Estimation of biological variability of inflammatory biomarkers EDN, suPAR and plasma calprotectin

Knowledge of intra-individual and inter-individual biological variation (BV) of a measurand is essential for its optimal use in clinical practice. This study estimated biological variation, reference change values (RCV), index of individuality (II), and analytical performance specifications (APS) for the inflammatory biomarkers eosinophil-derived neurotoxin (EDN), plasma calprotectin (pCalprotectin), and soluble urokinase plasminogen activator receptor (suPAR), for which prior evidence has been scarce. Twenty healthy individuals (15 women, 5 men; 25-60 years) were included. Blood samples were drawn weekly for eight consecutive weeks and identical preanalytical procedures were applied at each visit. Plasma samples were prepared within 1 h after blood sampling and stored at -80 °C until analysis in duplicates. suPAR was measured by turbidimetry (ViroGates A/S), whereas EDN and pCalprotectin were analyzed using fluoro-enzymeimmunoassay (Phadia GmbH). Data were evaluated for outliers, variance homogeneity, and steady-state conditions before analysis was performed using a linear mixed model applied to transformed data. Within-subject (CV_I) and between-subject (CV_G) BV, respectively, were: EDN 15.6% and 43.8%; pCalprotectin 24.5% and 55.0%; and suPAR 5.7% and 20.0%. Low indices of individuality were observed for all measurands, indicating the need for RCVs to guide clinical interpretation. This study is the first to report BV estimates with accompanying APS, II and RCV for EDN, suPAR and pCalprotectin.