Blood and Other Bodily Fluids

• Author: D. P. Lyle
• Pages: 159-177

Blood and Other Bodily Fluids 159

CHAPTER 10

BLOOD AND OTHER

BODILY FLUIDS

Serology is the analysis of blood and other bodily fluids, such as semen,

saliva, and tears. Si nce many crimes, from assaults to homicides, result

in the spillage of blood, blood is the most common biological fluid left at a

crime scene. It is also the most useful since it offers the forensic team sev-

eral inves tigative avenues , some of which d epend on blood’s physica l prop-

erties (how it behaves as a liquid), while others depend upon its chemical

and biological behaviors.

We delve into the physical properties of blood in Chapter 14, where we

will see how blood spatter analysis is used to reconstr uct crime scenes,

determine the sequence of events surrounding the crime, and follow the

actions of the perpetrator, the victim, and often the witnesses. In this chap-

ter we will look at the work of the forensic serologist, who comes in after

the blood spatter analysis is completed to conduct chemical and biological

tests of any crime scene or suspect blood samples.

It is worth noting that since the advent of DNA testing (Chapter 11),

the serological evaluation of blood and other bodily fluids has dimin-

ished as a forensics tool. Simply put, DNA testing offers much greater

160 Blood and Other Bodily Fluids

individualization than does serology, yet serology remains a useful tool for

the forensic scientist.

The Characteristics of Blood

Blood is a complex substance. Its liquid portion, called plasma, contains

proteins, enzymes, clotting factors, and electrolytes, as well as three basic

types of cells: leucocytes (white blood cells, or WBCs), erythrocytes (red

blood cells, or R BCs), and platelets (tiny cells involved in blood clotting). If

whole blood is allowed to clot and the clot is removed, the yellowish liquid

remaining is called serum. It contains most of the proteins and enzymes of

plasma, but none of the cells or clotting factors, which have been consumed

by the clotting process.

For years, blood transfusions from one person to another weren’t pos-

sible. Too often the blood would clot within the recipient’s veins and death

wasn’t uncommon. Then, in 1901, Karl Landsteiner made one of the most

important discoveries in medical hist ory when he observed that this trans-

fusion reaction wasn’t universal. Sometimes it would occur and at other

times it wouldn’t. His extensive research into this phenomenon led to his

discovery that human blood could be classif ied into 4 types, which he des-

ignated A, B, A B, and O. Landsteiner called his classif ication scheme the

ABO system.

He showed that if a person received blood from a donor with the same

type of blood, he was much less likely to have a reaction than if he received

blood from a donor of a different type. Landsteiner’s ABO system is still in

use today and serves not only as the basis for all blood transfusions but also

for matching blood samples in the forensic lab.

The ABO System

From a forensic point of view, the two most important components of blood

are the RBCs and the serum, since these alone can deter mine the ABO

type of a blood sample or bloodstain. On the surface of the RBCs, the cells

that transport oxygen from the lungs to the tissues, are molecules called

antigens, and it is these antigens that determine the blood type. There

are only two types of antigens, designated either A or B. Type A blood has

only A antigens on its RBCs, type B only B antigens, type A B both A and B

antigens, and type O neither antigen.