![]() ![]() Having such a higher-order measurement system will pave the road toward the standardization/harmonization of PCT assays, which has been considered a high priority by the International Consortium for Harmonization of Clinical Laboratory Results. Moreover, the traceability of the results to SI units has not yet been established. Some assays were harmonized through traceability to the Brahms PCT LIA assay, but this protocol was not adopted for all assays. (13−15) Such a higher-order reference measurement system is still missing for PCT. (12) A proposed route to improve comparability and accuracy of the results is developing reference calibration materials, which have been value-assigned with a higher-order reference measurement procedure (RMP). However, the source of such variability remains unclear. (8−11) These discrepancies may impact clinical decisions at cut-offs, leading to disease misclassification and inappropriate antibiotic treatment decision. (7) Different studies underlined discrepancies of results provided by various commercially available PCT assays. Facing a growing demand for PCT testing, the number of commercialized assays based on different technical principles has increased considerably in recent years. (4−6) Thus, reliable and accurate measurements of this biomarker are critical for sepsis diagnosis, guiding treatment decisions, and patient monitoring. PCT measurement has been integrated into clinical guidelines and antimicrobial stewardship programs. (1−3) Different clinical decision cut-offs were established (e.g., 0.5 μg/L for sepsis diagnosis and 0.25 μg/L for antibiotic initiation or discontinuation for a patient with moderate or mild illness outside ICU (4)). Procalcitonin (PCT) is a recognized sepsis biomarker allowing patient stratification and antibiotic therapy management. Overall, this candidate RMP will support reliable sepsis diagnosis and guide treatment decisions, patient monitoring, and outcomes. The candidate RMP will also be used to evaluate whether the correlation between the candidate RMP and immunoassays is sufficiently high. This candidate RMP is fit to assign target values to secondary certified reference materials (CRMs) for further use in external quality assessment schemes to monitor the accuracy and comparability of the commercially available immunoassay results and to confirm the need for improving the harmonization of PCT assays. A recombinant PCT used as a primary calibrator was characterized by high-resolution mass spectrometry and amino acid analysis to establish traceability of the results to the SI units. ![]() The candidate RMP was successfully applied to the absolute quantification of PCT in five frozen human serum pools. Intraday precision was below 5.1%, and interday precision was below 4.0%. Intraday bias was between −3.3 and +5.7%, and interday bias was between −3.0 and −0.7%. The method allows quantification of PCT from 0.25 to 13.74 μg/L ( R > 0.998) with extension up to 132 μg/L after dilution of samples with PCT concentration above 13.74 μg/L. An antibody-free candidate reference measurement procedure (RMP) based on the isotope dilution mass spectrometry and protein calibration approach was developed and validated to quantify PCT in human serum. Variability of results in commercial assays has highlighted the need for standardization of PCT measurements. ![]() Procalcitonin (PCT) is a widely used biomarker for rapid sepsis diagnosis and antibiotic stewardship. ![]()
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