AIA-600 II analyser (Tosoh
Bioscience) and the Dimension RxL analyser (Dade Behring).
The cTnI concentration of serum samples (n=226)
ranged from 0 ng/ml-1 to 114 ng/ml-1. Regression analysis
of the cTnI values obtained showed a close correlation
between both results (RxL=0.96 AIA+0.38;
To induce proteolytic in vitro degradation of the cTnI
molecule, patient serum samples (n=20) were incubated
at 37C for 24 h and the cTnI concentration was determined
before and after the incubation with both analysers.
The cTnI concentration measured with the AIA-600
II analyser showed nearly identical values before and
after the incubation period. However, cTnI measured with the Dimension RxL analyser showed decreased cTnI values
in a range of 10 to 50% after the incubation period.
The AIA-PACK cTnI 2G assay uses two different monoclonal
antibodies against two epitopes in the proteolytic
stable region of the cTnI molecule (between position 40
and 90 of the cTnI amino acid sequence). Therefore,
measurement of cTnI in serum remains precise and specific in spite of in vitro proteolysis.