Bloodstains Testing

Composition of Blood

• Plasma: Fluid component– Water (90%)– plasma proteins– Other solutes

• Formed elements: Cells and fragments– erythrocytes (red blood cells)– leucocytes (white blood cells) – Platelets

Bloodstains

• Wet blood has more value than dried blood because more tests can be run.

– Blood begins to dry after 3 – 5 minutes of exposure to air.

– As it dries, it changes color towards Brown or black.

Nature of Blood Evidence

• Blood/Bloodstains may be encountered as physical evidence in:

– Homicides– Sexual Assault– Vehicular hit-and-run– Burglary– Other crimes

"Every Contact Leaves a Trace".

Dr. Edmond Locard

Blood at the Scene is the most visible example of the Locard Exchange Principle

血痕检验的目的和要求

Is this stain blood?

Human blood?Animal blood ？

Whose blood?SuspectVictim

Process of Blood Testing

Visual inspection

Presumptive test

Confirmatory tests

Species-origin test

Individual Identification Paternity Testing

Location Color Shape Area

Visual inspection

Luminol

This chemical is used by crime scene investigators to locate traces of blood, even if it has been cleaned or removed.

Investigators spray a luminol solution is throughout the area under investigation and look for reactions with the iron present in blood, which causes a blue luminescence.

Luminol Reaction

How is blood evidence detected at a crime scene?

Luminol Testing

Luminol will give false reactions.

• One problem is that other substances also react, such as some metals, paints, cleaning products, and plant materials.

Luminol Testing

Studies have shown that luminol will cause the loss of several genetic markers.

– Another problem is that the chemical reaction can destroy other evidence in the crime scene.

Luminol Testing

Because Luminol is so sensitive to bloodstains, it is occasionally used to enhance bloody impressions (shoeprint, fingerprint, etc).

• Not the best method however, because it is water-based. This could cause loss of valuable information from a bloodstain.

First choice should be high intensity light.

Light SourceInvestigators will first examine the crime scene to look for areas that may contain blood.

They may use a high-intensity light or UV lights to help them find traces of blood as well as other bodily fluids that are not visible under normal lighting conditions.

How is blood evidence detected at a crime scene?

For small/movable item——collect the whole object

For big /immovable evidence ——scraping ， shearing ， cutting ， wet transferring ， tape Lifting

Label

Case file number

Description of the biological evidence(type, number, color ， location and so on)

The date and time of picking up the evidence

The place of picking up the evidence

The person who pick up the evidence——signature

Each item of evidence must be packaged separately and labeled with accurate tag

The characteristics of biological evidence from crime scenes

Biological evidence

The changement of the environment(high temperature 、 rain 、

strong sunlight 、 microbe degradation and so on)

denaturation 、 degradation 、 corruption

Correct collection 、 storage and test as soon as possible

How to store biological evidence

The storage of Biological evidenceBody fluid(blood, urine, saliva and so

on ）

Refrigeration(4℃or -20℃) or made stain

Air dried in shadow and

cool

Less than one week: 4 ℃

More than one week: 20 ℃

Presumptive test

Sensitive

Rapid

特异性低

Simple

Less amount

Blood – Presumptive testsBased on the peroxidase properties of hemoglobin

globin

heme

Common Presumptive Tests

phenolphthalin (Kastle-Meyer)leucomalachite green (LMG)Luminol (BlueStar)3,3’,5,5’-Tetramethylbenzidine (TMB)leucocrystal violet (LCV)o-tolidineBenzidine: Carcinogenico-toluidinehydrogen peroxide: Bubbles

Blood Reagent TestsThese tests, referred to as presumptive tests, are used to detect blood at crime scenes based upon the properties of hemoglobin in the blood. Further tests at the crime lab can determine if it is human blood or not.

Examples:

• Phenolphthalein is a chemical that is still utilized today and is usually referred to as the Kastle-Meyer test and produces a pink color when it reacts with hemoglobin.

•HemaStix is a strip that has been coated with tetramethylbenzidine (TMB) and will produce a green or blue-green color with the presence of hemoglobin.

Kastle-Meyer TestVideo

HemaStix

Blood – Presumptive testsGeneral Considerations

heme has peroxidase activity

2H2O2

2O· + 2H2O

Heme Fe+++

Oxygen free radicals

cleaved from peroxide group

Heme Fe++

Blood – Presumptive testsGeneral Considerations

Free radicals interact with organic chemicals (dyes)

O· chemical oxidized

Presumptive test detects oxidized organic dyes

+ Chemical reduced

Kastle-Meyer Test

RareSome substances inhibit reactionBlood can mask the color changeAcidic solutions can mask the reaction

false negatives

Benzidine

• • The benzidine test is used for many years but

has been discontinued because the reagent is carcinogenic.

Presumptive test

(-) Not blood or blood destroied

stop

(+)May be blood

GO

Confirmatory tests

Possible bloodstains Definite bloodstain

Specific

灵敏度低

Takayama test

操作简便、结晶清晰，但高山试剂久置易失效，每次试验时应当用已知血痕作阳性对照，且灵敏度低。

Confirmatory tests

(-)Not Blood（ Less or Destroied ）

stop

(+)Blood

GO

Species-origin test

Species-origin

Human Bloodstains

Animal BloodstainsBloodstains

加 样 区 反 应 区 吸 附 区

检测线抗人 Hb抗体

为 Ig

质控线抗 Ig抗体为抗 Ig

包被免疫胶体金的玻璃纤维

膜

硬质塑料底板

吸水滤纸

Human BloodCross-reaction with Ferret BloodAnti-human Hemoglobin

Human BloodCross-reaction with Ferret BloodAnti-human Hemoglobin

Species-origin test

(-)Animal (+)Human

Visual inspection

Presumptive test

（－）不是血（或已破坏）（＋）可能是血

Confirmatory tests

（－）不是血（量太少或已破坏） （＋）肯定是血

Species-origin test

Bloodstain Testing

（－）不是人血 （＋）是人血

Individual Identification Paternity Testing