BACKGROUND: Proprotein convertase subtilisin/kexin type 9 (PCSK9) is involved in the regulation of LDL receptors. Inhibition of PCSK9 increase uptake of LDL-particles and pathogen-associated molecular patterns (PAMPs). The aim of our study was to evaluate biological variation of serum PCSK9. METHODS: Within-subject (CVI) and between-subject (CVG) biological variations were assessed in 14 healthy volunteers in a 6-week protocol (7 samples, equidistant time intervals). Serum concentration of PCSK9 was measured by a Quantikine ELISA assay (R&D systems, Bio-Techne Ltd., UK) on a DS2 ELISA reader (Dynex Technologies GmbH, Germany). Precision (CVA) was assessed by duplicate measurements. Two methods with different levels of robustness were used for the estimation of CVI, SD-ANOVA and CV-ANOVA method. We calculated the index of individuality and reference change values. The experiment was fully compliant with EFLM database checklist. RESULTS: The within-subject values of PCSK9 in healthy persons, as calculated by two statistical methods, were 23.2% (SD-ANOVA with CVA of 5.6%) and 26.6% (CV-ANOVA with CVA of 4.8%). The CVG was 10.9% (SD-ANOVA), index of individuality and RCV were 2.13 and 66.3%, respectively. CONCLUSIONS: The high index of individuality indicates that common reference intervals can be used to interpret serum PSCK9 values.

Department of Anesthesiology Resuscitation and Intensive Care Institute for Clinical and Experimental Medicine Vídeňská 1958 9 140 21 Praha 4 Czech Republic; 1st Faculty of Medicine Charles University Kateřinská 1660 32 121 08 Praha 2 Czech Republic

Institute for Clinical and Experimental Medicine Department of Laboratory Methods Vídeňská 1958 9 140 21 Praha 4 Czech Republic

Institute for Clinical and Experimental Medicine Department of Laboratory Methods Vídeňská 1958 9 140 21 Praha 4 Czech Republic; 3rd Faculty of Medicine Charles University Ruská 87 100 00 Praha 10 Czech Republic

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