Skeletal troponin I cross-reactivity in different cardiac troponin I assay versions.

Abstract Objectives To study the skeletal troponin I (skTnI) cross-reactivity of four different commercially available antibodies in four cardiac troponin I (cTnI) research assay versions having the same epitope specificity as evidenced by peptide mapping. Design and methods The four research assays all use two solid phase antibodies and one detection antibody attached to intrinsically fluorescent nanoparticles. Two alternative antibodies were used for one capture antibody and two for the detector antibody. The assays were evaluated in terms of analytical sensitivity and by determining assay cross-reactivity to skTnI. Additionally, regression analysis was performed by measuring a sample panel ( n  = 101) with all of the four assay versions. Results A false-positive cTnI concentration of > 7000 ng/L was measured with one of the assay versions, when serum was spiked with 500,000 ng/L skTnI. The corresponding observed cTnI values for the other three assay versions varied from 616 ng/L to 727 ng/L. Out of the 101 clinical samples assayed, five showed spuriously (3- to 148-fold) elevated cTnI values with the skTnI interference prone assay setup, but not with the other assay versions. According to our investigational skTnI assay, all five samples contained measurable amounts of skTnI (range: 5500–702,000 ng/L). Conclusions Two out of four cTnI antibodies tested cross-reacted vastly with skTnI but did not cause any notable interference unless paired together. Therefore, skTnI cross-reactivity should be carefully assessed when cTnI assay antibodies claimed to be cTnI specific are selected.