High incidence of discrepancies in new Siemens assay - A comparison of cardiac troponin I assays

OBJECTIVES: Cardiac troponin (cTn) is the biochemical gold standard for diagnosing myocardial infarction (MI). We compared the Siemens ADVIA Centaur High-Sensitivity (hs-cTnI) assay with the Siemens Ultra assay (cTnI-U).

METHODS: Over 3 months cTnI-U and hs-cTnI were measured simultaneously at Herlev-Gentofte Hospital. Acute myocardial injury was diagnosed using the 4th universal definition. Disputed cases were adjudicated using clinical data. We compared diagnostic accuracy using area under the curve (AUC) of the receiver operating characteristic. Outliers in between-assay differences were defined as a factor-5 difference and ≥1 measurement >40 ng/L. Patients with outlier differences were invited for re-sampling and tested with serial dilution and heterophilic blocking tubes.

RESULTS: From the 18th January to the 20th April 2019, 4,369 samples on 2,658 patients were included. cTnI-U measured higher concentrations than hs-cTnI (mean 23%, -52-213%), resulting in a higher frequency of acute myocardial injury, 255 (9.6%) vs. 203 (7.6%), p<0.001. This remained significant after adjudication, 212 vs 197, p<0.001. AUC for the prediction of MI for was 0.963 for cTnI-U and 0.959 for hs-cTnI, p=0.001. Outlier differences were seen in 35 (1.2%) patients, primarily with elevated hs-cTnI (n=33, 94%). On two re-samplings (median 144 and 297 days since inclusion), 16 of 20 (80%) and 11 of 11 had sustained elevation of hs-cTnI. The samples showed no signs of heterophilic antibodies.

CONCLUSIONS: Using hs-cTnI resulted in a subset of patients with large, discrepant elevations in concentration. These patients still had elevated hs-cTnI 6-10 months post admission but no heterophilic antibodies.