Blood Physiology Experiments

Measurement of Hematocrit (Packed Cell Volume)

• Definition and Overview:

  • Hematocrit, or Packed Cell Volume (PCV), represents the percentage ratio of shaped elements (erythrocytes, leucocytes, and thrombocytes) to the total volume of whole blood.

  • Because erythrocytes constitute over $99\%$ of all circulating blood cells, hematocrit serves as an index of red blood cell mass and oxygen-carrying capacity.

• Required Materials:

  • Sterile disposable lancet.

  • Cotton saturated with alcohol ($70\%$\text{ ethanol or isopropyl alcohol}).

  • Dry sterile cotton.

  • Heparinized capillary tubes (distinguished by a red-coded ring at the tip, containing dried anticoagulant to prevent clotting during microhematocrit sampling).

  • Heat source (Bunsen burner flame) or glazier's putty / sealing clay.

  • Microhematocrit centrifuge.

  • Microhematocrit reader ruler or reader card.

• Capillary Blood Collection and Sealing Procedure:

  • The distal phalanx of a finger is disinfected using cotton saturated with alcohol and allowed to air dry.

  • The fingertip is punctured using a sterile lancet to produce free-flowing capillary blood.

  • A heparinized capillary tube is held horizontally or angled slightly downwards to touch the drop of blood.

  • Capillary action draws blood into the tube until it is approximately $\frac{3}{4}$ filled.

  • The bloodless end of the capillary tube is sealed either by gently rotating the tip in a flame to melt the glass closed, or by embedding the tip firmly into glazier's putty.

• Centrifugation Parameters:

  • Capillary tubes are placed in the radial grooves of the microhematocrit centrifuge rotor with the sealed ends directed outward toward the perimeter.

  • Centrifugation is executed under either of two validated protocols:

  • Centrifugation at $12000\,\text{rpm}$ for $5\,\text{minutes}$.

  • Centrifugation at $8000\,\text{rpm}$ for $15\,\text{minutes}$.

  • Centrifugation stratifies blood into three distinct compartments:

  • Upper layer: Clear, amber-yellow blood plasma.

  • Middle layer (buffy coat): A thin, whitish-gray layer containing leucocytes and platelets.

  • Lower packed layer: Densely packed erythrocytes.

• Reading and Measurement with Hematocrit Ruler:

  • The centrifuged capillary tube is placed onto the reading device.

  • The bottom interface of the packed erythrocyte column is aligned precisely with the zero ($0$) baseline.

  • The upper meniscus of the plasma column is aligned with the $100$ ($1.0$) line.

  • The value at the interface between the top of the packed red cell column and the buffy coat is read directly on the scale as the hematocrit percentage ($\%$).

• Physiological Reference Values across Species:

  • Human Male: $46\%$ (reference range: $40-54\%$).

  • Human Female: $42\%$ (reference range: $37-47\%$).

  • Cattle: $35\%$ (reference range: $24-45\%$).

  • Sheep: $35\%$ (reference range: $27-45\%$).

  • Dog: $34\%$ (reference range: $32-36\%$).

  • Horse (Hot-blooded): $41\%$ (reference range: $32-53\%$).

  • Horse (Cold-blooded): Average within range: $24-44\%$.

• Clinical Interpretation:

  • Decreased PCV: Indicates a reduction in circulating erythrocyte mass, characteristic of anemia (e.g., $Fe^{2+}$ iron-deficiency anemia, blood loss, or hemolysis).

  • Increased PCV: Reflects an elevated proportion of circulating erythrocytes, termed polycythemia (seen in dehydration, hemoconcentration, chronic hypoxia, or myeloproliferative disorders).

Hemocytometry: Erythrocyte Count

• Principles and Materials:

  • Erythrocyte counting determines the absolute number of red blood cells in $1\,\text{mm}^3$ of whole blood ($10^6/\text{mm}^3$).

  • Erythrocyte Dilution Pipette (Melangeur): Features a capillary stem graduated to $0.5$ and $1$, an expanded bulb containing a red glass mixing bead, and an upper graduation mark at $101$.

  • Hayem Solution: An isotonic diluting fluid that prevents hemolysis, preserves erythrocyte shape, and prevents cellular clumping.

  • Thoma / Improved Neubauer Counting Chamber: A specialized thick glass slide with ruled grids of known depth and dimensions ($\text{depth} = \frac{1}{10}\,\text{mm}$, small square area = $\frac{1}{400}\,\text{mm}^2$).

• Step-by-Step Procedure:

  • Capillary blood is aspirated into the erythrocyte pipette up to the $0.5$ mark.

  • Any excess blood clinging to the exterior tip of the pipette is carefully wiped clean without drawing blood out of the lumen.

  • Hayem solution is immediately drawn up into the pipette until the fluid meniscus reaches exactly the $101$ mark.

  • The total dilution achieved in the bulb is $1:200$ (blood volume $0.5$ diluted to bulb volume $100$, excluding the stem volume of $1.0$).

  • The pipette is detached from its rubber suction tube, held horizontally between thumb and forefinger, and shaken rhythmically for $3-5\,\text{minutes}$ to ensure thorough suspension.

  • The first $2-3\,\text{drops}$ expelled from the pipette are discarded because the stem contains purely unmixed diluting fluid.

  • A coverslip is positioned over the polished grid platform of the Thoma chamber.

  • A small droplet of the thoroughly mixed suspension is applied to the edge of the coverslip, filling the counting chamber by capillary action without overflowing into the moats or generating air bubbles.

  • The chamber is allowed to stand undisturbed for a few minutes so erythrocytes settle onto the grid surface.

• Counting Rules on the Thoma Grid:

  • Cells are counted under the microscope using high magnification ($40\times$ objective).

  • The counting field consists of $5$ medium squares located within the central large square (the four corners and one central medium square).

  • Each medium square consists of $16$ small squares; therefore, a total of $5 \times 16 = 80$ small squares are counted.

  • Inclusion/Exclusion Rule: Only erythrocytes located inside the small square and those touching or overlapping the left and top border lines (marked by blue crosses) are counted. Cells touching the right and bottom border lines are strictly excluded to avoid duplicate counting.

  • The operator counts the four small squares of the top row from left to right, moves down to the second row and counts across, continuing in a boustrophedon pattern until all $16$ small squares of the medium square are completed.

• Mathematical Calculation Formula:

  • Volume of one small square:     $\text{Volume} = \text{Area} \times \text{Depth} = \frac{1}{400}\,\text{mm}^2 \times \frac{1}{10}\,\text{mm} = \frac{1}{4000}\,\text{mm}^3$

  • Total volume of $80$ small squares counted:     $\text{Total Volume} = 80 \times \frac{1}{4000}\,\text{mm}^3 = \frac{80}{4000}\,\text{mm}^3 = \frac{1}{50}\,\text{mm}^3$

  • Dilution factor = $200$.

  • Derivation of erythrocytes in $1\,\text{mm}^3$:     $\text{Number of Erythrocytes (per } 1\,\text{mm}^3\text{)} = \frac{\text{Erythrocytes counted} \times 200 \times 4000}{80}$     $\text{Number of Erythrocytes (per } 1\,\text{mm}^3\text{)} = \text{Erythrocytes counted} \times 10000$

• Physiological Reference Values ($10^6/\text{mm}^3$):

  • Human Male: $5.4 \times 10^6/\text{mm}^3$ (range: $4.5-6.0 \times 10^6/\text{mm}^3$).

  • Human Female: $4.8 \times 10^6/\text{mm}^3$ (range: $4.0-5.5 \times 10^6/\text{mm}^3$).

  • Cattle: $7.0 \times 10^6/\text{mm}^3$ (range: $5.0-12.0 \times 10^6/\text{mm}^3$).

  • Sheep: $12.0 \times 10^6/\text{mm}^3$ (range: $8.0-16.0 \times 10^6/\text{mm}^3$).

  • Dog: $6.8 \times 10^6/\text{mm}^3$ (range: $5.5-8.5 \times 10^6/\text{mm}^3$).

  • Horse: $9.5 \times 10^6/\text{mm}^3$ (range: $6.5-12.5 \times 10^6/\text{mm}^3$).

• Factors Influencing Erythrocyte Numbers:

  • Anemia: Significant decrease below normal physiological baseline.

  • Polycythemia: Pathological or compensatory elevation in red blood cell count.

  • Physiological Variations: Differences arise depending on animal species, breed/race, sex (males higher than females due to androgens), age (young vs. adult), high geographic altitude (hypoxia-driven erythropoietin release), and functional status (muscular work/exercise releases splenic reserves versus resting state).

Hemocytometry: Leucocyte Count

• Principles and Materials:

  • Leucocyte counting determines the concentration of white blood cells in $1\,\text{mm}^3$ of whole blood ($10^3/\text{mm}^3$).

  • Leucocyte Dilution Pipette (Melangeur): Characterized by a white glass mixing bead in the bulb, stem graduations up to $0.5$ and $1$, and a top marking of $11$.

  • Türk Solution: A diluting and lysing fluid consisting of $1-2\%$ glacial acetic acid (which rapidly lyses non-nucleated erythrocytes) and gentian violet or methylene blue (which selectively stains leucocyte nuclei purple-blue, facilitating visualization).

  • Thoma Counting Chamber: Same standard hemocytometer depth ($\frac{1}{10}\,\text{mm}$).

• Step-by-Step Procedure:

  • Capillary blood is drawn into the leucocyte pipette up to the $1$ mark.

  • The tip is wiped clean.

  • Türk solution is aspirated until the fluid meniscus reaches line $11$.

  • The resulting dilution factor in the bulb is $1:10$ ($1\,\text{part blood}$ diluted to $10\,\text{parts}$ total volume in the mixing chamber).

  • The pipette is shaken vigorously for $3-5\,\text{minutes}$.

  • The first $2-3\,\text{drops}$ from the stem are discarded.

  • A drop of the stained mixture is charged onto the Thoma slide covered with a coverslip.

  • The chamber rests for a few minutes to allow leucocytes to settle evenly.

• Counting and Calculation:

  • Leucocytes are counted throughout the entire large square area ($400$ small squares total, equivalent to four large corner primary squares of $1\,\text{mm}^2$ each, or the full $16$ grouped squares across the grid).

  • Derivation of formula based on volume and dilution:     $\text{Volume counted} = 400 \times \frac{1}{4000}\,\text{mm}^3 = \frac{400}{4000}\,\text{mm}^3 = \frac{1}{10}\,\text{mm}^3$     $\text{Dilution factor} = 10$     $\text{Number of Leucocytes (per } 1\,\text{mm}^3\text{)} = \frac{\text{Leucocytes counted} \times 10 \times 4000}{400}$     $\text{Number of Leucocytes (per } 1\,\text{mm}^3\text{)} = \text{Leucocytes counted} \times 100$

• Physiological Reference Values ($10^3/\text{mm}^3$):

  • Human: $7.0 \times 10^3/\text{mm}^3$ (range: $5.0-10.0 \times 10^3/\text{mm}^3$).

  • Cattle: $8.0 \times 10^3/\text{mm}^3$ (range: $4.0-12.0 \times 10^3/\text{mm}^3$).

  • Sheep: $4.0 \times 10^3/\text{mm}^3$ (range: $2.5-7.5 \times 10^3/\text{mm}^3$).

  • Dog: $11.5 \times 10^3/\text{mm}^3$ (range: $6.0-17.0 \times 10^3/\text{mm}^3$).

  • Horse: $9.0 \times 10^3/\text{mm}^3$ (range: $5.5-12.5 \times 10^3/\text{mm}^3$).

• Clinical Interpretations:

  • Leukocytosis (Elevation): Commonly stimulated by systemic acute bacterial infections, inflammation, tissue necrosis, or leukemia.

  • Leukopenia (Depression): Commonly caused by severe viral infections, bone marrow toxicity, or overwhelming sepsis.

Hemoglobin Measurement by Sahli's Acid Hematin Method

• Principle of the Method:

  • Hydrochloric acid ($0.1\,\text{N HCl}$) reacts with hemoglobin released from lysed red blood cells, converting it into a golden-brown compound known as acid hematin (hemin chloride / hemin chlorur).

  • The resulting brown solution is diluted progressively with distilled water until its color intensity matches the tint of permanent tinted glass comparator standard prisms built into the instrument housing.

• Apparatus and Reagents:

  • Sahli Hemoglobinometer: Housing unit containing standard lateral brown comparison glass plates and a central slot for the Sahli tube.

  • Sahli Graduated Tube: Calibrated with dual scales indicating hemoglobin concentration in grams per $100\,\text{ml}$ ($g/100\,\text{ml}$ or $g/\text{dL}$) and percentage ($\%$).

  • Hemoglobin Pipette: Capillary pipette calibrated to draw exactly $20\,\mu\text{l}$ ($0.02\,\text{ml}$ or $20\,\text{mm}^3$).

  • Glass Stirring Rod: Thin glass rod used to mix contents without splashing.

  • Reagents: $0.1\,\text{N HCl}$ (hydrochloric acid) and pure distilled water.

• Step-by-Step Procedure:

  • $0.1\,\text{N HCl}$ is dispensed into the graduated Sahli tube up to the lower mark (graduation line $2$).

  • Capillary blood is drawn up into the hemoglobin pipette precisely to the $20\,\mu\text{l}$ ($0.02\,\text{ml}$) graduation line.

  • The external surface of the pipette tip is wiped clean.

  • The pipette is inserted deep into the tube near the surface of the acid, and the blood is expelled smoothly without introducing bubbles.

  • The pipette lumen is rinsed several times by aspirating and expelling the acid solution.

  • The mixture is stirred with the glass rod and allowed to incubate for complete conversion of hemoglobin to acid hematin (indicated by color change).

  • Distilled water is added drop by drop using a dropper.

  • After every single drop added, the solution is stirred thoroughly using the glass rod, and the color of the fluid column is compared against the standard side panels against daylight.

  • Drops are added sequentially until the solution's color precisely matches the standard plates.

  • The true hemoglobin reading is identified as the concentration value on the meniscus immediately before the solution becomes lighter than the comparator block.

• Physiological Reference Values ($g/100\,\text{ml}$):

  • Human Male: $16\,g/100\,\text{ml}$ (range: $14-18\,g/100\,\text{ml}$).

  • Human Female: $14\,g/100\,\text{ml}$ (range: $12-16\,g/100\,\text{ml}$).

  • Cattle: $12\,g/100\,\text{ml}$ (range: $9-15\,g/100\,\text{ml}$).

  • Sheep: $12\,g/100\,\text{ml}$ (range: $10-15\,g/100\,\text{ml}$).

  • Dog: $14\,g/100\,\text{ml}$ (range: $11-17\,g/100\,\text{ml}$).

  • Horse: $15\,g/100\,\text{ml}$ (range: $11-19\,g/100\,\text{ml}$).

Wintrobe Erythrocyte Indices

• Mean Corpuscular Volume (MCV):

  • Defines the average volume of an individual erythrocyte in cubic micrometers ($\mu\text{m}^3$ or femtoliters, $\text{fL}$).

  • Formula:     $\text{MCV}\,(\mu\text{m}^3) = \frac{\text{Hematocrit (\%)} \times 10}{\text{Number of Erythrocytes (in } 10^6/\text{mm}^3\text{)}}$

  • Morphological Classification:

  • Normocytic Anemia: Erythrocyte volume falls within the normal physiological range despite an overall reduction in circulating red cell numbers or hematocrit.

  • Microcytic Anemia: MCV is smaller than normal; commonly seen in iron-deficiency anemia and chronic blood loss.

  • Macrocytic Anemia: MCV is larger than normal; typical of vitamin $B_{12}$ or folate deficiencies.

• Mean Corpuscular Hemoglobin (MCH):

  • Quantifies the absolute average weight of hemoglobin contained within a single erythrocyte, expressed in picograms ($\text{pg}$).

  • Formula:     $\text{MCH}\,(\text{pg}) = \frac{\text{Hemoglobin (in } g/100\,\text{ml}) \times 10}{\text{Number of Erythrocytes (in } 10^6/\text{mm}^3\text{)}}$

  • Morphological Classification:

  • Normochromic: Hemoglobin content per cell is normal.

  • Hypochromic Anemia: Value is less than normal; cells exhibit enlarged central pallor due to deficient hemoglobin synthesis.

  • Hyperchromic Anemia: Value is mathematically higher than normal (often associated with abnormally large macrocytic cells or cellular dehydration/spherocytosis).

• Mean Corpuscular Hemoglobin Concentration (MCHC):

  • Expresses the average concentration of hemoglobin contained in a unit volume of packed red blood cells, stated as a percentage ($\%$ or $g/\text{dL}$).

  • Formula:     $\text{MCHC}\,(\%) = \frac{\text{Hemoglobin (in } g/100\,\text{ml}) \times 100}{\text{Hematocrit (\%)}}$

  • Morphological Classification:

  • Normochromic Anemia: Hemoglobin concentration within red cells is normal.

  • Hypochromic Anemia: True cellular hemoglobin concentration is below physiological limits.

  • Hyperchromic State: Concentration is reported higher than normal.

Blood Smear Preparation and Differential Leucocyte Formula

• Preparation of Blood Smear (Froti Yapımı):

  • A clean, grease-free glass microscope slide is placed flat on a clean surface.

  • A single small drop of fresh capillary or uncoagulated blood is placed near the narrow margin of the slide.

  • A second glass slide (spreader slide) is held at an angle of approximately $30-45^\circ$, brought back against the blood droplet until the fluid spreads laterally along the interface.

  • The spreader slide is pushed forward smoothly and rapidly along the length of the slide, creating a uniform, paper-thin blood film terminating in a feathered edge (monolayer).

  • The smear is air-dried immediately.

• Staining Protocols and Indications:

  • Staining Methods: May-Grünwald-Giemsa mix staining or Giemsa staining.

  • Diagnostic Indications:

  • Calculating the differential leucocyte formula (relative percentages of white blood cell subsets).

  • Microscopic detection and identification of intra-erythrocytic or extracellular hemoparasites (e.g., Babesia, Anaplasma, Trypanosoma).

  • Qualitative assessment of erythrocyte morphology, anisocytosis, poikilocytosis, and hemoglobin density (hypochromasia).

• Differential Leucocyte Counting Method (Leucocyte Formula):

  • The blood smear is scanned systematically under the oil immersion objective ($100\times$) along a continuous battlement or serpentine zigzag track within the monolayer.

  • Ten consecutive white blood cells are classified and tabulated across each designated track segment.

  • A total of $100$ consecutive leucocytes are identified to determine the relative percentage ($\%$) of each leukocyte class.

• Species Predominance Patterns:

  • Neutrophil-Predominant Species: Humans, horses, and dogs (neutrophils form the largest percentage of circulating leucocytes).

  • Lymphocyte-Predominant Species: Ruminants, including cattle, sheep, and goats (lymphocytes form the primary circulating leucocyte fraction).

• Morphology and Functional Characteristics of Specific Leucocytes:

  • Neutrophils:

  • Form the most abundant granulocytic population.

  • Characterized by pale pinkish-blue cytoplasm filled with fine secondary granules.

  • Nuclei stain deep purple and exhibit varied shapes: mature segmented forms have $3-5$ distinct lobes connected by delicate chromatin filaments; immature band forms possess a curved, horseshoe-like nucleus without distinct constrictions.

  • Highly motile, active phagocytes specializing in neutralizing and digesting invading bacteria.

  • Termed heterophils in avian species.

  • Absolute counts increase sharply during acute bacterial infections and tissue trauma (neutrophilia).

  • Eosinophils:

  • Cytoplasm is packed with large, spherical, red-to-orange-red acidophilic granules.

  • In equine blood, granules are large and clustered, giving a distinct "blackberry" (mulberry) appearance.

  • Typically possess a bilobed nucleus.

  • Normally present in low numbers; decrease in response to elevated glucocorticoid stress.

  • Proliferate and increase during parasitic infections and allergic reactions.

  • Basophils:

  • Represent the least abundant circulating leucocyte type ($0.5-1\%$ of total white blood cells).

  • Cytoplasm and nucleus are densely packed with coarse, water-soluble, dark blue-to-purple metachromatic granules.

  • Granules contain high concentrations of histamine and heparin.

  • Play prominent roles in immediate hypersensitivity reactions and increase in chronic inflammation.

  • Lymphocytes:

  • Mononuclear agranulocytes characterized by a smooth, rounded cellular perimeter.

  • Features a dense, spherical, dark-purple nucleus occupying nearly the entire cell volume, bounded by a very thin rim of clear sky-blue cytoplasm.

  • Morphologically separated into small and large varieties; completely devoid of phagocytic capabilities.

  • B Lymphocytes: Differentiate into antibody-producing plasma cells; mediate humoral immunity.

  • T Lymphocytes: Mediate antigen-specific cellular immunity, defending against intracellular bacteria, viral infections, and fungi.

  • Monocytes:

  • Largest leucocyte found in peripheral circulation.

  • Cell border is irregular or amoeboid, containing abundant grayish-blue cytoplasm with ground-glass texture.

  • Nucleus is large, eccentric, indented, kidney-shaped, or horseshoe-shaped, staining lighter purple with an open chromatin mesh.

  • Migrate into tissues to transform into long-lived macrophages; numbers increase during chronic systemic infections.

Coagulation Time Determination

• Capillary Tube Method Principle:

  • Evaluates the intrinsic and common coagulation pathways by monitoring the chronological emergence of visible fibrin threads as blood coagulates inside a plain capillary tube.

• Step-by-Step Procedure:

  • The skin of the fingertip is disinfected and punctured with a sterile lancet.

  • Crucial Step: The first emerging drop of blood is wiped away and discarded, because it contains released tissue thromboplastin from damaged cells, which prematurely activates coagulation mechanisms.

  • Blood is collected into a non-heparinized, untreated (plain) glass capillary tube until completely filled.

  • A stopwatch is started immediately as blood enters the tube.

  • The tube is held undisturbed for an initial period of $2\,\text{minutes}$.

  • Starting at the two-minute mark, approximately $1\,\text{cm}$ of the glass tube is snapped off from one tip.

  • If no fibrin strands bridge the broken glass ends, the tube is held for another $30\,\text{seconds}$ and snapped again.

  • This sequential breaking is repeated every $30\,\text{seconds}$ until fine, gelatinous, thread-like strands of fibrin span across the fracture gap.

  • The precise interval from blood collection to the initial visual appearance of fibrin threads is recorded as the coagulation time.

• Physiological Reference Ranges across Species:

  • Human: $2-6\,\text{minutes}$.

  • Cattle: $4-15\,\text{minutes}$.

  • Sheep: $3\,\text{minutes}$.

  • Dog: $3-13\,\text{minutes}$.

  • Horse (At): $4-15\,\text{minutes}$.

• Etiologies of Prolonged Coagulation Time:

  • Ingestion of spoiled sweet clover hay containing mold-derived dicoumarol.

  • Dicoumarol (coumarin) toxicity.

  • Severe systemic viral diseases damaging vascular or hepatic tissues.

  • Severe thrombocytopenia (platelet deficiency).

  • Vitamin K deficiency (impairing hepatic carboxylation of factors II, VII, IX, and X).

  • Severe acute or chronic liver disease (reducing synthesis of circulating pro-coagulant proteins).

  • Hemophilia (inherited deficiencies of clotting factors, such as factor VIII or factor IX).

• Physical and Environmental Modulators:

  • Temperature: An increase in environmental temperature accelerates enzymatic cascade velocity, decreasing coagulation time.

  • Blood Pressure: An elevation in blood pressure increases bleeding intensity and prolongs coagulation time.

Blood Grouping and Immunohematology

• ABO and Rh Determination Procedure:

  • Two clean glass slides are labeled: Slide 1 is marked "Anti-A" on the left side and "Anti-B" on the right side; Slide 2 is marked "Anti-D" in the center.

  • Capillary blood obtained by sterile lancet puncture is placed as three distinct droplets:

  • One drop on the left zone of Slide 1 (Anti-A section).

  • One drop on the right zone of Slide 1 (Anti-B section).

  • One drop in the center of Slide 2 (Anti-D section).

  • Corresponding diagnostic commercial antisera are added beside the respective blood drops:

  • Anti-A test serum to the Anti-A area.

  • Anti-B test serum to the Anti-B area.

  • Anti-D test serum to the Anti-D area.

  • Using distinct, clean glass rods or toothpicks for each test zone, the blood and antiserum are mixed thoroughly to cover a circular area of $1.5-2\,\text{cm}$ in diameter.

  • The slides are rotated gently and observed for $1-2\,\text{minutes}$ for macroscopically visible agglutination (clumping of red blood cells into discrete granules or flakes).

  • Because Anti-D antibodies (IgG-type) often agglutinate erythrocytes more slowly, the slide containing Anti-D is placed inside the warm palm of the hand to supply gentle physiological heating ($\approx 37^\circ\text{C}$), accelerating antigen-antibody binding.

• Interpretation Criteria for Human ABO and Rh Blood Groups:

  • Agglutination in Anti-A only = Blood Group A.

  • Agglutination in Anti-B only = Blood Group B.

  • Agglutination in both Anti-A and Anti-B = Blood Group AB.

  • No agglutination in either Anti-A or Anti-B = Blood Group O.

  • Agglutination in Anti-D = Rh-positive ($Rh^+$).

  • Absence of agglutination in Anti-D = Rh-negative ($Rh^-$).

• Basic Transfusion Compatibility Principles:

  • Universal Donor: Group O, because its erythrocytes lack both A and B surface agglutinogens, allowing them to escape attack by recipient ABO isoantibodies.

  • Universal Receiver: Group AB, because recipient serum lacks circulating anti-A and anti-B isoantibodies, permitting safe receipt of donor erythrocytes.

• Animal Blood Group Systems:

  • Cattle: Feature $12$ distinct blood group genetic systems and over $100$ documented specific test sera.

  • Sheep: Possess $8$ recognized blood group systems and $25-30$ specialized testing antisera.

  • Dogs: Characterized by $8$ primary blood group systems (the DEA — Dog Erythrocyte Antigen system) and $10$ anti-test sera.

  • Horses: Possess $8$ defined blood group systems evaluated using approximately $25$ test sera.

• Pathophysiology of Erythroblastosis Fetalis (Hemolytic Disease of the Newborn):

  • Genetic Setting: Occurs when an $Rh^-$ mother carries an $Rh^+$ fetus (the father being genetically $Rh^+$).

  • Sensitization Phase: Although maternal and fetal blood circuits remain strictly separated by placental barriers during normal gestation, microtrauma or placental membrane rupture during parturition allows fetal $Rh^+$ erythrocytes to enter maternal circulation.

  • Maternal Immune Response: Fetal D-antigen is processed as foreign by the mother's immune system, resulting in the primary production of maternal Anti-D agglutinins (IgG antibodies).

  • Secondary Hemolytic Attack: In a subsequent pregnancy with an $Rh^+$ fetus, maternal Anti-D IgG molecules readily cross the placental membrane into fetal blood, binding tightly to the fetal $Rh^+$ erythrocyte membranes.

  • Hemolysis and Pathology: Fetal red cells undergo agglutination and destructive hemolysis. To compensate for massive erythrocyte loss, the fetal hematopoietic organs (bone marrow, spleen, and liver) release large numbers of immature, nucleated red blood cells (erythroblasts) into the bloodstream.

  • Clinical Consequence: Results in profound fetal anemia, hepatosplenomegaly, severe jaundice (icterus gravis neonatorum), kernicterus, and intrauterine fetal hydrops or death in severe untreated cases.

Erythrocyte Osmotic Fragility Test

• Physiological Principle:

  • Evaluates the resistance of erythrocytes to hypotonic hemolysis when suspended in progressively diluted sodium chloride ($\text{NaCl}$) solutions.

  • When red cells are placed into hypotonic saline, an osmotic gradient drives water into the cytoplasm, causing cell swelling, transformation into fragile spherocytes, membrane disruption, and hemolysis with release of hemoglobin.

  • Microcytic red blood cells possess an increased surface-area-to-volume ratio and resist osmotic lysis at lower salt concentrations.

  • NESTROFT (Naked Eye Single Tube Red cell Osmotic Fragility Test): A rapid screening test utilizing blood anticoagulated with EDTA.

• Number of Test Tubes Used by Species:

  • Cattle: $12\,\text{tubes}$.

  • Horse: $15\,\text{tubes}$.

  • Dog: $9\,\text{tubes}$.

• Preparation of Hypotonic Serial Dilutions in Cattle:

  • Solutions are prepared in a sequential series with a constant concentration difference of $0.02\%$ between neighboring tubes.

  • Tube 1 (Control): Contains $1.0\,\text{cc}$ of $0.85\%\,\text{NaCl}$ (physiological saline; isotonic control; no distilled water added).

  • Tube 2: $0.60\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.40\,\text{cc}$ of distilled water ($0.60\%\,\text{NaCl}$).

  • Tube 3: $0.58\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.42\,\text{cc}$ of distilled water ($0.58\%\,\text{NaCl}$).

  • Tube 4: $0.56\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.44\,\text{cc}$ of distilled water ($0.56\%\,\text{NaCl}$).

  • Tube 5: $0.54\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.46\,\text{cc}$ of distilled water ($0.54\%\,\text{NaCl}$).

  • Tube 6: $0.52\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.48\,\text{cc}$ of distilled water ($0.52\%\,\text{NaCl}$).

  • Tube 7: $0.50\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.50\,\text{cc}$ of distilled water ($0.50\%\,\text{NaCl}$).

  • Tube 8: $0.48\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.52\,\text{cc}$ of distilled water ($0.48\%\,\text{NaCl}$).

  • Tube 9: $0.46\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.54\,\text{cc}$ of distilled water ($0.46\%\,\text{NaCl}$).

  • Tube 10: $0.44\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.56\,\text{cc}$ of distilled water ($0.44\%\,\text{NaCl}$).

  • Tube 11: $0.42\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.58\,\text{cc}$ of distilled water ($0.42\%\,\text{NaCl}$).

  • Tube 12: $0.40\,\text{cc}$ of $1\%\,\text{NaCl}$ mixed with $0.60\,\text{cc}$ of distilled water ($0.40\%\,\text{NaCl}$).

• Incubation and Testing Procedure:

  • Exactly $1\,\text{drop}$ of fresh whole blood is introduced into each of the $12\,\text{tubes}$ using a Pasteur pipette.

  • Each tube is gently shaken to disperse erythrocytes uniformly.

  • The tubes incubate undisturbed at standard room temperature ($25^\circ\text{C}$) for $2\,\text{hours}$.

• Evaluation and Assessment of Hemolysis:

  • Tubes are held up to ambient daylight with a printed paper placed directly behind them.

  • Intact Erythrocytes (No Hemolysis): Unlysed red cells scatter and reflect light, rendering the suspension cloudy and completely opaque (text behind the tube cannot be read).

  • Partial Hemolysis: Only the most fragile red blood cells lyse; the fluid becomes translucent.

  • Complete Hemolysis: All erythrocytes rupture, releasing free hemoglobin into solution and rendering the liquid transparent and clear red ("wine red"), allowing text behind the tube to be read clearly.

  • Reading Steps:

  • The control tube (Tube 1) is inspected first; it must show zero hemolysis.

  • Minimal Durability (Initial Resistance): Recorded as the salt concentration ($\text{NaCl} \,\%$) in the specific tube where hemolysis first begins (indicated by a faint reddish tint in the supernatant).

  • Maximal Durability (Complete Resistance): Recorded as the salt concentration ($\text{NaCl} \,\%$) in the tube where total hemolysis occurs, characterized by a completely transparent, clear wine-red liquid with zero intact sedimented cells.