Forensic Serology Basics

Identifying specific cell types or stains on an item.

A test that preliminarily suggests the presence of a specific substance.

A test that conclusively confirms the presence of a specific substance.

A positive result when the actual result should be negative.

A negative result when the actual result should be positive.

The liquid component of blood containing water, proteins, minerals, hormones, and antibodies.

Red blood cells, responsible for carrying oxygen to cells and carbon dioxide to the lungs.

The protein in red blood cells that binds oxygen, carbon dioxide, carbon monoxide and cyanide.

White blood cells are responsible for defending the body against infections. They contain a nucleus and are the source of DNA in blood samples.

Platelets are responsible for blood clotting. They clump together at the site of injury to stop bleeding. Unlike white blood cells, they do not contain a nucleus.

A presumptive test for blood uses visual clues to determine if it is likely to be blood, but does not definitively confirm its identity.

A visual examination of blood can reveal certain characteristics, such as its red colour (candy-apple red or deep red), flaky texture when dried, and black appearance under an ultraviolet light.

The Kastle-Meyer test is a colorimetric assay that utilizes a chemical reaction catalyzed by heme (a component of blood) to detect the presence of blood.

The Kastle-Meyer test relies on an oxidation-reduction reaction. In this reaction, phenolphthalin (a colorless reductant) is oxidized by heme in the presence of hydrogen peroxide, resulting in the formation of phenolphthalein and a pink colour.

The Kastle-Meyer test is highly sensitive and can detect blood at very low concentrations. However, it lacks specificity and can generate false positives due to the presence of oxidants or plant peroxidases.

The Kastle-Meyer test can produce false negatives if reductants are present, as these substances interfere with the oxidation reaction and prevent the formation of the pink colour.

A presumptive test for blood that uses a chemical reaction to produce a pink color in the presence of blood.

A presumptive test for blood that uses a chemical reaction to produce light in the presence of blood. This light can be seen when viewing the sample with UV light.

A chemical compound used in the chemiluminescence assay to detect blood. It produces light when it reacts with heme, a component of blood.

A confirmatory test for blood and human blood. Uses antibodies that specifically recognize human antigens to confirm the presence of human blood.

A type of antibody that reacts with specific antigens on a human red blood cell. It is used in the immunochromatographic assay to confirm human blood.

A mixture of antibodies that react with various human antigens. They are used in some immunochromatographic assays.

A specific antibody that reacts with only one site on a human antigen. They are used in some immunochromatographic assays.

Sperm cells are composed of a head, middle piece, and tail. The head contains the nucleus and acrosomal cap, which contains enzymes that help break down the egg during fertilization. The middle piece contains mitochondria to power the tail, which is responsible for mobility.

The acrosomal cap on the sperm head contains enzymes that break down the outer layer of the egg, allowing the sperm to penetrate and fertilize it.

The sperm tail is responsible for its movement. It contains a structure called a flagellum that propels the sperm cell through the female reproductive tract.

The middle piece of a sperm cell contains mitochondria, which are responsible for producing energy for the tail's movement

Microscopy is a confirmatory test for semen because it allows us to see the sperm cells directly under a microscope. We can then identify specific features like the head, middle piece, and tail.

Christmas tree staining is a technique used in microscopy to identify sperm cells. It uses two dyes: red dye, which stains all nuclei and the sperm acrosomal cap, and green dye, which stains the sperm neck and tail, as well as all cell membranes.

Sperm Hy-Liter is an immunofluorescence staining kit that is highly specific and sensitive for identifying human sperm heads. It allows for quick and easy identification of sperm on various samples.

Amylase is an enzyme found in saliva that breaks down carbohydrates, specifically starches. It begins the digestion of food in the mouth.

Saliva is produced by three main salivary glands: the submandibular glands (70%), the parotid glands (25%), and the sublingual glands (5%). It is mainly composed of water, electrolytes, antibodies, buffers, glycoproteins, and enzymes.

The ALS (Alternate Light Source) can be used to search for possible saliva stains. It is not specific for saliva but can reveal stains with fluorescence.

A standardized procedure that outlines the steps for performing a specific test in a laboratory.

A rapid, presumptive test for the presence of blood in a sample using antibodies that bind to a specific blood protein (glycophorin A) and create a visible colored line on a strip.

A process that ensures a laboratory method consistently produces accurate and reliable results. It ensures the method works correctly in that specific lab.

A clear, viscous fluid that mixes with sperm cells to form semen.

A deviation from the written SOP must be documented, approved by a supervisor, and justifiable. Failure to follow this can make results invalid and affect the legal standing of the evidence.

The presence of sperm in semen, the result of the normal production of sperm in the testes.

The amount of semen released during a typical ejaculation, ranging from 2 to 5 milliliters.

A microscope used to visualize three-dimensional objects, often used for initial observations in forensics.

The maturation process sperm undergo in the epididymis lasting approximately 3 months.

A type of microscope that uses light to illuminate and magnify an object placed on a slide.

A type of microscope used to compare two specimens side by side, often in forensic investigations.

The mixing of seminal fluid and sperm cells in the prostatic urethra during ejaculation.

The ability to see details clearly. A stereomicroscope aids in visualizing details of bodily fluids in forensics.

The primary source of seminal fluid, an organ that contributes about 60% of the total ejaculate volume.

Improperly following SOP can make a forensic analyst appear incompetent and unreliable, potentially destroying their career.

A sugar found in seminal fluid, offering energy for sperm.

A key component of seminal fluid, including acid phosphatase (AP) and prostate-specific antigen (PSA) and contributing about 30% of the total ejaculate volume.

An enzyme found in high concentrations in semen, used to differentiate semen from other bodily fluids.

The process of hydrolyzing α-naphthyl phosphate by acid phosphatase, resulting in the formation of a purple precipitate in the presence of brentamine Fast B solution, indicating the presence of semen.

A protein specific to the prostate gland, used for testing the presence of semen in forensic investigation.

A test for the presence of PSA in a sample using antibodies that bind to the protein, producing a visible colored line on a strip, indicating the presence of semen.

A phenomenon that occurs during immunochromatographic assays when a very high concentration of the antigen causes an inaccurate result, making the test line less intense or even invisible.

The surgical removal of a section of the vas deferens, a duct that carries sperm from the testes to the urethra, resulting in a reduced sperm count or the absence of sperm in ejaculate.