Forensic Serology Basics

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Questions and Answers

What is the primary purpose of serology in forensic science?

To identify cell types on items or the type of stain present.

Differentiate between presumptive and confirmatory tests in serology.

Presumptive tests indicate a possible origin of the stain but do not conclusively prove it, while confirmatory tests conclusively determine the stain's origin.

What are two common types of false results in serological testing?

False positive and false negative.

List three body fluids that are commonly tested in serology.

Blood, semen, and saliva. Signup and view all the answers

What components make up blood?

Blood consists of plasma, red blood cells (erythrocytes), white blood cells (leucocytes), and platelets. Signup and view all the answers

What is the composition of plasma in blood?

Plasma is 90% water and 10% proteins, minerals, hormones, and antibodies. Signup and view all the answers

What role does hemoglobin play in red blood cells?

Hemoglobin transports oxygen to cells and carbon dioxide to the lungs. Signup and view all the answers

What does a positive presumptive test indicate regarding blood evidence?

It indicates that the evidence may be blood. Signup and view all the answers

What does a pink color at the stage of adding KM reagent indicate?

A pink color indicates a false positive result, requiring the test to be restarted. Signup and view all the answers

What is the main chemical reaction involved in the chemiluminescence assay for blood identification?

Luminol is oxidized by heme to produce chemiluminescent light. Signup and view all the answers

What is one significant advantage of using Blue Star in blood detection?

Blue Star does not require 100% darkness for detection. Signup and view all the answers

What does the immunochromatographic assay specifically detect?

It detects human glycophorin A (GPA), a protein present on human red blood cells. Signup and view all the answers

Explain the role of antibodies in the immunochromatographic assay.

Antibodies are used to detect human antigens, allowing for species confirmation of blood. Signup and view all the answers

What are the primary roles of white blood cells in the body?

They defend the body against infection and are responsible for providing DNA in blood. Signup and view all the answers

What limitation is shared by both the KM reagent and luminol in blood detection?

Both can produce false positives and false negatives. Signup and view all the answers

Describe the visual characteristics of blood when it dries on a smooth surface.

Dried blood appears flaky and cracks when on a smooth surface. Signup and view all the answers

What is a downside of using the chemiluminescence assay in terms of DNA analysis?

The assay can dilute blood, leading to lower levels of DNA for analysis. Signup and view all the answers

How does the room condition affect the visibility of the chemiluminescent reaction?

The room must be completely dark to see the light emitted by the reaction. Signup and view all the answers

What is the significance of a pink result in the Kastle-Meyer Test?

A pink result indicates a presumptive positive for the presence of blood. Signup and view all the answers

Why is the Kastle-Meyer Test not specific for blood?

The test can yield false positives due to the presence of heme in substances other than blood, like oxidants and plant peroxidases. Signup and view all the answers

What is the role of heme in the colorimetric assay for blood identification?

Heme acts as a catalyst for the oxidation-reduction reaction in the assay. Signup and view all the answers

Identify one potential source of false negatives in blood testing.

Reductants can inhibit the oxidation reaction, leading to false negatives. Signup and view all the answers

How sensitive is the Kastle-Meyer Test in detecting blood?

It is very sensitive, capable of detecting down to a 10^-5 fold dilution. Signup and view all the answers

What color does the reductant phenolphthalin turn to in the presence of heme and peroxide?

It turns pink when oxidized by heme in the reaction. Signup and view all the answers

What are the three main components of spermatozoa?

The three main components of spermatozoa are the head, middle piece, and tail. Signup and view all the answers

What is the function of the acrosomal cap in spermatozoa?

The acrosomal cap contains enzymes that break down the outer layer of the egg for fertilization. Signup and view all the answers

How does the middle piece of spermatozoa contribute to its mobility?

The middle piece contains mitochondria, which provide energy to power the tail. Signup and view all the answers

What are the steps involved in preparing a microscope slide for sperm identification using microscopy?

Cells are transferred to a slide with water, heat-fixed, and then stained with a Christmas tree stain. Signup and view all the answers

What do the red and green dyes in the Christmas tree stain indicate when identifying sperm?

The red dye stains all nuclei and acrosomal caps, while the green dye stains the sperm neck, tail, and all cell membranes. Signup and view all the answers

What is the primary component of saliva, and what percentage does it represent?

Saliva is mostly composed of water, which makes up approximately 99% of its content. Signup and view all the answers

What role does the enzyme amylase play in saliva?

Amylase begins to break down food in the mouth by cleaving polysaccharides. Signup and view all the answers

What types of amylase are found in humans and where are they produced?

Humans have pancreatic α-amylase produced by the pancreas and salivary α-amylase produced by the salivary glands. Signup and view all the answers

Describe the purpose of an immunochromatographic assay in saliva identification.

An immunochromatographic assay tests for human α-amylase to identify saliva. Signup and view all the answers

What is the significance of using a wavelength of 470-555 nm in visual examination of saliva stains?

This wavelength allows for visualization of light fluorescence in saliva stains. Signup and view all the answers

What is the significance of the minimum concentration in confirmatory testing?

It ensures that a positive result is reliable and accurately reflects the presence of a substance. Signup and view all the answers

What role does the anti-amylase antibody play in the immunochromatographic assay?

It binds to α-amylase, forming a complex that allows for the detection of saliva. Signup and view all the answers

Why is it important for all employees to follow the same Standard Operating Procedures (SOP)?

Consistency in following SOP ensures reliability and accuracy in testing processes. Signup and view all the answers

What must be done if there are deviations from the SOP?

Deviations must be documented and approved by the lab supervisor prior to use. Signup and view all the answers

How can improper validation of methods affect lab operations?

Improper validation can halt lab work until the method is correctly validated and approved. Signup and view all the answers

What type of microscope is primarily used for initial observations in forensics?

The stereomicroscope is used for initial observations due to its 3D visualization capabilities. Signup and view all the answers

What can happen to a forensic expert’s credibility if SOPs are not properly followed?

It can lead to perceptions of incompetence, making the expert appear unreliable and untrustworthy. Signup and view all the answers

Why must each testing method have its own SOP?

Each testing method has unique procedures that need to be clearly outlined for effective execution. Signup and view all the answers

What is the purpose of adding universal buffer in the immunochromatographic assay for blood identification?

To stabilize the sample and promote optimal binding of antibodies during the testing process. Signup and view all the answers

Explain the significance of the control line in the immunochromatographic assay.

The control line validates that the test was performed correctly and that the reagents are functional. Signup and view all the answers

What does the appearance of a pink line at the test line indicate?

It indicates the presence of human blood in the sample. Signup and view all the answers

Describe a limitation of reading results in the immunochromatographic assay before the 10 minute mark.

Results read before the 10-minute mark can be unreliable and may not indicate true positive results. Signup and view all the answers

What are the main components of normal semen?

Normal semen consists of seminal fluid and sperm cells. Signup and view all the answers

How does a vasectomy affect sperm production?

A vasectomy prevents sperm from reaching the reproductive tract but does not affect sperm production. Signup and view all the answers

What enzyme hydrolyzes α-naphthyl phosphate in the colorimetric assay for semen identification?

Acid phosphatase (AP) is the enzyme that hydrolyzes α-naphthyl phosphate. Signup and view all the answers

What visual characteristics assist in identifying semen stains using ALS/FLS?

Flavins and choline-conjugated proteins fluoresce under ultraviolet light, causing the stains to appear blue or yellow. Signup and view all the answers

What can a high concentration of antigens in the immunochromatographic assay lead to?

It can cause a high-dose hook effect, resulting in decreased intensity at the test line and potential false negatives. Signup and view all the answers

Why is the half-life of prostate-specific antigen (PSA) significant in semen identification?

The half-life determines how long PSA can be detected in dried stains, impacting the interpretation of results. Signup and view all the answers

What is a potential issue with identifying blood from diluted samples in the immunochromatographic assay?

The test line can be very faint or difficult to distinguish, leading to potential false negatives. Signup and view all the answers

How does the colorimetric assay help in mapping large items for semen evidence?

It allows the identification of purple areas corresponding to semen, which can be traced back to their original location. Signup and view all the answers

What components make up the seminal fluid produced from the prostate?

The prostate contributes acid phosphatase, prostate-specific antigen, citric acid, minerals, and enzymes. Signup and view all the answers

In the context of semen analysis, what does oligospermia refer to?

Oligospermia refers to a condition where men have an abnormally low sperm count. Signup and view all the answers

Study Notes

Fundamentals of Serology & Microscopy

The study of bodily fluids in forensic science.
Includes forensic investigation of fluids like vaginal secretions, semen, sweat, and blood.

Serology

Purpose: Identifying cell types and/or stains on an item.
DNA Analysis Support: Assisting in determining the best DNA analysis route, including identifying expected DNA amount and sex.
Procedures: Methods used in serology are not detailed in the provided excerpt.

Two Classifications of Tests

Presumptive Tests: Preliminary tests that indicate the origin of a stain. They don't definitively prove the nature of the stain. Useful for screening.
- Pros: Screens large items efficiently.
- Cons: High risk of false positives, not conclusive.
Confirmatory Tests: Tests that conclusively identify the origin of a stain. Often involve multiple procedures.
- Pros: Reduced risk of false positives, conclusive.
- Cons: More expensive, complex, and time-consuming.

False Results

False Positive: A positive result when the actual result should be negative. Example: Pregnancy tests.
False Negative: A negative result, when the actual result should be positive

Fluids Tested in Serology

Body Fluids: Blood, semen, saliva, urine, feces, menstrual fluid
Other Body Fluids: Cerebrospinal fluid, amniotic fluid, pleural fluid, vaginal secretions, and tissues.

General Classifications of Tests

Visual Examinations: Using naked eye, alternative lighting.
Colorimetric Assays: Chemical reactions cause color changes.
Chemiluminescent Assays: Chemical reactions cause light emission.
Immunochromatographic Assays: Employing antibodies to detect specific antigens.

Blood

Serology Test Results: Positive presumptive test (evidence may be blood), confirmatory test (evidence is blood).
Composition: Plasma, red blood cells (erythrocytes), white blood cells (leukocytes), platelets.
Weight Percentage: 8% of total body weight.
Blood Components: Plasma (fluid), red blood cells (oxygen transportation), white blood cells (immunity), platelets (blood clotting).
Red Blood Cell Makeup: No nucleus. Has hemoglobin protein, responsible for carrying oxygen around the body.

Hemoglobin

Haemoglobin's structure is based on iron-containing heme molecules in protein subunits. The molecules are contained in red blood cells, responsible for getting oxygen around the body.

White Blood Cells

Immunity: Defend the body against infection
DNA Source: Responsible for the DNA source in blood samples.

Platelets

Blood Clotting: Aid in blood clotting.
Vascular Injury Response: Collect in areas of vascular injury.
Nucleus Lack: No nucleus.

Workflow for Blood Testing

Includes steps for identifying the presence of blood, species identification, DNA profiling (human identification), and sample individualization. The order of the tests is not necessarily consecutive.

Identification of Blood: Visual Examination

Color: Appearance (candy-apple red, dark red).
Dry State On a Surface: Flaky or crack formation.
Light: Appears black under alternative light sources (ALS).

Identification of Blood: Colorimetric Assay

Kastle-Meyer Test: Oxidation-reduction reaction catalyzed by heme.
Phenolphthalin: Colorless reductant that turns pink when oxidized. Oxidized by heme and peroxide.
Hemoglobin: The catalyst for the reaction.
Positives: Pink color indicates a positive result for the presence of blood.
Sensitivity: Detects blood dilutions down to 10-5.
Not Specific: Can give false positives with household cleaning products.
False Negatives: False negative results can also happen if the sample is too dilute, or if a reductant is present.
Testing Procedure: Details how to test.

Identification of Blood: Chemiluminescence Assay

Luminol: Oxidized by heme, producing light.
Visualization: Useful for large areas, detecting small amounts of blood.
Sensitivity: Detects dilutions down to 10-3.
Dark Environment: Required for optimal visualization.
False Results: Potential for false positives.

Immunochromatographic Assay

Confirmatory Test: Analyzes for blood, and the species (human).
Process: Uses antibodies to detect human antigens. Mobilized anti-GPA antibody binds to GPA and creates a complex, while the unbound anti-GPA antibody binds to control immobilized antibodies.
Interpretation: Positive tests show a pink line at the test line, if there is a secondary pink line in the control line.
Sensitivity: Very sensitive, detecting low blood levels (10-14).
Factors: High concentrations of antigen can cause a false-negative "high-dose hook effect."

Semen

Composition: Contains seminal fluid, sperm cells, and many other components.
Typical Ejaculate: 2-5 mL, containing 10^7-10^8 spermatozoa/mL.
Sperm Production/Maturity: Produced in testes, mature in epididymus (3 months).

Semen: Acid Phosphatase (AP)

Prostate Source: Primary source in the body.
Lysosomes: Also found within lysosomes and other tissues.
Presumptive Test: AP presence is presumptive because it's found in other tissues.
Vasectomy Impact: Does not affect levels
Stability: Half-life of 6 months at 37°C, less in wet environments.
High Blood Levels: Extremely high levels may indicate cancer.

Semen: Colorimetric Assay for AP

Hydrolysis of Phosphate: Acid phosphatase hydrolyzes the phosphate ester making it useful in identifying semen. This procedure is often tested as presumptive.
Substrate Reaction: α-naphthyl phosphate is the substrate.

Semen: Colorimetric Assay Procedure

Process: Transfer stain to a swab or filter paper, add AP spot solution, and observe for purple colouration within 1 minute.

Semen: Microscopy

Confirmatory Test: Used for conclusive identification.
Procedure: Transfer cells to a microscope slide, heat-fix, apply Christmas tree stain (2 dyes staining nuclei and membranes).
Identifying Components: Cells (sperm, epithelial), debris.

Semen: Sperm Hy-Liter

Immuno fluorescence staining kit: Identifies human sperm heads. Detection happens in seconds, it is used in conjunction with other stains.

Saliva

Production: 1.0 to 1.5 liters daily.
Composition: Mostly water, electrolytes, antibodies, buffers, glycoproteins, enzymes. Includes amylase enzyme, which begins to break down food.
Amylase Isomers: Pancreatic α-amylase is made by the pancreas (HPA). Salivary α-amylase is made by the salivary glands (HSA).

Saliva Presence Testing

Visual Examination: ALS can be used to detect saliva stains within a range of 470-555 nm.
Immunochromatographic Assay: Uses human α-amylase detecting cassettes for presumptive identification.
Stability: Stable for a few weeks to a few months.
Amylase Activity: Also found in breast milk, tears, blood, vaginal secretions, semen, sweat, and urine

Standard Operating Procedures (SOP)

Purpose & Steps: Outlines the steps for laboratory tests, but not the overall purpose.
Validation: Requires proper validation before use, demonstrated at that lab.
Review & Modifications: Reviewed during laboratory audits, deviations are tracked and approved.
Incompetence: Lack of SOP adherence can make an individual appear incompetent.

Additional Equipment

Microscopes: Important for observing bodily fluids' details. Types include:Stereomicroscopes, compound microscopes and comparison microscopes.

Microscopy Descriptions

Stereomicroscope: Visualizes 3D objects, offering magnification up to 60 times. Commonly used for initial observations, identifying color, texture, and thickness.
Compound Microscope: A common type that transmits light through a sample for detail at different magnifications.
Comparison Microscope: Used to view two objects simultaneously, aiming to show similarities and possible shared origin.

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Description

Dive into the fundamental concepts of serology in forensic science with this quiz. Explore the differences between presumptive and confirmatory tests, the importance of body fluids, and the components of blood. Perfect for students and professionals looking to test their knowledge in forensic serological techniques.