Blood residue are the wet and dry remnants of blood, as well the discoloration of surfaces on which blood has been shed. In

forensic science Forensic science combines principles of law and science to investigate criminal activity. Through crime scene investigations and laboratory analysis, forensic scientists are able to link suspects to evidence. An example is determining the time and ...

, blood residue can help investigators identify weapons, reconstruct a criminal action, and link suspects to the crime. In archaeology, it can be used to detect of origin of blood stains on buried objects.

Forensic significance

Blood constitutes about eight percent of a person's weight (normally about five liters), and it circulates near the surface of the skin. Almost all trauma to the body, therefore, results in the shedding of blood. Its red color makes it readily apparent at crime scenes, and its residues are very difficult to completely remove. Blood residue has even been recovered from 100,000-year-old stone tools. Laboratory testing can reveal whether a substance is indeed blood, whether the blood is of animal or human origin, and the blood group to which it belongs. This allows investigators to include or exclude persons as perpetrators or victims. The antigens that allow blood group testing, however, deteriorate with age or improper storage.Robinson, 154. The

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

contained in blood, on the other hand, is less subject to deterioration, and allows near-certain matching of blood residue to individuals with DNA profiling techniques. Through bloodstain pattern analysis, information about events can also be gained from the spatial distribution of bloodstains.

Forensic procedure

Finding and documenting blood residue

Freshly dried bloodstains are a glossy reddish-brown in color. Under the influence of sunlight, the weather or removal attempts, the color eventually disappears and the stain turns grey. The surface on which it is found may also influence the stain's color. Crime scenes are normally carefully searched for blood residue. Flashlights held at an angle to the surfaces under examination assist in this, as do luminol sprays which can detect even trace amounts of blood. Presumptive tests exist with which blood can be distinguished from other reddish stains, such as of ketchup or rust, found at the scene. The search includes areas beyond the immediate crime scene where blood might have been wiped off or bloody fingerprints left, such as towels or doorknobs. At outdoor crime scenes, bloodstains may be recovered from the ground or from plant surfaces.Robinson, 153. The standard documentation of blood residue includes photographs and descriptions of form, color, size and position of each stain found. Overall photographs and sketches are also produced to show the relationship of the blood residue to other elements of the scene and to enable pattern analysis. Recently 3D imaging techniques have been tried for documenting and investigating bloodstains.

Collection and preservation

To collect samples for analysis, wet blood is collected with a syringe and stored in a tube with

anticoagulant An anticoagulant, commonly known as a blood thinner, is a chemical substance that prevents or reduces the coagulation of blood, prolonging the clotting time. Some occur naturally in blood-eating animals, such as leeches and mosquitoes, which ...

, or collected with absorbent fabric that is allowed to air-dry. Dried blood is scraped off with a blade, or collected with a moistened cotton-tipped applicator, a gel lifter or fingerprint tape. Bloodstained clothing and other items are generally wrapped in paper and shipped whole to the laboratory. To prevent deterioration, blood residue samples are stored under refrigeration and, in the case of stains, air-dried.

Archaeology

Analysis of blood residue is also an important technique in

archaeology Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. The archaeological record consists of Artifact (archaeology), artifacts, architecture, biofact (archaeology), biofacts or ecofacts, ...

, where this field is sometimes referred to as haemotaphonomy ( etymologically coming from the Greek ''haima'' for blood, ''taphos'' for

burial Burial, also known as interment or inhumation, is a method of final disposition whereby a dead body is placed into the ground, sometimes with objects. This is usually accomplished by excavating a pit or trench, placing the deceased and objec ...

, and ''nomos'' for

law Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior, with its precise definition a matter of longstanding debate. It has been variously described as a science and as the ar ...

). It particularly involves studies of the morphology of blood cell in blood stains deposited on different media. Haemotaphonomy has also been used to study blood residues on fragments of medieval manuscripts, and on the Shroud of Turin. The term ''haemotaphonomy'' was proposed in 1992. It was inspired by the word " taphonomy" introduced in

palaeontology Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geo ...

in 1940 by Ivan Yefremov. The focus of haemotaphonomy is the morphology of blood cells when blood is in the form of a stain. Therefore, its subjects of study are any specimens stained with blood. The study method of haemotaphonomy is the analysis of images obtained through a

scanning electron microscope A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that ...

(SEM). However,

confocal microscopy Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser scanning confocal microscopy (LSCM), is an optical imaging technique for increasing optical resolution and contrast (vision), contrast of a micrograph by me ...

is a practical alternative to an SEM when a very high level of detail of the bloodstain surface is not required.

References

{{reflist