Circulating calprotectin as biomarker in neutrophil-related inflammation: Pre-analytical recommendations and reference values according to sample type

Background: Calprotectin (CLP) is a promising biomarker for the evaluation of neutrophil-related inflammation. Our aim was to establish reference values for circulating CLP in different sample types and to study the effect of pre-analytical variables. Methods: Reference values were determined in 100 healthy individuals. Pre-analytical variables were evaluated in 10 healthy controls and four rheumatoid arthritis patients with active disease and covered sample type (serum with/without gel separator, heparin, EDTA and citrate plasma), pre-centrifugation time (<2 h, 6 h, 24 h), storage condition (2-8 degrees C, 18-25 degrees C, 30 degrees C) and storage time (24 h, 72 h, 7 days). CLP measurements were performed with the EliA (TM) Calprotectin 2 assay on Phadia (TM) 200 (Thermo Fisher Scientific). Results: In healthy controls, baseline CLP concentrations in serum were more than double the concentration in EDTA and citrate plasma (0.909 mu g/mL versus 0.259 mu g/mL and 0.261 mu g/mL respectively). Heparin, EDTA and citrate stabilized CLP concentrations for up to 6 h before centrifugation, whereas significant increases in CLP levels were observed when serum was left untreated during that time period. Conclusion: Clinical studies on circulating CLP need to apply sample type-specific reference values and decision limits. To obtain reproducible CLP results in serum, more stringent pre-analytical sample handling instructions are needed.

Automated summary

The study aimed to establish reference values for circulating CLP in different sample types, and found that baseline CLP concentrations in serum were higher than in EDTA and citrate plasma. Pre-analytical variables were evaluated, showing that heparin, EDTA, and citrate stabilized CLP concentrations for up to 6 hours before centrifugation.