Forensic Serology 1

When police have a strong suspect in a murder case, the temptation is to leave it at that, to close down the search for a killer. But a few blood samples submitted to tests in the forensic laboratory can change the entire case!

Good blood cannot lie, they say. Nor can bad. As the distinguished forensic expert Alixtair R. Brownlie (Solicitor Supreme Courts, Edinburgh. Scotland) put it to Britain’s Forensic Science Society: “Since Cain slew Abel, spilt blood had borne its mute testimony in crimes of violence. Stains of blood and body fluids still play an important part in crime detection, a lesser but increasing part in the proof of guilt…” And not only the nature and grouping of stains, but their position at the scene of the crime can be revolving and is now recognised as a vital piece of evidence in itself.

The investigation of blood at a crime scene can be broadly divided into a biological approach (serology) and a physics approach (blood splatter or bloodstain pattern interpretation). This fact file will concentrate on the serological approach to blood evidence. Another fact file will cover the bloodstain pattern interpretation.

Blood is not the only body product, which can be of use to the forensic blood grouper. The word serology comes from the ancient Sanskrit sara, meaning, “to flow”. Today it is known that every fluid, which flows in the human body, can be identified: sometimes to prove the guilt of a suspected person, but also very often to protect the innocent. .

Essentially, forensic serology is based upon facts known vaguely since the dawn of time, and with much more certainty since in1628 the English physician William Harvey discovered the circulation of blood. Christopher Wren is said to have experimented with transfusion, and in his diary Samuel Pepys recorded that a donor was paid a sum of 20 shillings (about $500 in 1974 money), as well as speculating what would happened “were the blood of a Quaker to be let into an Archbishop”. For centuries the English aristocracy were genuinely believed to be born with blue blood, and boasts such as “the blood of an Englishman” were taken seriously.

Then, in 1930, the Viennese doctor Karl Landsteiner received a Nobel Prize award for his research into serology. He had announced to the scientific world that all human blood could be grouped into four main types. His work stimulated other biologists. Today for convenience the groups are known as O, A, B and AB.

Expert Evidence

While it should be remembered that it is never possible to say “this bloodstain originated from this person”; nevertheless it may be possible to conclude, “this bloodstain cannot have originated from that person”. A defence case may depend on this crucial fact. One striking example came to light early in September 1961 in England, when a 24 year old army private at Aldershot was cleared of sexual attack on a 38 year old mother.

“I can’t remember exactly what happened,” the woman said to the police “He jumped on me and got hold of my shoulders. I screamed as hard as I could ….. Then somehow I found I was at the bottom of a steep bank, and my little daughter was crying. The man had pulled off my blouse, but I gave up the struggle because he twice threatened to hurt my child ..”

False Identification

The doctor who examined the woman later confirmed there had been an attack. A solider was picked out at an identification parade, and charged with rape. Bryan Culliford, from the New Scotland Yard Laboratory, demonstrated that tests proved the suspect was in Group B, while the stains on the unfortunate woman were Group A. “We find there is no case to answer” announced the chairman of the court.

In her distressed state, the woman had picked out the wrong man at the identification parade. But for serology and its forensic application an innocent man could have been sent to jail.

Blood continues to play an important part in forensic investigations, and the discovery of new antibodies has enabled blood grouping techniques to be further refined. For example the Kell antigen is virtually confined to the white population, whereas the Duffy antigen is completely absent. Thus, blood grouping characteristics can be used to give an indication of race, and help to pinpoint the origin of bloodstains.

Forensic laboratories have researched sophisticated techniques for analysing protein in blood, and have been able to produce blood profiles with the prospect of establishing unique blood “fingerprints”. While this remains for the moment a serologist’s dream, blood continues to give up its secrets, and has described it as ‘a treasure trove of hidden clues’.

The first task in examining suspicious stains is to determine whether they are blood, and if so, are they human? Once this is established stains are examined for age, sex and blood group. The shape and pattern of liquid blood-splashes can help in reconstructing the murder; bloody fingerprints and palm-prints tell their own story; dried blood on a suspect’s clothing can be related to the victim, the crime scene and the murder weapon; blood and tissue forced under the fingernails of the victim during a violent struggle can be linked to the assailant.

Thus a single blood-trace can provide a wealth of information, and analytical techniques are improving all the time. For example, traces of drugs found in a bloodstain indicate medical treatment which a person might be receiving. While such procedures improve the scope of detection, it is not yet possible to identify an individual by his blood as it is by his fingerprints. Nevertheless, forensic serology, which in addition to blood deals with other body fluids such as saliva and semen, is important not only for narrowing suspicion on the guilty but also in showing a suspect’s innocence. As in many other aspects of forensic investigation, bloodstains are taken into account with a variety of other evidence to build up a pattern of crime.

A number of substances such as fruit-stains or dye-stuff may soil clothing and take on the appearance of bloodstains. The benzidine test – used for many years to confirm the presence of blood – has been discontinued because the reagent is carcinogenic. It has largely been replaced by the Kastle-Meyer test, using a solution of phenolphthalein which turns pink in contact with even small traces of blood. The test works by detecting the presence of the enzyme peroxides in the blood. However, as this substance is also present in other biological materials, the Kastle-Meyer test is regarded as a screening procedure. It is highly sensitive, and positive reaction is judged presumptive of blood, and further confirmatory tests are carried out. These are usually chemical and microscopically procedures to identify blood by its pigments and cellular structures.

Once a stain has been confirmed as blood it has to be determined whether it is human or animal. The precipitin test is used for this purpose. Blood of every animal species contains different proteins, and blood from one species will not accept proteins from a different species. Blood develops antibodies as a protective measure against disease and foreign matter to render them harmless. The serum containing antibodies produced by this reaction provides immunity from disease.

This principle is used to test whether blood-stains are human or not. Serum for the precipitin test is obtained from rabbits which have produced antibodies to destroy a small quantity of human blood injected into them. A drop of this anti-human serum is added to suspect blood, which will precipitate its protein if it is of human origin. Police laboratories hold anti-sera for most common animals, thus allowing the crime investigator to confirm or disprove statements made by the suspects about he origin of suspicious bloodstains. The precipitin test is sensitive, and will work on small traces of blood. The test is also known as the Uhlenbuth test after the German scientist who developed it in 1901.

The colour of dried blood changes in time from red to brown, and the peroxidise test takes longer to develop with an old stain. An experienced observer considering these factors might be able to give an opinion as to the age of a particular stain, but it is now possible to measure colour-change scientifically. Spectrophotometric analysis of bloodstains allows them to be aged within the range of one day to three weeks.

In 1949 two British scientists observed that the nuclei in the cells of female tissues usually contained a distinctive drumstick – like structure which was rare in males. This structure called a Barr bodies after one of its discoveries, is most noticeable in white blood cells and in the epithelial cells lining the mouth. Barr bodies are associated with the differences in chromosomes between males and females, and their appearance in blood of unknown origin is a basis for identifying it as from a female.

Determination of the blood group characteristics of stains found on clothing or a suspected murder weapon is another powerful link in the chain of evidence that can be built up in a case of violent death. Blood grouping is a developing science in its own right, and while it cannot provide information as certain as a fingerprint, it can provide circumstantial evidence establishing contact between a suspect and the victim.

Every person’s blood falls into one of the four international blood groups identified in 1900 by Dr Karl Landsteiner. The ABO blood grouping system is a function of the red blood cells, and the presence in them of a substance known as agglutinogen. A Group contains A agglutinogen B Group has B agglutinogen, AB Group contains both and O Group has neither. (What are anti-body reactions?) These factors are found in specific proportions among different populations.


O positive 40%
O negative 9%
A positive 31%
A negative 7%
B positive 8%
B negative 2%
AB positive 2%
AB negative 1%

What about other ethnic groups?

In 1927 Dr Landsteiner and a fellow-worker discovered further factors which occurred separately in human blood and were distributed in specific proportions among the population. These are the M. N. and MN factors, to which was added the P factor and in 1940 the Rhesus factor. The knowledge that each person’s ABO and MN blood group characteristics are inherited and fixed for life has made the examination of blood an important part of crime investigation. It is possible to place an individual in one of 288 different blood groupings, but forensic serologists are not able to say that a particular blood trace originated in a particular individual. The value of blood grouping procedures in crime work is that many potential suspects can be eliminated from an inquiry, thereby allowing the investigation to be narrowed down. About 80 per cent of the population are secretors which means that their blood cells are present in such body fluids as semen and saliva. It is possible, therefore, to determine blood groupings by examining these fluids.

Blood test

In criminology scientists do concern themselves with medical matters such as agglutination, but primarily the vital question involves whether or not a sample is blood. A minute sample in the laboratory is extracted from the stained material kept in a saline solution, and a tiny drop of the extract is mixed with a solution containing phenolphthalein and potassium hydroxide, powdered zinc and hydrogen peroxide. If this test is negative (no change), the sample cannot be blood. If the mixture shows a clear pink colour, it is blood.

Biologists sometimes use a different test, in which glacial acid is added to a solution of hydrogen peroxide and benzidine – a drop of this being added to the test sample, which immediately turns a deep blue if there is blood present. The next step is to use an antiserum prepared in an animal, which will react specifically with human blood, thus demonstrating whether the sample is of human origin.

“The blood of an Englishman” is not a subject over which forensic serologists wax racialist, because crime is international. The frequencies of the various genes within different blood group systems may, however, vary from race to race and could possibly provide important evidence. Blood group systems in general have acquired names such as Kidd, Duffy and Kell after the patients in whom the antibodies were first discovered, and all of them, of course, allow scientists to narrow down the field.

Summarizing all the international work of forensic serologist, the late Dr F.I.N. Dunsford, Ph.D. of Britain’s National Blood Transfusion Service, stressed that, in crime detection, the “usefulness” of a blood group system is the measure of its efficiency – differentiating the red cells of one person from those of another.

From his tests, for example, it is known that the Rhesus antigen V is present in fewer than 0.5 per cent of white people, but present in 40 per cent of West African Negroes. The chromosomes (the rod like structures which show as pairs in every developed cell) known as cDe are also more common among Negroes than whites.

The Duffy phenotype Fy is always completely absent from whites, but present in 90 per cent of West Africans. Kell antigen is virtually confined to white races, while Diego positives are virtually absent from whites, yet present in Caribe Indians, Japanese, and Chinese.

At the extreme of the blood group sis a certain LU (a _ b__) factor, which many serologists believe to be so rare that an estimated total of only eight people among the world’s 3200 million plus can have it. One of the eight, a Sheffield ( England ) woman, had three pints of the rare blood flown to her in a British hospital from an American donor.

More on blood type systems.

However, researchers maybe only on the threshold of discoveries in investigation of body fluids. It is now nearly 75 years since serologists put blood samples under the microscope and found the elements which are freely suspended in the plasma – essentially the erythrocytes (red corpuscles), leukocytes (white corpuscles), and the blood platelets (egg shaped and circular bodies suspended in the straw plasma more commonly known as the “serum”).

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