Chapter 8 Forensic Serology

Forensic Serology Introduction

• 1901, Karl Landsteiner found blood to be distinguishable by group– Led to the classification of the

ABO system• By 1937, the Rh factor was

demonstrated– Numerous other blood

factors/groups discovered– More than 100 different blood

factors known to exist

Forensic Serology Introduction• For the most part, no

two individuals have the same combination of blood factors

• Blood factors are controlled by genetics; therefore, they are highly distinctive

• DNA has become the favored method of identifying individual through blood

The Nature of BloodAntigens and Antibodies

• Blood is a complex mixture of cells, enzymes, proteins, and inorganic substances– Plasma – the fluid portion composed

mostly of water and makes up 55% of blood content

– Cells - red blood cells (erythrocytes), white blood (leukocytes), & platelets are suspended in plasma and accounts for 45% of blood content

• Blood clots occur when a protein, fibrin, traps RBCs; the liquid that separates from blood when a clot is formed is the blood serum

Antigens and Antibodies

• Red Blood Cells– Transport oxygen from

lungs to body tissue and then carbon dioxide from tissue to lungs

– Antigens are present on the surface of the RBCs

– Antigens impart blood-type characteristics to the red blood cells

Antigens

• A type A individual has A antigens on the surface the of the RBCs

• A type B individual has B antigens on the surface the of the RBCs

• A type AB individual has both A and B antigens on the surface the of the RBCs

• A type O individual has neither A or antigens on the surface the of the RBCs

• A type Rh positive individual has the Rh factor or D antigen

Antigens and Antibodies

It is the presence or absence of the three antigens – A, B, or D – that determine the

compatibility of a blood donor and recipient.

The fundamental principle of blood typing is that for every antigen, there

exists a specific antibody.

Antibodies• Antibody – a protein that destroys or inactivates

a specific antigen; antibodies are found in the blood serum

• The blood serum which contain antibodies is antiserum

• For every antigen, there is a specific antibody,– Anti-A is the antibody specific to antigen A– Anti-B is the antibody specific to antigen B– Anti-D is the antibody specific to antigen D

Antigens and Antibodies in Normal Blood

Blood Type Antigens in RBC Antibodies in

Serum

A A Anti-B

B B Anti-A

AB AB Neither anti-A or anti-B

O Neither A nor B Both anti-A and anti-B

Agglutination

• An antibody will react only with its specific antigen– If serum containing anti-B is

added to RBCs carrying the B antigen, the two will combine

– Antibodies are typically bivalent – they have two reaction sites and can attach to two antigens on different RBCs

• The clumping together of RBCs by the attachment of antibodies is called agglutination

Agglutination

Blood TypingSerology refers to a broad scope of laboratory tests that use specific antigen and serum antibodies reactions

Blood typing 1. Test blood with anti-A

and anti-B serum2. Test for the presence of

antibodies, anti-A or anti-B, with known antigens

Identification of Blood with Known Antiserum

Anti-A Serum + Blood

Anti-B Serum + Blood

Antigen Present Blood Type

Agglutination No Agglutination A A

No Agglutination Agglutination B B

Agglutination Agglutination A and B AB

No Agglutination

No Agglutination

Neither A nor B

O

Identification of Blood with Known Cells

A Cells + Blood

B Cells + Blood

Antibody Present Blood Type

Agglutination No Agglutination Anti-A B

No Agglutination Agglutination Anti-B A

Agglutination Agglutination Both Anti-A & Anti-B O

No Agglutination

No Agglutination

Neither Anti-A nor

Anti-BAB

If your blood type is . . .

TypeYou Can Give Blood To

You Can Receive Blood From

A+ A+  AB+ A+  A-  O+  O-

O+ O+  A+  B+  AB+ O+  O-

B+ B+  AB+ B+  B-  O+  O-

AB+ AB+ Everyone

A- A+  A-  AB+  AB- A-  O-

O- Everyone O-

B- B+  B-  AB+  AB- B-  O-

AB- AB+  AB- AB-  A-  B-  O-

Out of 100 donors . . . . .

84 donors are RH+

16 donors are RH-

38 are O+ 7 are O-

34 are A+ 6 are A- 9 are B+ 2 are B-

3 are AB+ 1 is AB-

Despite how well the crime scene may get cleaned up, even the finest trace of blood can often be detected and further tested. It is often the case that while the perpetrator may scrub down the obvious places, he can still miss between floorboards, under pipes, and inside drains. Merely by pouring water on some tiles at a murder scene and pulling them up wherever the water flowed beneath them, one detective found the only existing trace of the crime--blood. His discovery so surprised the killer, who felt certain he'd done a through job of cleaning up, that he instantly confessed.

Forensic Blood Test

Forensic Blood Test

Forensic Scientist must answer the following questions when examining dried blood:

1. Is it blood? 2. From what species did the

blood originate?3. If the blood is human, how

closely can it be associated with a particular individual?

Forensic Blood Tests

• Color Tests• Luminol

• Precipitin• Gel Diffusion

Color Tests

• Phenolphthalein indicator (Kastle-Meyer color test)– When mixed with blood and hydrogen

perioxide, the hemoglobin will turn pink

http://www.youtube.com/watch?v=6Ex0Fd_PDhUhttp://www.youtube.com/watch?v=pnH2HnB-GrI

Luminol Test• When in contact with

blood, produces light• Highly sensitive – can

detect bloodstains diluted up to 300,000 times

• Used to spray large areas such as carpets, walls, flooring, or interior of a vehicle

• Will not interfere with DNA testing CSI Miami Demo (Note – DNA can

be tested with PCR techniques with diluted samples)

Microcrystalline Tests

Precipitin

• Used to determine if blood is of human origin

• Animals will produce antibodies when injected with human blood; these antibodies, called human serum, can be isolated

Precipitin

Layer a sample of the bloodstain in a small test tube with a layer of human antiserum on bottom.

The human blood will react with the antiserum forming a cloudy band in the test tube.

Human Blood

Animal Antiserum

Gel Diffusion• Another type of precipitant test• Extracted bloodstains and human anti-serum are placed

in separate openings on opposite sides of a gel. • Antigens and antibodies induced to move towards each

other when an electrical charge is applied. • A specific line is formed if the antigen and antibodies

react together.

Human BloodAnimal Antiserum

Precipitin

• Very sensitive tests requiring a small amount of blood

• Human bloodstains can be dried for as long as 10 to 15 years

• Diluted bloodstains can also give positive results

• http://www.youtube.com/watch?v=gK1s3FCkOm8 • The location, distribution, and appearance of

bloodstains and spatters may be useful for interpreting and reconstructing the events that must have occurred to have produced the bleeding.

• The significance of the position and shape of blood patterns with respect to their origin and trajectory is exceedingly complex and requires an experienced examiner

• An analysis usually requires controlled experiments creating an environment comparable to the crime scene.

Stain Patterns of BloodHerbert L. MacDonell’s

observation’s:1. Surface texture is

important in the interpretation of blood stain patterns and correlations between standards and unknowns are valid only if identical surfaces are used. In general, the harder and less porous the surface, the less splatter results.

Stain Patterns of Blood

2. The direction of travel of blood striking an object may be discerned by the stain’s shape. The pointed end of a bloodstain always faces its direction of travel.

Stain Patterns of Blood3. It is possible to determine the impact angle of blood

on a flat surface by measuring the degree of circular distortion of the stain. A drop of blood striking a surface at right angles gives rise to a nearly circular stain; as the angle decreased, the stain becomes elongated in shape.

Stain Patterns of Blood4. The origin of a blood

spatter in a two-dimensional configuration can be established by drawing straight lines through the long axis of several individual bloodstains. The intersection or area of convergence of the lines represents the area from which the blood emanated.

Stain Patterns of Blood Resources

• http://projects.nfstc.org/gallery/main.php?g2_itemId=3857

• http://www.crimescene-forensics.com/Blood_Stains.html

• http://www.videojug.com/interview/csi-and-blood-evidence-2#why-are-blood-stains-studied-in-csi