Erythrocyte Indices, Morphology, and Inclusions

Comprehensive vocabulary flashcards covering erythrocyte indices, reticulocyte counting procedures, red blood cell inclusions, and abnormal erythrocyte morphologies based on veterinary hematology lecture slides.

Anemia

A condition characterized by a lack of functional red blood cells (RBCs) or hemoglobin, resulting in a low packed cell volume (PCV).

Erythrocyte indices

Parameters calculated by an automated machine or manually—including MCV, MCH, and MCHC—that help differentiate types of anemia.

Mean Corpuscular Volume (MCV)

An erythrocyte index representing the average size of red blood cells, calculated as $\frac{\text{PCV}}{\text{RBC count}} \times 10$ and expressed in femtoliters ($\text{fl}$ or $\text{fL}$).

Femtoliter (fL)

A unit of volume equal to $10^{-15}\,\text{liters}$, utilized as the unit of measurement for Mean Corpuscular Volume (MCV).

Macrocytosis

An erythrocyte population characterized by a Mean Corpuscular Volume (MCV) that is above normal reference limits.

Microcytosis

An erythrocyte population characterized by a Mean Corpuscular Volume (MCV) that is below normal reference limits.

Normal MCV reference intervals (canine and feline)

$60\text{--}77\,\text{fl}$ in dogs and $39\text{--}55\,\text{fl}$ in cats.

Mean Corpuscular Hemoglobin Concentration (MCHC)

An erythrocyte index that evaluates cellular hemoglobin concentration relative to packed cell volume, calculated as $\frac{\text{Hemoglobin}}{\text{PCV}} \times 100$.

Normochromic

A state in which red blood cells possess a normal concentration of hemoglobin, yielding an MCHC value within reference limits (e.g., $33.33\,\text{gm/dl}$).

Hypochromic

A state in which red blood cells possess a reduced concentration of hemoglobin, yielding a low MCHC value (e.g., $26.66\,\text{gm/dl}$), which is usually associated with blood loss.

Reticulocyte

An immature red blood cell whose rough endoplasmic reticulum (ER) and ribosomes stain with new methylene blue (NMB); normally constitutes approximately $1\%$ of circulating RBCs in dogs and increases in regenerative (responsive) anemias.

Supravital stain (NMB)

New methylene blue; a stain applied to living, unfixed cells that interacts intracellularly to precipitate and stain ribosomal RNA in reticulocytes.

Polychromatophil

An immature red blood cell observed on a routine Diff-Quik or Wright-stained blood film; stains bluish-red due to residual RNA in an already fixed (dead) cell.

Reticulocyte vs. polychromatophil staining

Comparison demonstrating that live cells stained with NMB reveal precipitated ribosomal RNA networks (reticulocytes), whereas fixed dead cells stained with Diff-Quik display diffuse bluish-red cytoplasm (polychromatophils).

Species variations in circulating reticulocytes

Immature RBCs that increase in dogs and cats during regenerative anemias, are normally present in ruminants, and are never seen in the peripheral blood of horses.

Feline reticulocyte forms

Aggregate reticulocytes (large clumps of reticulum, which are the ones counted during a reticulocyte count) and punctate reticulocytes (individual small dots of reticulum).

Monolayer field estimation for reticulocyte count

A procedure where total RBCs are counted in one oil-immersion monolayer field, $1000$ is divided by that count to determine the necessary number of fields, and only reticulocytes are counted across that calculated number of fields.

Observed reticulocyte percentage formula

The calculation used to convert the total reticulocytes counted per $1000$ RBCs into a percentage (per $100$ cells): $\frac{\text{reticulocytes in } 1000\text{ RBCs}}{10} = \text{observed \%}$.

Basophilic stippling

The presence of multiple small blue dots within red blood cells stained with Diff-Quik, representing clumped residual ribosomal RNA in fixed (dead) cells; commonly seen in immature RBCs of ruminants and regenerative anemias in cats.

Lead poisoning in dogs (blood smear indicator)

A toxic condition characterized by basophilic stippling in canine erythrocytes, especially when nucleated red blood cells (nRBCs) are also present without significant anemia.

Metarubricytes (nRBCs)

Nucleated red blood cells with cytoplasm varying from blue to red, commonly observed in responsive anemias and occasionally in normal animals.

Corrected WBC count formula

A calculation performed when metarubricytes (nRBCs) are present on a blood film: $\frac{100\,\text{WBCs}}{100 + \#\,\text{nRBCs}} \times \text{WBC count}$.

Howell-Jolly bodies

Common, non-abnormal round nuclear remnants seen in young erythrocytes, appearing as a single blue dot anywhere within the cell; must not be confused with blood parasites.

Heinz body

A bleb on the outer edge of a red blood cell formed by denatured hemoglobin; appears refractile with Diff-Quik stain and blue with new methylene blue (NMB) stain.

Etiologies of Heinz bodies

Substances causing denatured hemoglobin inclusions, including onion, garlic, propofol, propylene glycol, NMB stain, and acetaminophen (commonly seen in cats, abnormal in other species).

Canine Distemper inclusion bodies

Uncommon viral inclusion bodies that vary in size from cell to cell and may be identified in red blood cells, white blood cells, or squamous epithelial cells.

Keratocyte

An abnormally shaped red blood cell resulting from ruptured membrane vacuoles, presenting either as a 'blister cell' or a 'helmet cell' with horn-like projections.

Dacryocytes

Teardrop-shaped red blood cells observed in myelofibrosis and certain other myeloproliferative diseases; can appear as an artifact if all cell tails are pointed in the same direction.

Stomatocytes

Erythrocytes with an oval-shaped, slit-like area of central pallor resembling a mouth (stoma); associated with membrane defects, hereditary stomatocytosis in Alaskan Malamutes and Miniature Schnauzers, or preparation artifact.

Leptocytes

Thin red blood cells with an increased membrane-to-volume ratio that may appear as target cells (codocytes) or folded cells, and can also be produced as an artifact.