Aspects of preanalytical variation of lactoferrin and elastase/alpha 1-protease inhibitor complexes

A number of interesting applications of plasma elastase/alpha 1-protease inhibitor complexes (ELA-PI) and lactoferrin (LAC) have recently been suggested. However, the clinical utility of these components often seems to be low. This might be improved by minimizing the preanalytical variation, if possible. Therefore, we have evaluated the influence of various aspects of sampling and handling conditions on the results obtained when measuring ELA-PI and LAC. Blood samples from both healthy persons as well as patients, who had undergone laparotomy the day before, were investigated. We confirmed the previous observations of higher concentrations of ELA-PI and LAC in serum compared to plasma. This was more pronounced in patients than in healthy adults. In EDTA-blood the most important change was seen in samples from patients when stored at room temperature. In this situation increases of LAC concentrations of 50% and 100% following 2 and 5 h, respectively were found. This in vitro release of LAC was abolished when samples were stored on ice until centrifugation within 5 h. In contrast, a statistically significant increase in ELA-PI of 10% was observed following storage on ice for 2 h of blood specimens drawn from healthy persons. EDTA-plasma obtained by venous puncture following minimal stasis contained 10% higher concentrations of LAC compared to samples drawn from intravenous catheters, while no difference was observed in the case of ELA-PI. However, in one individual prolonged venous stasis resulted in larger differences of both LAC and ELA-PI. Different centrifugation conditions (1500 vs. 3000 x g; room temperature vs. 4 degrees C) did not influence concentrations of LAC or ELA-PI measured, neither did eating a normal meal nor moderate physical activity (30 min walk). In conclusion, ELA-PI and LAC should be measured in EDTA-plasma. Blood must be drawn by venous puncture applying minimal stasis or from indwelling venous catheters. Samples for measuring LAC must be stored on ice until centrifugation. Separation of plasma from cells should be performed as fast as possible, but storage for up to 5 h can be accepted.