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Erythrocytes

  • Transport O<em>2O<em>2 and CO</em>2CO</em>2; contain hemoglobin.

  • Lifespan varies by species (Canine: 100-120 days, Feline: ~70 days, Equine: 140-150 days, Avian: 28-45 days).

  • Analysis aids in diagnosing anemias, infections, parasitic burdens.

Automated Analyzers

  • Generate hematologic data for Complete Blood Counts (CBCs).

  • Benefits: Lower cost, reduced labor, more complete information.

  • Count RBCs, WBCs, Platelets; manual counts are rare except in avian/exotic practices.

Polycythemia and Anemia

  • Polycythemia (Erythrocytosis): Increased RBCs, PCV, hemoglobin.

    • Relative: Splenic contraction, dehydration.

    • Primary: Myeloproliferative disorders.

    • Secondary: Renal/lung disorders.

  • Anemia: Decreased blood oxygen-carrying capacity, usually due to decreased circulating RBCs.

Impedance Analyzers

  • Count cells by measuring impedance to electric current flow; current change is a function of cell size.

  • Disadvantages: Cell size variation, misses morphologic abnormalities, inaccuracies with platelet clumping/nucleated RBCs.

Quantitative Buffy Coat (QBC) Analysis System

  • Uses differential centrifugation and staining to estimate cells (hematocrit, WBC, platelet concentrations).

  • Limitation: Provides only estimates; left shift may go undetected.

Laser-Based Flow Cytometer Analyzers

  • Use focused laser beams to evaluate cell size and density based on light scatter.

Combination Methods & Histograms

  • Some analyzers combine laser-based and impedance methods.

  • Histograms show cell distribution and can indicate anomalies.

Manual Cell Counts

  • Rarely performed, except in avian/exotic practices using Leukopet systems and hemocytometers.

Complete Blood Count (CBC) Components

  • Includes: Total RBC count, PCV, Plasma protein, Total WBC count, Blood smear examination, Differential WBC count, RBC/leukocyte morphology, Reticulocyte count (if anemic), Hemoglobin concentration, Erythrocyte indices.

Packed Cell Volume (PCV)

  • Percentage of whole blood composed of RBCs.

  • Layers after centrifugation: RBCs, Buffy coat (WBCs/platelets), Plasma.

  • Plasma appearance: Clear to pale yellow (normal), Cloudy (lipemic), Reddish tinge (hemolyzed), Deep yellow (icteric).

  • Significance: Below normal = Anemia/inadequate blood volume; Above normal = Polycythemia/dehydration.

Plasma Protein Concentration

  • Measured from plasma using a refractometer (g/dL); lipemic samples cause false increases.

Hemoglobin Testing

  • Functional unit of RBC, transports oxygen.

  • Heme portion contains iron, globin portion contains amino acids.

  • Forms: Oxyhemoglobin, Methemoglobin, Sulfhemoglobin.

Erythrocyte Indices

  • Help classify anemia by objective measures of RBC size and hemoglobin concentration.

  • Mean Corpuscular Volume (MCV): Average RBC size. MCV=(PCV÷RBC)×10 fLMCV = (PCV \div RBC) \times 10 \text{ fL}.

  • Mean Corpuscular Hemoglobin (MCH): Mean weight of hemoglobin per RBC. MCH=(Hemoglobin÷RBC)×10 pgMCH = (Hemoglobin \div RBC) \times 10 \text{ pg}.

  • Mean Corpuscular Hemoglobin Concentration (MCHC): Hemoglobin concentration per RBC. MCHC=(Hemoglobin÷PCV)×100 g/dLMCHC = (Hemoglobin \div PCV) \times 100 \text{ g/dL}.

Reticulocyte Counts

  • Percentage of immature RBCs; performed on anemic patients to assess bone marrow response.

  • Evaluated by automated laser-based methods or manually using supravital stains (e.g., New Methylene Blue).

  • Cats: Count aggregate reticulocytes (large clumps of reticulum); do NOT count punctate (2-8 small granules).

  • Calculation: (\text{Number of Reticulocytes Counted} \div 1000 \text{ RBCs}) \times 100 \text{%}.

  • Corrected Reticulocyte Count (CRC): Adjusts for patient's anemia. CRC = \text{Observed Reticulocyte %} \times (\text{Patient's PCV} \div \text{Normal PCV for species}).

Hematologic Abnormalities & Bone Marrow Terminology

  • Classified by cell number (hypercellular, hypocellular, aplastic) and morphology.

  • Aplasia: Less than 25% myeloid cells.

  • Myelofibrosis: Increased fibrous tissue displacing hematopoietic tissue.

  • Neoplasia (Leukemia): Predominance (>30%) blast cells in bone marrow.

Anemia Classifications

  • By Bone Marrow Response:

    • Regenerative: Bone marrow responds with increased reticulocytes (except horses).

    • Nonregenerative: Bone marrow unable to respond (reticulocytes absent, e.g., iron deficiency, drug toxicity).

  • By RBC Size (MCV):

    • Normocytic: Normal size RBCs.

    • Macrocytic: Large RBCs (transitory in regenerative anemia).

    • Microcytic: Small RBCs (e.g., iron deficiency).

  • By Hemoglobin Concentration (MCHC):

    • Hypochromic: Reduced hemoglobin, pale central region (e.g., iron deficiency).

    • Normochromic: Normal hemoglobin levels.

    • Hyperchromatic: Not possible.

  • By Etiology: Hemolytic (RBC destruction), Hemorrhagic (blood loss), Iron Deficiency, Production Disorders (reduced/defective erythropoiesis).

Morphologic Changes of Blood Cells

  • Quantification: Scale of 1+ (5-10%) to 4+ (>75%) OR Slight (10%), Moderate (25%), Marked (50%).

White Blood Cell Abnormalities

  • Nuclear: Pelger-Huet anomaly (hyposegmentation), Nuclear hypersegmentation (>5 lobes).

  • Cytoplasmic: Toxic change (basophilia, Döhle bodies, toxic granulation), Intracytoplasmic inclusions (e.g., Ehrlichia morulae), Atypical and Reactive lymphocytes, Lysosomal storage disorders, Birman cat neutrophil granulation, Chédiak-Higashi syndrome (fused lysosomes).

  • Degenerative: Smudge cells (ruptured leukocytes), Karyolysis (nuclear dissolution), Pyknosis (nuclear condensing), Karyorrhexis (nuclear fragmentation).

  • Inclusions: Siderotic granules (in neutrophils/monocytes).

Red Blood Cell Abnormalities

  • Arrangement: Rouleaux (stacking, disperses in saline), Autoagglutination (clumping, immune-mediated, does NOT disperse in saline).

  • Size: Anisocytosis (variation in size: macrocytes, microcytes).

  • Color: Polychromasia (bluish tint, young cells), Hypochromasia (decreased color, pale central region), Hyperchromatophilic (darkly stained, not true oversaturation).

  • Shape (Poikilocytes): General term for abnormally shaped cells.

    • Specific types: Schistocytes (fragments), Acanthocytes (spur cells), Echinocytes (burr cells/crenated), Drepanocytes (sickle cells), Keratocytes (helmet/blister cells), Spherocytes (small, dark, no central pallor - immune-mediated hemolytic anemia).

    • Also: Leptocytes (target/codocytes), Stomatocytes (folded cells), Elliptocytes (ovalocytes), Eccentrocytes (hemoglobin pushed to one side), Dacryocytes (teardrop shaped).

  • Inclusions: Basophilic stippling (residual RNA), Howell-Jolly bodies (nuclear remnants), Heinz bodies (denatured hemoglobin, normal up to 5% in cats), Nucleated erythrocytes (immature cells).

  • Parasites: Mycoplasma haemofelis, Anaplasma, Cytauxzoon, Babesia.