RBC Morphological variations

Morphology sub-groups

1. Regenerative changes
2. Immune-mediated damage
3. Oxidative injury
4. Membrane / Metabolic disorder
5. Mechanical fragmentation

1) Regenerative Changes

• cells increase in response to anemia

• mostly immature cells that were released into circulation too early

• changes recognized by size/colour variation, more basophilia, nuclear & reticular remnants

Polychromatophil

• regenerative change

• Immature RBCs

• larger than mature RBCs

  • may fold in on itself

  • changes appearance of the center of the cell

    • may also show different types of poikilocytosis (eg. leptocytes)

• Romanowsky-type stains:

  • cytoplasm is bluish-purple

    • due to metabolically active endoplasmic reticulum

Polychromasia grading

+ = 1-5 /100× obj.
++ = 6-10 /100× obj.
+++ = >10 /100× obj.

Reticukocyte

• Polychromatophils are usually reticulocytes, but definitive ID is done under New Methylene Blue stain

• Bluish green in colour

• Visually see the reticulum

  • In cats you must specify granules as:

    • Punctate (dots)

    • Aggregate (lines/clumps)

• regenerative change

Shift RBC

• Polychromatic but also...

• 2× size of a normal RBC

• due to skipped stages in maturation process

• regenerative change

Nucleated RBC

• Rubricyte or metarubricyte

  • Has a nucleus

  • Basophilic cytoplasm

• Cause:

  • Increased demand for cells

  • Mild bone marrow damage

  • Anemia

    • Regenerative = polychromasia

• No anemia, but polychromasia

  • Disease (splenic, lead poisoning)

• regenerative change

Howell-Jolly Body

• Purple circular inclusion obvious within cell

• Nuclear material

• Non-refractile

• During regeneration:

  • Accelerated production

    • macrophages unable to fully remove the nuclei

• Can indicate:

  • RBC production

  • Poorly functioning spleen

  • Bone marrow injury

• regenerative change

Basophilic stippling

• Small variably sized bluish dots (retained RNA)

• Paler & smaller than HJBs

• Romanowsky stain

  • Most noticeable with EDTA

• Causes:

  • Very responsive anemia, esp in bovines

  • Heavy metal poisoning (e.g. lead)

• regenerative change

Anisocytosis (variation in size)

• during regeneration

  • due to presence of larger polychromatophils

• regenerative change

2) Immune-mediated damage

Response to processes in which the RBCs are targeted by the immune system

• WBCs attack the bodys own RBCs

• results in membrane damage with loss of O2 carrying capacity

• causes a severe anemia

  • important to determine cause with anemic samples/patients

Spherocyte

• Hyperchromic & microcytic

  • Decreased size but...

  • Normal volume

• WBC (macrophage) damages cell membrane

  • Less surface area for gas exchange

  • Loses discoid shape

    • now spherical

    • lacking central pallor

• secondary to RBC fragmentation

• Most easily identified in dogs

• immune-mediated damage

agglutination

• Clumping of RBCs

  • like a bunch of grapes

  • Cross-linked surface antibodies

• Macroscopic:

  • Seen in vacutainer (grainy)

  • Seen on the slide

• Microscopic:

  • Differentiate from rouleaux:

    • Saline agglutination test

• No automated counters (will clog)

• immune mediate damage

Ghost cell

• Post-intravascular lysis

• membrane remains largely intact, but empty

• immune mediated damage

3) Oxidative injury

Hemoglobin in the RBC is oxidized (rusted) and denatured

leads to less function hemoglobin available to carry O2

Occurs in specific disease states + / - drug interactions

erythrocyte refractile body (when romanowsky type stain is used)

• Not commonly seen except in cats (up to 10%)

• Refractile ‘blebs’ on membrane edge

• Dissolve in methanol/ethanol

• Drug/toxin causes:

  • Acetaminophen

  • Urinary acidifiers

  • Aquarium products (cats)

  • Onions & related (dogs,cats,cows...)

• Disease causes:

  • Metabolic (diabetes mellitus)

  • Renal disease

  • Lymphosarcoma

• oxidative injury

ER body / heinz body

• Termed a Heinz Body when stained with New Methylene Blue stain

• Most people use the term ‘Heinz Body’ for both

• May be single, multiple, bulging

• Look like pompoms on a toque or a blob of ketchup on cell’s edge

• oxidative injury

Eccentrocyte

• Inner cell membrane is fused to outer edge, loss of central pallor

• Oxidant exposure from:

• Onions

• Acetaminophen

• Vitamin K

• More common in dogs

• oxidative injury

Keratocyte/blister cell

• Localized area of membrane damage from:

  • Fibrin strands in vasculature

  • Oxidative injury

  • Inflammation

• look a bit like a handbag

• oxidative injury

Keratocyte: Bite cell or apple stem cell or helmet cell

• 2 fairly uniform projections or one larger projection

• appear like a ruptured “blister”

• oxidative injury or mechanical damage

Membrane/metabolic disorders

Primarily shape variations that affect ideal o2 carrying capacity of the RBCs

Result of environmental exposure, both in vivo and in vitro to:

• other blood components or lack thereof in disease state

• certain drugs, gases, toxins

• + / - artifact from handling post-sampling

Echinocyte

• in vivo (in the body) crenation

• short spines distributed evenly, like an echidna

• True echinocytes in:

  • Renal disease

  • Lymphosarcoma

  • Rattlesnake venom

  • Absolute dehydration

• metabolic/membrane disorder

Crenation

• False echinocyte

• In vitro artifact

  • Most commonly from

    • slow air-drying

    • prolonged time in EDTA before making a slide

• All cells in one field of view must be crenated to consider that crenation is present

• metabolic/membrane disorder

Burr cell

• Similar to echinocyte, but

  • Oval to elongate

• Often due to renal disease

• metabolic/membrane disorder

Acanthocyte (spur cell)

• Membrane abnormality

  • 2 or more blunt, finger-like projections (longer than echinocyte spines)

• Alteration in cholesterol concentration

  • Cholesterol : phospholipid ratio

  • Excess cell membrane

• Disease:

  • Liver (severe)

  • Renal

  • Hemangiosarcoma

• metabolic/membrane disorder

sickle cell

• Occasionally normal in sheep

• Normal in deer when exposed to O2 (collection)

• (inherited disorder in humans)

• The dangers:

  • Cells are not pliable

  • Cells are sticky

    • Block blood flow

• metabolic/membrane disorder

Hypochromasia

• Normal to microcytic

• Decreased hemoglobin

  • Increased area of central pallor, thin outer rim

  • Gradual colour transition from thin outer rim to pallor

    • Differentiate from torocytes

• Commonly from mineral or nutrient deficiency

  • Most common: iron deficiency

• metabolic/membrane disorder (change in central pallor)

Leptocytes

• General term for:

  • Larger RBC

  • Thin cell membrane

    • Excess membrane folds easily

• increased surface area : volume

• often polychromatophils as well; assess both things

• Includes these sub-types:

  • Torocyte

  • Stomatocyte

  • Codocyte

  • Bar cell

• metabolic/membrane disorder (change in central pallor)

Leptocyte: Torocyte

• “Punched-out” cell

• Accentuated central pallor

  • Abrupt colour transition from outside (normal) to centre (colourless)

• Smaller area of CP than hypochromic cells

• Usually artifact, from

  • slow air-drying; margination of hemoglobin; prolonged contact with EDTA or insufficient sample mixed with EDTA

• Not diagnostically significant

• metabolic/membrane disorder (change in central pallor)

Leptocytes: Stomatocytes

• Central pallor appears oval or elongated (like a mouth)

  • RBC membrane metabolic defects (hereditary), or

  • Preparation artifact from blood film preparation

    • smear too thick,

    • drying time

    • increased pressure

• metabolic/membrane disorder (change in central pallor)

Leptocytes: Codocytes (target cells)

• Bulls-eye appearance

• cells have excess membrane or low iron

  • iron-deficiency anemia

  • severe liver disease affecting cholesterol : phospholipid ratio of membrane

• PCV & MCHC help determine cause

• only visualized in canines

• metabolic/membrane disorders (Change in central pallor)

Leptocytes: bar cells

• Also called a “Knizocyte”

• Similar to Codocyte / Target cell in cause and determination

• Appear to have a bar across central pallor

• metabolic/membrane disorders (change in central pallor)

Elliptocytes (ovalocyte)

• Oval cells

• Oval central pallor

• RBC membrane defects from certain inherited disorders or drugs

• normal in camelids

• metabolic/membrane disorder (change in central pallor)

5) Mechanical Damage

Physical damage during circulation from “functional” parts of circulation:

• heart valves

• fibrin strands

• platelet aggregation

• thromosis

occurs when these incidents increase significantly in certain disease states

Schistocyte (or Schizocyte)

• Varied sizes and shapes

• Microvascular abnormalities due to shearing

  • DIC (clotting disorder)

  • Heartworm

  • Hemangiosarcoma

  • CHF

  • IMHA

• mechanical damage/fragmentation

Keratocyte/blister cell

• Localized area of membrane damage from:

• Fibrin strands in vasculature

• Oxidative injury

• increased in inflammation

• mechanical damage or oxidative injury

Dacryocyte

• Teardrop shape

• Failure to return to natural shape after moving through capillaries

• “Pitting” function of spleen

• Not hugely significant

• Distinguish from preparation artifact! How?

  • Artifact when:

    • in feathered edge, or

    • all pointing in one direction

• mechanical damage/fragmentation