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Collection And Preservation Of Blood Evidence For Analysis In Crime Lab / Forensic Lab

Blood Evidence           

Blood refers to a highly complex mixture of cells, enzymes, proteins and inorganic substances. Based on Saferstein (2007), plasma is the fluid portion of blood which contains red blood cells (erythrocytes), white blood cells (leukocytes) and platelets. Meanwhile, antigens usually proteins on the surface of the blood cells are responsible for blood type characteristic. (Saferstein, 2007, p.347). Blood also has their own physical properties such as viscosity, density, surface tension and others. In elden days, blood may not a very useful clue in crime. However, at current times, blood is the most common evidence found in any crime scene.

In forensic field, blood evidence can be divided into dried bloodstain and wet bloodstain. Wet blood has more value than dried blood because more tests can be performed. For example, alcohol and drug content, particularly can be determined from wet blood only. But blood begins to dry after 3 to 5 minutes of exposure to air. As it dries, it changes color towards brown and black. There are more advantages for wet bloodstain evidence over dry bloodstain evidence. Schiro stated that it only needs a little storage space because it is in liquid form. However, the disadvantage is that evidence collector needs both stains and control where they also have direct interaction with bloodstain.

If wet blood evidence cannot available, based on Saferstein (2007), dried bloodstain should be obtained by removed from surface with a sterile cotton-tipped swab lightly moistened with distilled water. Then, the swab must be air dried.  (Saferstein, 2007, p.413). Advantage for dried bloodstain, Schiro stated that it requires a minimal amount of interaction with bloodstain because it is not in liquid form. Disadvantage, however, bulky blood evidence requires more storage space.

Figure 1 : Blood evidence at scene
(Source : www.advancedbio-treatment.com)

Method Of Collection and Preservation Of Blood From Body  

Based on Locard exchange principle, every contact leaves a trace. There are high possibility for blood to transfer between victim and suspect during a struggle.

For victims, they must undergo medical examination as soon as possible to collect physical evidence. Saferstein stated that for blood sample collection, a minimum of 20 milliliters is to be collected and put in a vacuum tube containing the EDTA preservative. The blood sample can be used for DNA test or toxicological analysis (Saferstein, 2007, p.374).

For dead body, it is the best to collect blood sample from different sites of body. Blood may be collected from heart, leg and arm. When blood is removed from individual body, it must be sealed in different airtight container after adding an anticoagulant and preservatives. Then, the blood should be stored in a refrigerator until delivery to laboratory.

Method Of Collection and Preservation Of Blood From Crime Scene  

The presence or absence of bloodstain often provides much information that can help investigation process. Laux explained that any stain at a crime scene that could be identified as blood should be identified. Bloodstains should never be contaminated with any reagent (Laux, 1991). Several precaution steps must be done to collect and preserve the bloodstain at a crime scene.

At the crime scene, evidence collector should take some simple steps during collecting blood sample to prevent or minimize contamination of blood sample. First of all, wear gloves prior to collection of the blood sample. Secondly, always package each item of evidence separately in its own well-ventilated container. Blood sample should not be packaged in plastic or airtight container because it can lead to the growth of DNA-destroying bacteria and fungi due to accumulation of residue moisture.

Quantity of blood at crime scene depends on the nature or texture of target surface. Bloodstains are more easily recovered from non-porous surface compare than porous surface. Blood evidence also must not be exposed to excessive heat.

Figure 2 : Swab technique in blood collection
(Source : imgarcade.com)

Types of Vacutainers   

Blood collection tubes are called vacutainer. Vacutainer is a sterile glass or plastic with a closure to create vacuum inside. There are many types of vacutainer to preserve the blood sample. Vacutainer tubes contain different additives to stabilize and preserve the blood specimen before analysis is being done at the laboratory. Vacutainer have different colour cap with different function. To contain blood sample, yellow, grey, purple, orange and red cap vacutainer can be used.

Grey cap container contains preservative or anti-coagulant such as sodium fluoride to prevent the growth of microorganism capable of destroying alcohol. Failure to keep the blood refrigerated or to add sodium fluoride causes decline in alcohol concentration. It is used for glucose and lactate test but not suitable for DNA analysis. This type of vacutainer cannot be kept frozen.

Purple cap vacutainer contains anti-coagulant such as EDTA (ethylenediamine tetraacetic acid). Anti-coagulant is a substance that prevents coagulation or clotting of blood. It will inhibit activity of enzymes that will degrade DNA. However, the vacutainer must be kept refrigerated but not frozen while awaiting transportation to laboratory.

Yellow cap vacutainer contains acid citrate as an additive. This type of vacutainer is used for analysis of blood DNA, serological test and acid phosphatase level. Orange cap vacutainer contains serum separation gel. This type ofvacutainer is used for serum determination.

Lastly, red cap vacutainer does not contain additives or anti-coagulant. It contains clot activator that is used to collect serum for chemistry test. It is useful for conventional serological tests such as for pregnancy and HIV testing, but not suitable for DNA testing. After sample is put inside the vacutainer, tube need to be inverted for 5 until 10 minutes to prevent blood from clotting.

Figure 3 : Types of Vacutainer
(Source : www.bio-x.in)

Transportation of Evidence to Laboratory       

Laboratory tests are more sensitive compare to the screening test that can be conducted at the crime scene. This is the reason why biological fluid evidence especially blood need to be sent to laboratory. Blood has great evidential value. Hence, blood on the clothing from both victim and suspect should be collected and sent to the laboratory for further examination. Laboratory examination is more revealing and sensitive compare to the search procedures that are conducted at the crime scene.

Before transporting evidence to the laboratory, all blood evidence should be examined to make sure that all sample is not lost during transportation process. Then it should be taken to laboratory as soon as possible. Usually, sample is sent to the laboratory by the police.

In laboratory, many chemical tests can be performed on the blood specimen collected from crime scene.  Example, the Castle Mayer colour test is used to determine the stain whether it is blood or not. For blood grouping, a test kit can be used to determine the main bloods groups, which are A, B, O and AB.

Storage Duration Of Evidence in Laboratory   

Evidence is stored at laboratory for different duration of time depends on types of sample and laboratory standard operation procedure.

Disposal of Evidence

Disposal means the return of evidence to the owner or organizations who request for a particular test. Certain laboratory has a set limit on the storage space to retain the sample within certain period of time. Then the evidence or sample will be returned with the final report or result of analysis.

Certain laboratory retains the evidence for a certain period of time before disposal of the sample.  These evidence at the time of disposal, are placed in biohazard bags according to the disposal procedure.

Precaution when Handling Blood Evidence     

Saferstein explained that the blood evidence must be collected with a minimum amount of personal contact to reduce contamination risk (Saferstein, 2007, p.413). All samples must be assumed to be infectious, so wearing gloves while handling the blood sample is required. Individual who handles blood specimen always need to change glove. It can reduce the possibility that evidence will be contaminated by evidence collector. Other safety procedure such a wearing of vest, face masks and shoe cover during collecting blood evidence are apllicable. Since blood evidence can provide information that may solve the criminal cases, chain of custody need to be maintained while handling blood evidence to ensure that the evidence collected at the crime scene to be similar with the evidence presented at the court. An accurate chain of custody identifies and tracks the evidence from the time it was collected. Thus all documentation must be done correctly.


  1. Laux, D. L. (1991). Effects of luminol on the subsequent analysis of bloodstains. Jurnal Forensic Science, 36, 1512-20.
  2. Saferstein R. Criminalistic : An Introduction to Forensic Science. London : Prentice Hall International (UK) Limited, 2004.
  3. Schiro, G. Collection and Preservation of Blood Evidence from Crime Scenes. Forensic Scientist Louisiana State Police Crime Laboratory. Retrieved February 24 2015 from http://www.crime-scene-investigator.net/blood.html.
  4. Vacuntainer. In Wikipedia online. Retrieved February 24, 2015, from http://en.wikipedia.org/wiki/vacuntainer.

Last Reviewed : 19 May 2015
Writer : Syed Ahmad Nazmi bin Sayed Mohamad
Accreditor : Khoo Lay See