Serology Flashcards
What is serology?
defined as the medical science of dealing with serums
What is serum?
Serum is the clear yellowish fluid obtained when whole blood is separated into its solid and liquid components
What is forensic serology?
- blood is analyzed to determine its source (at a crime scene or on an object)
- deals with: blood, semen, saliva, urine, feces
- often degraded or in stain form
What are the effects of sample degradation? (ie: what do the quality and condition of a sample stain affect?)
- the type of analysis that can be preformed
- whether analysis can be preformed at all
Evidence condition is key to its introduction to court, what can it be compromised by?
- break in the chain of custody
- degradation of sample due to inadequate storage
When examining dried blood what questions should you be prepared to anwser?
- is it blood?
- from what species did the blood originate?
- if the blood is of human origin, how closely can it be associated to a particular individual?
What is the proper scientific approach of examining blood? (5 steps)
- careful visual examination of the item or evidence to locate any stains or material visibly characteristic of blood
- application of suitable presumptive screening test
- application of a specific and sensitive test to confirm blood presence
- determination of biological species (animal or human) origin
- characterization of the blood using one or more genetic markers
What is blood made up of?
- cellular portion - 45%
- red blood cells
- white blood cells
- platelets - fluid portion - 55%
- plasma
- formed principally of water
What are platelets?
- smallest of the formed elements
- involved in clotting
What are erythrocytes?
- transport oxygen and carbon dioxide throughout the body via the circulatory system
- accomplished by hemoglobin
- do not contain nuclei
What are leukocytes?
- active in the immune system
- neutrophils - the most common white blood cell, is important in the removal of bacteria and parasites from the body
How do you identify is a body fluid is blood, semen or saliva?
- visual examination
- presumptive testing is
highly sensitive but not specific for a particular substance - confirmatory testing yields positive results for the substance in question and only that substance
What is visual examination for blood?
- looking for reddish brown staining on items
- can use an alternate light source to locate blood on dark items (blood will absorb the light and appear darker than surrounding material)
What do presumptive tests for blood do?
tests for blood to react with the hemoglobin present in the blood
Whats the most common presumptive test?
catalytic colour
What substances can interfere with a presumptive blood test?
- enzymes
- oxidizing chemicals and metals - like copper and iron
How are presumptive tests done if area is large?
chemicals like luminol or fluorescein are sprayed onto the surface and visualized with an alternate light source
What is the oldest chemical confirmatory test for blood?
- using the formation of specific crystals
What is the Takayama confirmatory test?
- ferrous iron from the hemoglobin reacts to produce red feathery crystals
What is the Teichmann test?
- mixture of chemicals heated to react to hemoglobin
- converts hemoglobin to hemin which creates brownish-yellow rhomboid crystals
What are antigens?
- any substance which provokes an adaptive immune response
- located on the surface of red blood cells and are responsible for blood type characteristics
What is the ABO blood grouping system?
- A, B, O, refer to antigens on the surface of the red blood cells
- corresponding antibodies - anti-A and anti-B exist in plasma
What happens if blood of different types are mixed?
- blood will agglutinate or clump together
Is blood typing still conducted in forensic labs?
no
How do you determine a species with blood?
- serum protein analysis
Why do forensic labs often test for semen?
crimes that involve sexual offences and require testing for the presence of semen
How do you visually examine for semen?
- white yellowish staining
- can use alternate light source and goggles to visualize
What is the most definitive test for visually identifying semen?
microscopic identification
What is the most common presumptive test for semen?
- acid phosphate test
- positive indicated by purple
What is a microscopic confirmatory test for semen?
- Christmas tree stain
- stains head read and tail green
What is a chemical confirmatory test for semen?
- test for p30, a prostate specific antigen
- similar to blood test
What evidence is collected from medical examination of a sexual assault victim?
- Pubic Combings
◦ Pubic Hair Controls (15-20)
◦ External Genital Swabs
◦ Vaginal Swabs
◦ Cervix Swabs
◦ Rectal Swab
◦ Swabs of body areas - Oral Swabs
- Head hairs (25)
- Blood Sample
- Buccal Swab
- Fingernail Scrapings
- Urine Specimen
- All Clothing
How long do seminal constituents persist in the vagina?
- motile sperm: 4-6 hours
- non-motile sperm: 3-6 days
- seminal acid phosphatase: less than 48 hours
- prostate specific antigen: less than 72 hours
What evidence situations can saliva be used in?
- bite marks, licked adhesive, eating and drinking surfaces, expectoration
- detection may be difficult
How can you visualize saliva?
- can be visualized with an alternate light source
- saliva will fluoresce
How do you pack biological evidence?
- before the collection of biological evidence begins, it is important that it be photographed and recorded on sketches
- wearing disposable latex gloves while handling evidence is required
- the packing of biological evidence in airtight or plastic containers must be avoided because the accumulation of residual moisture could contribute to the growth of DNA-destroying bacteria or fungi
- each stained article should be packaged separately in a paper bag or well ventilated box
- all biological evidence should be refrigerated or stored in a cool location until delivery to the lab
