Forensic Serology: Blood Composition, Testing, and Typing

Comprehensive vocabulary flashcards covering blood composition, white blood cell classifications, presumptive and confirmatory blood tests, human species determination methods, and ABO/Rhesus blood typing systems.

Blood

A specialised connective tissue responsible for transporting substances throughout the body, with humans possessing approximately $4.7\,\text{L}$.

Plasma

The liquid portion of blood comprising approximately $55\%$ of whole blood volume, composed of approximately $91\text{–}92\%$ water, $7\%$ proteins, and $1\text{–}2\%$ other dissolved substances.

Formed elements

The cellular fraction of blood making up approximately $45\%$ of whole blood volume, consisting of red blood cells, white blood cells, and platelets.

Buffy coat

The middle layer observed after blood centrifugation that is composed of white blood cells and platelets.

Albumin

The major plasma protein accounting for $55\text{–}57\%$ of plasma proteins that maintains osmotic pressure, regulates fluid distribution, and transports fatty acids and drugs.

Globulins

Plasma proteins constituting approximately $38\%$ of total plasma proteins that function in substance transport and immune defence.

Alpha ($\alpha$) globulins

A subcategory of globulin plasma proteins that function as enzymes and transport proteins.

Beta ($\beta$) globulins

A subcategory of globulin plasma proteins responsible for transporting proteins and assisting in immune targeting.

Gamma ($\gamma$) globulins

A subcategory of globulin plasma proteins composed of antibodies that defend the body against foreign substances.

Fibrinogen

A plasma protein ($4\%$ in the lecture diagram; $6.5\%$ on slide 10) converted into fibrin to form a stabilizing mesh during blood clotting.

Prothrombin

A clotting-related plasma protein ($1\%$ in the lecture diagram) that is converted into thrombin during coagulation.

Erythrocytes (RBCs)

Biconcave, non-nucleated formed elements lacking mitochondria that contain haemoglobin and carbonic anhydrase, having an approximate lifespan of $120\,\text{days}$.

Haematocrit

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

Haemostasis

The physiological process of stopping bleeding through four stages: blood vessel injury, vessel spasm (constriction), platelet adhesion and aggregation, and fibrin formation and coagulation.

Thrombocytes (platelets)

Small, non-nucleated fragments of megakaryocytes produced in the bone marrow that function in haemostasis and blood clot formation.

Granulocytes

A category of white blood cells originating in the bone marrow that possess visible granules; includes neutrophils, eosinophils, and basophils.

Agranulocytes

A category of white blood cells lacking prominent cytoplasmic granules; includes lymphocytes and monocytes.

Neutrophils

The most abundant granulocytes ($50\text{–}70\%$ of WBCs) featuring a multi-lobed nucleus and fine granules, functioning in phagocytosis and releasing destructive enzymes and phagocyte-attracting signals.

Eosinophils

Granulocytes ($2\text{–}4\%$ of WBCs) characterized by a bilobed nucleus and prominent granules containing RNase, DNase, and lipase, active in parasite defence, allergic reactions, asthma, and phagocytosing antigen–antibody complexes.

Basophils

Granulocytes ($0.5\text{–}1\%$ of WBCs) with darkly stained granules often obscuring the nucleus that mediate allergic and inflammatory reactions via histamine, serotonin, heparin, proteolytic enzymes, and lipid mediators.

Lymphocytes

Agranulocytes ($20\text{–}30\%$ of WBCs) with large round or oval nuclei and thin rims of cytoplasm, divided into B cells (antibody production) and T cells (cell-mediated immunity).

Monocytes

Large agranulocytes characterized by a kidney-shaped or indented nucleus that engage in phagocytosis and differentiate into macrophages.

Presumptive blood test

A preliminary screening test that determines whether an unknown stain could contain blood, usually relying on chemical oxidation reactions linked to the haem group of haemoglobin.

Kastle–Meyer test

A colorimetric presumptive blood test where the iron in haem oxidizes colourless phenolphthalin into pink phenolphthalein in the presence of hydrogen peroxide, with a sensitivity of approximately $1:10{,}000$.

Hemastix test

A presumptive strip test utilizing tetramethylbenzidine (TMB) and peroxide that produces an orange-to-green colour change in the presence of blood.

Fluorescein

A presumptive test reagent requiring zinc and hydrogen peroxide that emits green fluorescence under blue/UV illumination, exhibiting a sensitivity of approximately $1:100{,}000$ and a reaction duration of $5\text{–}7\,\text{minutes}$.

Luminol

A chemiluminescent presumptive reagent reacting with iron, hydrogen peroxide, and potassium hydroxide to emit blue light in dark conditions, with a sensitivity of approximately $1:300{,}000$ and a duration of approximately $30\,\text{seconds}$.

Confirmatory blood test

A definitive analytical procedure used to conclusively establish whether a suspected stain contains blood, such as microscopic crystal tests.

Teichmann test

A confirmatory crystal test for blood that uses acetic acid and chloride to generate characteristic brownish rhomboid crystals upon heating and cooling.

Takayama test

A confirmatory crystal test for blood that uses pyridine and glucose to produce characteristic pink, needle-shaped crystals under microscopic examination.

Precipitin test

An immunological test to identify human blood by injecting human blood into an animal (typically a rabbit) to harvest antibodies, which form a visible precipitation reaction when combined with human blood proteins.

Ouchterlony test

An agar diffusion variation of the precipitin test where antigens and antibodies migrate toward each other to form a visible precipitation line where they react.

ABAcard HemaTrace

A lateral-flow strip test that uses antibodies against human haemoglobin to identify human blood within approximately $10\,\text{minutes}$ at a sensitivity of $1:1{,}000{,}000$.

ABO blood group system

A genetically controlled blood classification system based on the presence of inherited A and B surface antigens on red blood cells and anti-A or anti-B antibodies in plasma.

Rhesus (Rh) blood group system

A blood antigen system involving C, D, and E antigens, where the presence of the D antigen designates Rh-positive blood and its absence designates Rh-negative blood.

Agglutination

The clumping of red blood cells caused by antibodies binding to their corresponding surface antigens during blood typing assays.