Sample Type and Storage Conditions Affect Calprotectin Measurements in Blood

Background: Calprotectin, a complex of calcium-binding proteins, is abundant in granulocytes. Increased levels of plasma calprotectinhave been found in patients with inflammatory and autoimmune diseases. However, a number of preanalytical factors may affect calprotectinmeasurement in blood samples. Methods: Twelve blood samples [4 tubes, 1 each of lithium-heparin (Li-heparin), EDTA, and serum] were drawn from each of 14 healthy individuals. To evaluate the effect of temperature and storage time in the lag time between collection and centrifugation, samples were kept for 2 h at 4 °C, 20 °C, or 37 °C, before centrifugation. Leukocyte, neutrophil, and monocyte counts were measured in EDTA samples on a Sysmex XN-10 hematology analyzer to investigate the relationship between calprotectinconcentrations and the granulocyte count. Results: Calprotectinmeasurements in EDTA samples were not influenced by temperature or time lag between collection and analysis. Compared to EDTA plasma, significantly higher calprotectinconcentrations were found in serum and Li-heparin plasma samples. Furthermore, calprotectinconcentrations increased in serum and Li-heparin samples when stored at higher temperatures. There was a linear relationship between the serum calprotectinconcentration and neutrophil count in EDTA whole blood. Conclusions: EDTA is the most suitable anticoagulant for determination of calprotectinin plasma, as this sample matrix does not seem to be affected by temperature or time between sample collection and analysis. Of particular note, neutrophil activation by either clotting or centrifugation should be avoided during the preanalytical process.