EFFECT OF COLLECTION AND PREPROCESSING METHODS ON NEUTROPHIL ELASTASEPLASMA-CONCENTRATIONS

Objectives: Elevated plasma levels of the elastase alpha(1)-proteinase inhibitor complex (E-alpha(1)PI) have been proposed as a marker of ba cterial infection and neutrophil activation. Liberation of elastase fr om neutrophils after collection of blood may cause falsely elevated re sults. Collection methods have not been validated for critically ill n eonates and children. We evaluated the influence of preanalytical meth ods on E-alpha(1)PI results including the recommended collection into EDTA tubes. Design and methods: First, we compared varying acceleratio n speeds and centrifugation times. Centrifugation at 1550 g for 3 min resulted in reliable preparation of leukocyte free plasma. Second, we evaluated all collection tubes under consideration for absorption of E -alpha(1)PI. Finally, 12 sets of samples from healthy adults and 42 se ts obtained from critically ill neonates and children were distributed into the various sampling tubes. Samples were centrifuged within 15 m in of collection and analyzed with a new turbidimetric assay adapted t o routine laboratory analyzers. Results: One of the two tubes containi ng a plasma-call separation gel absorbed 22.1% of the E-alpha(1)PI con tent. In the remaining tubes without absorption of E-alpha(1)PI no dif ferences were observed for samples from healthy adult patients. Howeve r, in samples from critically ill neonates or children, significantly higher results were obtained for plain Li-heparin tubes (mean = 183 mu g/L), EDTA tubes (mean = 93 mu g/L), and citrate tubes (mean = 88.5 m u g/L.) than for the Li-hep tube with cell-plasma separation gel and n o absorption of E-alpha(1)PI (mean = 62.4 mu g/L, p < 0.01). Conclusio n: Contrary to healthy adults, E-alpha(1)PI results in plasma samples from critically ill neonates and children depend on the type of collec tion tube. Copyright (C) 1998 The Canadian Society of Clinical Chemist s.