Method choice for investigation of macrotroponin interference with the Siemens Atellica high sensitivity troponin I
1Clinical Chemistry, Department of Pathology and Laboratory Medicine, Vancouver General Hospital, Vancouver, Canada; Department of Pathology and Laboratory Medicine, The University of British Columbia, Vancouver, Canada.
Objectives:
Macrotroponin refers to circulating immunoglobulin-bound cardiac troponin species that may elevate troponin results in patients with or without myocardial injury, causing diagnostic confusion. Clinical laboratories have been recommended to provide a service for troponin interference investigation. We evaluated the applicability of a Protein A/G IgG-depletion procedure as well as polyethylene glycol (PEG) precipitation for detecting macrotroponin interference with the Siemens Atellica troponin I (TnIH) assay.
Methods:
Troponin I, IgG, and albumin (internal standard) were measured (Atellica) on the neat and treated plasma to calculate recovery. Reference samples with TnIH ranging from < 1x to > 1000x times the 99th percentile were selected to verify expected recovery. To minimize likelihood of macrotroponin in the reference group, samples with elevated results were only included if recent acute changes in TnIH was documented. 40 samples were used for the IgG-depletion method and 20 for PEG precipitation. 25 samples from patients with unexplained elevation in TnIH were assessed by IgG-depletion.
Results:
38 of 40 reference group recoveries exceeded 70 % (median 91 %, IQR 15 %, max 129 %) in the IgG-depletion group consistent with literature on other assays. Specimens from patients with incongruent clinical picture had IgG-depletion recovery median of 11 % (IQR 14 %, max 37 %). PEG-precipitation showed large variation (median 103 %, IQR 89 %, max 227 %).
Conclusions:
IgG depletion using Protein A/G can reliably establish IgG-mediated interference with Atellica TnIH. PEG precipitation results are difficult to interpret likely due to matrix effects, especially at values closer to the 99th percentile.
