D-dimers are degraded by human neutrophil elastase

To see if D-dimers were degraded by human neutrophil elastase (HNE), cross-linked fibrin was obtained by adding thrombin to purified fibrinogen in the presence of calcium ions and factor XIII, and the fibrin clot subsequently degraded by plasmin. Thereafter, the supernatant containing fibrin degradation products was removed and incubated with HNE. D-dimer levels were measured by two rapid semiquantitative tests, a latex agglutination test and the Nycocard immunofiltration test, and a quantitative ELISA-method. With increasing incubation time, D-dimer levels as measured by the latex and Nycocard tests rapidly decreased and subsequently became undetectable, while the ELISA D-dimer values remained essentially unchanged. By using SDS-electrophoresis and immunoblotting, the degradation of plasmic derivatives of cross-linked fibrin by HNE was visualised. We conclude that in a purified system, D-dimers formed during plasmin mediated lysis of cross linked fibrin are further degraded by HNE. Such HNE degradation reduces the D-dimer concentration as measured by rapid semiquantitive tests, and may be partly responsible for discrepant results when using different D-dimer assays.