Examination of Blood in Forensics

By @forensicfield

INTRODUCTION

Blood is a type of biological evidence which is commonly found at the scene of crime.

Blood stains are often found at various types of crime scene, such as homicide, hit and run, assault, child abuse, rape, robbery and burglary. it also uses for DNA extraction and establishes  the paternity test.

Since the discovery of the ABO system by Land-steiner in 1900, knowledge in human blood identification has expanded tremendously.

Composition Of Human Blood

Blood is a mixture of many components:

* Cells

* Enzymes

* Proteins                            

* Water

* Inorganic substances (salts)

Blood contains 2 types of proteins which are-

  • Plasma
  • Corpuscles

The blood cells are of three main types:

  • Red Blood Cells (Erythrocytes)
  • White blood cells (Leucocytes)
  • Platelets (Thrombocytes)

Use of Blood detection in Forensic Science:

Blood is one of the most important biological traces that are often found on the crime scene. Due to valuable information it contains, it is considered to be a very important forensic tool. Analysis of different aspects of bloodstains can contribute to clarify the circumstances under which some violent crimes have been committed. Such crucial information can point criminal investigation in the right direction and help solve the crime. In some cases it can also help with legal determination of criminal offense which can lead to more accurate and more appropriate punishment for the perpetrator. It is very important to determine the sequence of events during the commitment of a violent crime involving blood.

Identification Of Source Of Blood

Foetal blood–  presence of HbF or Alpha Protein.

Blood of Pregnancy and abortion – Chorionic Gonadotropins or or Alkaline Phosphatase.

Menstrual blood– Fibrin Content, endometrial tissues.

Venous blood– dark in color, oozes gradually and no spurting.

Arterial – bright red and copious and showed spraying.

Methods For The Identification Of Blood

5 Types Of Blood Test Or Methods Occurred-

  1. Visual / Physical examination
  2. Microscopic examination
  3. Chemical Examination
  4. Spectroscopic Examination
  5. Serological examination
Visual /  Physical Examination

The search for the presence of blood at a crime scene is normally done by close visual examination.  The possibility exists, however, that blood may be present in amounts too little to see with the unaided eye, or that the blood at the scene had been “cleaned up” prior to arrival of the crime scene team. 

Fresh stains – bright in colour, turns to brown and black after some time. Fresh stains soluble in water or in saline

Ante-mortem blood Stains – Removed in scales due to presence of fibrin.

Post-mortem blood stain – changes in powdered on removal.

Microscopic Examination

Fresh blood stain in Microscope  – Erythrocytes and leukocytes.

Microscopic appearance of cells found in a stain extract may reveal other information.

If blood stains in an environment with a higher solute concentrate, water leaves the cell by osmosis and the cells shrink and change shape.

If stains are fresh it is possible to reconstitute the stain and proceed with microscopical identification of cellular components.

Chemical Examination

Preliminary

  1. BENZIDINE TEST
  2. LUMINOL TEST
  3. PHENOLPHTHALEIN (KASTLE – MAYER TEST)
  4. FLUORESCEIN TEST
  5. LEUCOMALACHITE GREEN TEST
  6. COLORIMETRI TEST

Confirmatory

  1. TEICHMANN TEST
  2. TAKAYAMA TEST
  3. WAGENNAR TEST
  4. SPECTROPHOTOMETRY TEST
  5. ELECTROPHORESIS TEST

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