Frequency of Antibody-Mediated Positive Interference in a Healthy Danish Cohort Using Combined Immunodepletion and Ultracentrifugation with a High-Sensitivity Cardiac Troponin I Assay.

BACKGROUND: Diagnosis of myocardial infarction relies in part on cardiac troponin (cTn) concentrations exceeding the 99th percentile upper reference limit. Positive antibody-mediated interference (PAI) occurs when anti-cTn antibodies form macrotroponin complexes with slow clearance or when heterophilic antibodies generate cTn-independent signals. PAI may inflate the upper reference limit and may increase the risk of missed myocardial infarction. We determined the frequency of PAI using the Abbott Alinity High-Sensitivity cTnI Assay and assessed its impact on the 99th percentile in a healthy Danish reference population. METHODS: In a cross-sectional cohort of 1053 healthy individuals used to establish Danish 99th percentiles, PAI was assessed in samples within the sex-specific highest 10% of cTn concentrations. Ultracentrifugation and immunodepletion were used to evaluate molecular weight and the effect of IgG removal on measured cTnI. Concordant results from both methods were considered confirmatory for PAI. Sex-specific 99th percentiles were recalculated after excluding individuals with confirmed PAI. RESULTS: A low-dilution combined ultracentrifugation and immunodepletion protocol enabled detection of PAI at cTnI concentrations as low as 3.5 ng/L. Among the 86 highest samples, 48 (56%) were classified as PAI, corresponding to an overall frequency of 4.6%. Exclusion of PAI reduced the 99th percentile from 45 ng/L to 10 ng/L overall, from 66 ng/L to 11 ng/L among men, and from 21 to 8 ng/L among women. CONCLUSION: PAI detected with our method that combines immunodepletion and ultracentrifugation is common and substantially inflates the 99th percentile for the Abbott Alinity High-Sensitivity cTnI Assay.