False positive troponin result caused by a true macrotroponin

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A 35-year-old female presented with complaints of tiredness, shortness of breath and recent onset of chest pain. The cardiac troponin I (cTnI) concentration was elevated at 6.4 μg/L (Abbott Architect reference value: <0.03 μg/L) with a normal ECG. Physical examination, radiological imaging and routine laboratory investigations did not provide an explanation for the elevated cTnI concentration. Use of different troponin assays, dilutions with assay diluent, addition of mouse serum, polyethylene glycol (PEG) precipitation and gel filtration chromatography (GFC) were used to investigate possible interference. Troponin concentrations were below the level of detection when measured using all other troponin immunoassays. Serial dilutions of sample and addition of mouse serum did not alter the results. However, PEG precipitation and GFC showed the presence of a high molecular weight immunoreactive protein. Using GFC and protein-A IgG precipitation, the interference could be identified as a macrocomplex containing IgG and (fragments of) cTnI. We report a false positive cTnI result caused by a true macrotroponin, containing IgG and (fragments of) cTnI. This macrotroponin was only immunoreactive in the Abbott Architect cTnI immunoassay. Clinicians should be aware of analytical interference when troponin results are constantly elevated in the absence of (non)coronary causes of an increased troponin.