Capillary plasma neutrophil elastase alpha-1-proteinase inhibitor as infection parameter in neonates

Raised plasma neutrophil elastase has been reported to be an early and effective marker of infection in neonates. In order to assess the feasibility of implementing a rapid assay on capillary plasma, repeated heel prick samples were taken in a series of 79 neonates with clinically suspected bacterial infection, comparing the elastase response with C-reactive protein (CRP) and with the band:mature neutrophil ratio. Rises in elastase were in agreement with rises in CRP, but were more frequently manifest at onset of symptoms, showing elastase to be a more rapid marker of infection as previously described. However, 23% of elastase measurements either failed due to haemolysis or coagulation or yielded inexplicably high values. Comparison of simultaneous bilateral heel prick values confirmed unacceptable variation, unlike comparison of paired venous samples or venous and capillary samples from adults, indicating that capillary blood sampling in neonates produces an unpredictable release of neutrophil elastase. Thus, in newborn infants samples for determination of elastase should be taken by venous punctures or from indwelling catheters.