blood

• The Plan!


  • Blood Cells
  • Methods in Detecting Blood
  • Post-Mortem Toxicology of Blood
  • Saliva and Semen
  • Vitreous Humour
  • Urine and Faeces
• Blood cells


  • Study of blood cells = Haematology
  • Study of serum = Serology
• Types of blood cells

  • With nucleus
  • Without nucleus
• Red Blood Cells (RBC/erythrocytes)


  • Pigment haemoglobin
  • Transportation of O2 and CO2
• Platelets


  • Star shaped
  • Clotting mechanism
  • Maintain integrity of blood vessels
• White Blood Cells (WBC/leucocytes)


  • Many different types
  • Responsible for immune defence
  • Contain both DNA and mtDNA
• Plasma


  • 55% of blood
  • 2.7-3L per adult
  • 90% H20 + 8% plasma proteins + minerals, antibodies, hormones, enzymes
• Serum


  Blood plasma – protein content
• Antigens


  • Molecules on the outer surface of the cell
  • Recognized by Antibodies
• If antigens do not match, it will be destroyed by the WBC. This is known as immune response.
• ABO blood type system


  • RBC may only contain A antigen (Type A)
  • RBC may only contain B antigen (Type B)
  • RBC may only contain A and B antigen (Type AB)
  • RBC may only contain neither A or B (Type O)
  • Antibody in Plasma: Anti-B, Anti-A, Neither anti-A or anti-B, Both anti-A and anti-B
• Rhesus (Rh) blood group

  • Aka antigen-D and agglutinogen
  • Comes in both + and - forms
  • 83% of the UK population are Rh(+)
  • Most belong to either blood types O (44%) or A (42%)
  • Type AB more common in Japan (10%) than UK (4%)
• Methods in Detecting Blood

  1. Bloodstains not always obvious

  2. Latent blood can be detected using an indicator substance

  3. Haemoglobin reaction

  4. Presumptive test
• Luminol


  • Most effective presumptive test
  • Run high risk of degradation/diluting
  • Mix Luminol, Sodium Carbonate, Sodium perborate/hydrogen peroxide
• Kastle-Meyer Test


  • Not as sensitive as Luminol
  • Must not be done directly on stains
  • Interferes with DNA extraction
  • Colour change is immediate, turns from colourless to pink
• Titanium dioxide


  • Sprayed onto suspect area
  • If blood is present turns white
  • Good for detection on dark surfaces
  • Flammable
  • Poisonous
  • Residue compromises further analysis
• Infrared Imaging/ Hyperspectral Imaging


  • Potential chemical free detection of latent blood-stains
  • Can be used to detect blood underneath layers of paint
• Methods in Confirming Blood


  1. Precipitin test

  2. PCR based protocol using primers for human mitochondrial cytochrome b gene
• Post-Mortem Toxicology of Blood


  • Difficult because the blood has stopped flowing
  • Drugs become redistributed
  • Concentrations alter
• Saliva


  • Slightly alkaline
  • Detection of salivary amylase using ELISA
  • Traces can be left via bite marks
  • Possible to isolate DNA and some drugs
• Semen


  • Gelatinous fluid
  • Typical ejaculation 1.5-5ml
  • Approx. contains 40-250 million spermatozoa
  • Can be released after death due to rigor mortis in the dartos muscle in the scrotum
• Forensic Indicators for Saliva and Semen

  • Serological or DNA analysis
  • Prostatic Acid Phosphatase test
  • Christmas Tree Stain
  • RSID – Semen Strip test
• Split preferential extraction


  1. Sperm can be separated from other cells on the basis of a preferential 'lysis' technique

  2. Epithelial cells can be separated from the sperm remain intact (mainly sexual assaults)
• Vitreous Humour


  • Clear gelatinous matrix located behind the lens within the vitreous chamber
  • Rise in K following death
  • PMI calculation using linear regression analysis
• Faeces


  • Can indicate diet, health, and contain DNA
  • Difficult to extract DNA due to bile salts
• Urine


  • Does not contain a lot of cells
  • Easier to obtain (nuclear) DNA profiles of women
  • Shed more epithelial cells than men
  • Can indicate dehydration, medication, health conditions
• Overview of Forensic Information from Bodily Fluids/Biological Samples

  • Blood (serology): Blood Typing, Rhesus Factor, Enzyme Polymorphisms
  • Blood (molecular): DNA Profiling
  • Blood (chemistry): Poisoning, Drug Use
  • Bloodstains: Sequence of events, BPA, DNA Profiling
  • Saliva and Semen: ID, Link to victim/location
  • Faeces and Urine: ID, Link to victim/location, Diet, Drug Use
• What is 'accuracy' in the context of analytical measurement?

  In analytical measurement, 'accuracy' refers to how close a measured value is to the true or accepted reference value. It indicates the correctness of a measurement.
• What is 'accuracy' in the context of analytical measurement?

  In analytical measurement, 'accuracy' refers to how close a measured value is to the true or accepted reference value. It indicates the correctness of a measurement.
• What is 'precision' in the context of analytical measurement?


  In analytical measurement, 'precision' describes the repeatability or consistency of measurements when repeated under unchanged conditions. It indicates the reproducibility of results.
• Can a method be precise without being accurate?

  Yes, a method can be precise without being accurate if it consistently produces similar results that are not close to the true value.
• Why are both accuracy and precision critical in analytical measurement?

  Both accuracy and precision are critical for reliable analytical results because accuracy ensures the correctness of the measurement, while precision ensures the consistency and reproducibility of the results.
• What challenges are there in detecting bloodstains at a crime scene?

  Bloodstains are not always obvious and can include small blood drops. Cleaning a crime scene often leaves behind traces that are difficult to remove entirely.
• How can 'latent' blood be detected?
• Latent' blood can be detected using an indicator substance that reacts with haemoglobin, causing a colour change which reveals the presence of blood.


  luminol
• How sensitive are the tests for detecting blood, and what are their limitations?

  The tests for detecting blood can be very sensitive. A positive reaction indicates the presence of haem, classifying the test as presumptive. However, these tests can suffer from interference from common environmental chemicals.
• Why are controls important in blood detection tests?

  Performing a negative control, such as a spot of distilled water, and a positive control, such as a spot of dried animal blood, is important to validate the results of the tests and to ensure reliability.
• What is Luminol and how is it used in blood detection?

  Luminol, first used in 1937, remains one of the most effective presumptive tests for detecting blood. It involves a mixture of Luminol (5-amino-2,3-dihydro-1,4-phthalazinedione), sodium carbonate, and sodium perborate or hydrogen peroxide. Luminol is sprayed on the area after sample collection, causing blood traces to luminesce. However, using Luminol runs the risk of degrading or diluting the sample, so it is essential to sample first before spraying.
• What are the characteristics and limitations of the Kastle-Meyer test for blood detection?

  The Kastle-Meyer test is not as sensitive as Luminol and must not be done directly on stains because it interferes with DNA extraction. However, it is quick, simple, and cheap, with an immediate colour change from colourless to pink.
• Why is the Kastle-Meyer test used despite its limitations?

  Despite its limitations, the Kastle-Meyer test is used because it is a quick, simple, and inexpensive method for detecting blood, providing immediate results with a visible colour change from colourless to pink.