Comment To: Extensive Analytical Evaluation of the Performances of the New DiaSys PCT Assay and Comparison with Elecsys B·R·A·H·M·S PCT Test on Roche Cobas and B·R·A·H·M·S PCT-sensitive Kryptor

With great interest we read the article on “Extensive analytical evaluation of the performances of the new DiaSys PCT assay and comparison with Elecsys B·R·A·H·M·S PCT test on Roche Cobas and B·R·A·H·M·S PCT-sensitive Kryptor”, recently published in Clinical Chemistry and Laboratory Medicine [1]. The authors present the deep analytical performance evaluation of the PETIA-based procalcitonin test by DiaSys DiagnosticGmbH(Holzheim,Germany), investigating themain analytical parameters (LOQ, linearity, precision, and sample method comparison). The DiaSys PCT assay was reported to have good analytical performances and good agreement with the B·R·A·H·M·S-licenced methods by Roche Diagnostics GmbH and Thermo Scientific at concentrations ≥0.50 μg/L. However, at lower concentrations, the agreement was reported to be poor, and imprecision significantly higher. In this comment, we would like to point out several aspects, which we consider relevant in regard to the reported data and the understanding the importance of the widespread availability of this parameter and its standardization. The authors in some cases report better assay’s performances than those given by the test manufacturer itself (linearity [80 μg/L vs. 50 μg/L] and limit of quantitation [0.18 μg/L vs. 0.25 μg/L]). On the other hand, they report higher imprecision than that described by previous works [2, 3]. This may be explained by the fact that different protocols have been used to evaluate imprecision (5vs. 20-day protocol for previous works and the present one, respectively). It seems likely that further variability sources have been encompassed in the present evaluation. Additionally, no information is reported about the PCT concentrations, which the imprecision was measured at, so the comparison with the two B·R·A·H·M·S assays is partially hindered. The method comparison of the new DiaSys PETIA procalcitonin test shows to be suitable for sepsis diagnosis purposes (cut-off ≥0.5 μg/L), contrary to what previously was reported by the same authors in regard to a PETIA-based immunoassay by a different manufacturer [4] (Figure 1A). The statistically significant constant systematic error, evident in Figure 1B, could explain the lower medical concordance (Cohen’s kappa) between the tests at concentrations <0.5 μg/L. However, it should be mentioned that this may be ascribable to the lack of commutability for the calibrators [5] more than to the used tests themselves. The three specific samples, used by Di Deo-Vantaggiato et al., showing a significant difference in PCT quantification by the PETIA test in comparison to the BRAHMS tests, may also deserve a dedicated comment. The associated clinical background or further microbiological analysis of these samples are not provided by the authors. This hinders, as already stated by authors, the final interpretation. The authors state that these samples were stored frozen at −80 °C. The DiaSys procalcitonin test is based on the homogenous PETIA technology, which can be influenced by possible *Corresponding author: Prof. Dr. Matthias Grimmler, DiaSys Diagnostic Systems GmbH, Alte Straße 9, 65558 Holzheim, Germany; and Institute for Biomolecular Research, Hochschule Fresenius gGmbH, University of Applied Sciences, Limburger Str. 2, 65510 Idstein, Germany, Phone: +49 (0) 6432 9146 486, Fax:+49 (0) 6432 9146 167, E-mail:matthias.grimmler@ext.hs-fresenius.de. https://orcid.org/0000-0003-2860-3391 Thomas Masetto, DiaSys Diagnostic Systems GmbH, Holzheim, Germany; and Institute of Molecular Medicine I, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany. https://orcid.org/0000-00019609-3405 Clin Chem Lab Med 2023; aop