Blood and Blood Typing in Forensic Serology

Vocabulary flashcards detailing forensic serology, blood composition, cellular elements, presumptive/confirmatory testing, and blood typing methodologies.

Forensic Serology

The branch of science focused on the recognition and identification of biological stains in legal matters, predominantly involving blood and sexual assault body fluids.

Pluripotent Stem Cell

A single type of primitive cell in the bone marrow from which all blood cells originate.

Plasma

The clear, yellow liquid portion of blood constituting $55\%$ of total volume, composed of $91\text{--}92\%$ water, $7\%$ proteins, and $1\text{--}2\%$ non-proteins/solutes.

Albumin

The most abundant plasma protein (~$55\text{--}57\%$), synthesized in the liver, which transports fatty acids and drugs while regulating osmotic pressure.

Globulins

A family of plasma proteins larger than albumin (~$38\%$), divided into $\alpha$-globulins, $\beta$-globulins, and antibody-producing $\gamma$-globulins.

Fibrinogen

A plasma protein ($4\text{--}6.5\%$) that converts into an insoluble fibrin mesh during injury to promote blood clotting.

Platelets (Thrombocytes)

Irregular, non-nucleated fragments of megakaryocytes measuring $2\text{--}4\,\mu\text{m}$ in diameter that survive $4\text{--}8\,\text{days}$ and function in haemostasis.

Haemostasis

The multi-step physiological mechanism that arrests bleeding through vessel spasm, platelet plug formation, and coagulation via insoluble fibrin strands.

Erythrocytes (Red Blood Cells)

Biconcave, non-nucleated, and mitochondria-free cells with a ~$120\,\text{day}$ lifespan that carry oxygen and carbon dioxide using haemoglobin.

Hematocrit

The percentage of total blood volume occupied by red blood cells, normally measuring approximately $45\%$ in males and $40\%$ in females.

Carbonic Anhydrase

An enzyme present in large quantities inside erythrocytes that catalyses the reaction between carbon dioxide ($\text{CO}_2$) and water.

Neutrophils

Granulocytic white blood cells ($50\text{--}70\%$ of leukocytes) with multi-lobed nuclei that serve as active phagocytes to ingest pathogens and release lytic enzymes.

Eosinophils

Granular leukocytes ($2\text{--}4\%$ of leukocytes) with bi-lobed nuclei that mediate allergic reactions, asthma, and parasitic infections while phagocytosing antigen-antibody complexes.

Basophils

Rare leukocytes ($0.5\text{--}1\%$ of leukocytes) featuring $2\text{--}3$ lobed nuclei packed with dark granules containing histamine, serotonin, and heparin.

T Lymphocytes

Agranulocytic leukocytes responsible for cellular immunity and target cell lysis through cytokines, composed of helper $T$ ($\text{T}_\text{H}$) cells, cytotoxic $T$ ($\text{T}_\text{C}$) cells, and natural killer (NK) cells.

B Lymphocytes

Agranulocytes mediating humoral immunity that proliferate into antibody-secreting plasma cells to neutralize extracellular pathogens.

Monocytes

Large ($14\text{--}20\,\mu\text{m}$) agranular phagocytic cells ($3\text{--}8\%$ of leukocytes) with kidney- or bean-shaped nuclei that differentiate into macrophages upon tissue entry.

Presumptive Tests

Screening tests relying on visible colorimetric or luminescent reactions to indicate whether a suspected stain could be blood.

Kastle-Meyer Test

A presumptive test where iron in haemoglobin catalyses the oxidation of colourless phenolphthalin to pink phenolphthalein in the presence of hydrogen peroxide ($\text{H}_2\text{O}_2$).

Hemastix

A field test strip impregnated with tetramethylbenzidine (TMB) and peroxide that produces an orange-to-green colour transition upon exposure to blood.

Fluorescein

A luminescent reagent (fluorescein + zinc + $\text{H}_2\text{O}_2$) that emits green light under UV radiation in the presence of haem, with a detection threshold around $1:100{,}000$.

Luminol

A luminescent presumptive chemical (luminol + $\text{H}_2\text{O}_2$ + $\text{KOH}$) that emits a blue glow in darkness when catalysed by blood iron, sensitive up to $1:300{,}000$.

Confirmatory Blood Tests

Definitive analytical assays, typically microcrystalline tests, that confirm the presence of blood from volumes as small as $0.001\,\text{mL}$.

Teichmann Test

A confirmatory microcrystal assay utilizing acetic acid and chloride to produce distinctive brownish rhomboid crystals in the presence of blood.

Takayama Test

A confirmatory microcrystalline blood test using pyridine and glucose that forms characteristic pink, needle-shaped crystals.

Precipitin Test

An immunological test identifying human blood origin by evaluating precipitation formed when human blood antigens interact with animal antiserum.

Ouchterlony Test

A gel-based precipitin technique performed in agar plates where diffusing antigens and antibodies form an opaque precipitation line at the zone of equivalence.

ABAcard® HemaTrace®

A rapid anti-human haemoglobin chromatographic test stick showing species-specific reactivity up to a $1:1{,}000{,}000$ dilution within $10\,\text{minutes}$.

ABO Blood Grouping

A genetically determined classification system categorizing blood into types A, B, AB, or O according to surface erythrocyte antigens and serum antibodies.

Rhesus (Rh) Blood System

An erythrocyte antigen classification based on C, D, or E surface molecules, where the presence of the D antigen designates Rh-positive ($\text{Rh}^+$).

Agglutination Assay

A testing technique where blood is blended with known anti-sera (anti-A, anti-B, anti-D) to reveal blood group through visible antigen-antibody clumping.