Thursday, September 25, 2008

Life Body Fluid: Serology

by Andrea Campbell

Our bodies have their own little rivers of fluid—namely, blood, saliva, semen, sweat, or fecal matter. Forensic serology is the study of these bodily fluids as related to legal matters. Under the umbrella of this biological body of knowledge, forensic serology scientists detect the presence of blood and study the enzymes and antigens present in red blood cells, or what could commonly be called “blood typing.” You may even know your own blood type whether it is A, B, O or AB in type. (There are also people with Rh-factor blood, another important antigen, and, another story.) Blood from different individuals may differ in the type of antigen on the surface of its red blood cells and the type of antibody in its plasma. Consequently, in a blood transfusion, if the blood groups of the donor and recipient are incompatible, a dangerous reaction occurs involving aggregation or the clumping of red cells of the donor in the recipient’s circulation.

We have about ten pints of blood (or up to six quarts of blood, half plasma and half blood cells) being circulated through our bodies by the circulatory system. The blood is pumped by and through the heart into vessels and veins and transports materials—nutrients such as glucose— and oxygen, to vital organs and tissues for growth and repair. It also carries carbon dioxide and waste products from the tissues for excretion. And hormones are taken to various tissues and organs for chemical signaling, all the while moving digested food from the gut to the liver, and within, too, are immune bodies that are hanging out for the prevention of infection, and which possess clotting factors to help stop bleeding to all parts of the body.

In some crime labs, forensic serologists also take on another hat and become expert in “blood pattern analysis,”—also referred to as
blood spatter—which is used to recreate the violent scenarios involved in a crime scene according to the patterns displayed on surfaces around the room.

Crime scene blood is important to real life detectives (and also to mystery writers), because it is often found as the result of homicide, assault and sexual assault. Since blood can be found at different time stages, it can be present as fresh liquid pools, coagulated blood, (meaning the blood has turned to a semi-solid state), dried blood, small drops, or even swiped stains.

When any dark substance is found at the scene it is carefully collected because many things can contaminate blood and it can act as a biohazard to the criminalist collecting it. That is why crime scene technicians will often suit-up wearing latex gloves, surgical masks, eye-cove
rings and sometimes full coverage gowns. (Yes, the CSI people on TV all have hepatitis according to the way they dress!) And although they might not wear as much PPE (Personal Protection Equipment) as shown in the picture at the right, they will surely wear booties, gloves and maybe even a mask.

The determination of blood is best made by using a preliminary color test and for years, the most commonly used was the benzidine color test. (Benzidine was labeled a carcinogen, so it has generally been discontinued.) The Kastle-Meyer color test was used in its place and basically, the tests are based on the fact that blood
hemoglobin possesses peroxidase-like activity. To simplify, these are enzymes that when tested with a reagent will cause the sample to turn a deep pink color. It’s not an absolute however, because potatoes and horseradish will also turn it pink.

Sometimes a powerful light moved across the surface of a crime scene is all that is needed for visual inspection. But if blood is suspected and not readily seen, luminol is sprayed and after about five seconds it will fluoresce in a darkened room. Luminol is prohibitive though, because it will destroy many important blood factors necessary for the forensic characterization of blood.

Microcrystalline tests can be performed on material and there are several tests available but the two most popular are the Takayama and Teichmann tests. These depend on the addition of specific chemicals to the blood so that characteristic crystals with hemoglobin derivatives will be formed. They will also react to other materials that may be present in a bloodstain.

After the blood is in the lab a test is used to find out
whether it is human or animal blood. It has to do with a rabbit and chicken egg proteins and it forms a cloudy substance called a precipitin. Another test can be done using a “gel diffusion” test. The sample’s antibodies and antigens will diffuse or move toward one another on an agar gel-coated plate. The extracted bloodstain and the human antiserum are placed in separate holes opposite each other on the gel. This will then be subjected to an electrical field and a specific reaction will be expressed by a line of precipitation formed between the two. The blood is then typed. In 1925, a special percentage of the human population were found to be “secretors,” which means that certain antigens, proteins, antibodies and enzyme traits can be found in other bodily fluids such as saliva, urine, or teardrops.

Today, DNA has replaced the tests for specific enzymes and proteins and while they are more accurate, they are also more expensive, timely, and require an updated crime lab facility. Sometimes it is about expertise, resources, and budget that determines how much bodily fluids are taken into consideration.


Gritsforbreakfast said...

Blood splatter "evidence" is mostly subjective pseudoscience when performed by "forensic serologists." The disciplines required to interpret splatters correctly lie FAR outside their field of expertise and even then usually the results aren't clear enough to be probative. Mostly it's junk science. It's often said splatter patterns can tell the difference between a murder and suicide, but according to a seminar presentation I heard recently, there's no real research-based support for that claim.

Anonymous said...

Some Medical Examiners (e.g., Bexar Co's Vincent DiMaio) would disagree with blood spatter evidence being labeled pseudoscience. Former police captain Tom Bevel, now an expert, would also disagree. And Bevel's no "hired gun." In Oklahoma v. Hamilton (2001), a man was treied for bludgeoning to death his wife. The murder defendant hired blood-spatter expert Tom Bevel to testify for the defense. But on cross-examination by the prosecution, Bevel stunned the courtroom with his conclusion that the blood spatter was consistent with the DEFENDANT having committed the murder. Blood-spatter evidence is an applied science, and Bevel--who was never "married to a theory"--applied the science to the facts and testified truthfully and objectively.

Anonymous said...

Why isn't forensics used more today? So many of the cases I've come across don't include it. Is it the cost?

Gritsforbreakfast said...

The fact that pseudoscience has been accepted in court and impacted thousands of cases has ZERO relationship to whether those theories are valid.

For that matter, people who attempt to analyze blood splatters for a living, I'm SURE, would disagree. So what? In the same vein, gypsy women who give palm readings on the side of the road for $10 a pop, I'm certain, would swear up and down their services are based on valid techniques. I don't believe them either.

Blood splatter evidence is not "applied science" when performed by "forensic serologists" because they've not been trained in the science that should be applied. They're biologists, not physicists - their training does not prepare them to analyze the evidence in the ways you suggest, whether their testimony helps the prosecution or the defense.

Finally, if the case you described was disproven by blood splatter evidence, it was an INCREDIBLY weak case to begin with.

Anonymous said...

Grits, it's blood SPATTER, not splatter.