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Can serum and EDTA-plasma samples be used interchangeably for high sensitive troponin I measurement?

Background: Manufacturer (Beckman Coulter, USA) recommends serum, EDTA and Li-heparin plasma for high sensitive troponin I (hsTnI) measurement, with a conversion factor for serum values of 0.90 for 99th percentile upper reference limit (URL) of a healthy population when EDTA plasma samples are used. The aim of the study is to verify the manufacturer's claims for measurement of hsTnI in EDTA plasma samples. Materials and Methods: High sensitive TnI was measured in both serum and EDTA-plasma samples of 31 patients with suspected AMI admitted to our Emergency Department. Measurements were done by chemiluminescent method on DXI 600 (Beckman Coulter, USA) analyzer. The 99th percentile URL defined by manufacturer is 17.5 (12.6–20.7) ng/L. Method CV(%) at a lower reference limit of 99th percentile (12.2 ng/L) was estimated in accordance to CLSI EP15-A3 guideline. According to IFCC Committee on Clinical Applications of Cardiac Bio-Markers our acceptance criterion for method precision was ≤10 % for 99th percentile URL of a healthy population. The hsTnI concentrations were compared by nonparametric Wilcoxon test. P-value ˂0.05 was considered significant. Also, the comparability of results was assessed by linear regression. Statistical analysis was done in MedCalc Statistical Software v16.2.0 (MedCalc Software bvba, Ostend, Belgium). Results: Method precision at 12.2 ng/L was 8.55%. There was a statistically significant difference in median values (in ng/L) of serum [15.20 (9.53– 32.49)] and EDTA-plasma samples [12.30 (7.63– 26.89)], P<0.001. Median bias was 2.6 ng/L (95% Cl: 1.50-4.68). The regression coefficients were: 0.75 (95% CI:-1.80–3.29, P=0.554) for intercept, and 0.89 (95% CI: 0.8941–0.8952, P<0.0001) for slope. Conclusions: Our study confirmed the manufacturer's conversion factor of 0.90 for measurement of hsTnI in EDTA plasma samples. The serum and EDTA plasma samples for hsTnI measurement should not be used interchangeably.

hsTnI, sample, preanalytical phase

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