Blood or spores? The difficult issue of interpreting cellular debris on human skeletal remains

Human skeletal remains are usually covered in debris: soil, leaves, insects but also by- products of decomposition. Among such debris, there may be, particularly around fractures elements of the hemopoietic system, such as red blood cells, which may be of interest. Regardless of their significance in diagnosing whether a fracture is vital or not, the identification of blood cells, fibrin etc. within or on a bone fracture is of great importance. The identification of traces of blood, in particular red blood cells, corresponds at least to a starting point. Many times, in historical and forensic contexts, the survival of red blood cells is mentioned and conclusions are drawn. But are we really looking at erythrocytes? Or do decomposition and debris hide or mimick important clues for the reconstruction of cause of death? These questions stemmed from several cases where elements very similar to blood cells were found in the context of lesions on skeletal remains and interpretation was almost impossible. Many of the commonly used techniques (such as optical microscopy, histology and immunohistochemistry) performed for the detection of such as cells may be inefficient in case of badly preserved remains. In addition, very little is known on how red blood cells degrade and what they may look like. With the intent to clarify the transformation of red blood cells and so facilitate their detection for a possible diagnosis of a vital bone lesion, the authors set out to test using Scanning Electron Microscopy the different morphology the red blood cell isolated from blood and left to decompose; in addition a Scanning Electron microscopy study was performed simultaneously on many different microscopic botanical structures (those found more frequently on human remains because derived from the external environment) with the aim of discovering what structures can mimic erythrocytes and what are the diagnostic features which could help in the discrimination. The results highlight the possibility to distinguish blood cells from botanical structures, in all their different morphological alterations, and permitted us to collect basic but precious knowledge. The use of SEM as a technique for the detection of blood cells in the diagnosis of the vitality of a bone lesion seems to be encouraging although it needs to be deeply investigated.