In forensic case work, blood stain pattern analysis frequently aids in deducing the chain of actions or parts thereof taking place during an event leading to blood loss. Wiped single blood stains and/or groups of blood stains are seen at a majority of complex crime scenes. The appearance of wiped blood stains depends on droplet volume and stain age (as a function of blood viscosity and the degree of stain skeletonization) and characteristics of the stained surface (i.e., texture, temperature). Furthermore, based on the biochemical and biophysical properties of blood, not only the drying processes, but also complex coagulation cascades are relevant to the assessment of wiped blood stains. This study was designed to determine if anticoagulation therapies markedly affect the wipeability of blood stains over times elapsed since deposition and the overall drying process. A total of 813 blood stains, originating from donors being treated with acetylsalicylic acid (ASA), clopidogrel + ASA, low-molecular-weight heparin, or rivaroxaban, were dropped on common household tiles. Wipeability at an ambient temperature of 20 °C was tested for 22 time periods (1, 2, 3, 5, 10, 15…105 min since deposition). Whereas stains consisting of untreated blood were dried within 55 min, wipeability of all droplets originating from donors with prior anticoagulation treatment showed pronounced delays compared with the control, ranging from 20 min (ASA and clopidogrel + ASA) to 45 min (rivaroxaban). This pronounced effect was not seen in earlier studies, which might be explained by the higher volume of droplets used in this study, which resulted in a shift in relevance from drying to clotting processes. Significant differences between the drying times of the various anticoagulation regimes might be attributed to anticoagulant activity against different targets in the coagulation cascades. In conclusion, anticoagulation treatment prior to blood loss significantly affected the wipeability of blood stains. Anticoagulation therapy should therefore be taken into account in the analysis of blood stain patterns.
