RBC vocab (clin path)

what is the difference between plasma and serum?

• plasma: liquid from anti-coagulated whole blood

• serum: liquid from coagulated and centrifuged whole blood

mean cell volume (MCV)

average size (volume) of RBCs

• units: femtoliters (fL)

mean cell hemoglobin (MCH)

average amount of hemoglobin/RBC

• units: picograms (pg)

mean cell hemoglobin concentration (MCHC)

• average concentration of hemoglobin/RBC

  • Hb divided by RBC volume

  • units: g/dL

• more diagnostically useful index than MCH

anisocytosis

variation in RBC size that is abnormal for the species

macrocytosis

↑ RBCs with ↑ diameters (correlates with increased MCV)

what is a common cause of macrocytosis?

regenerative anemia (bone marrow releases reticulocytes, which are larger than mature RBCs)

microcytosis

↑ RBCs with ↓ diameters (correlates with decreased MCV)

what are common causes of microcytosis?

• iron deficiency anemia

• porto-vascular anomalies in young dogs (ex. portosystemic shunt)

crenation

• RBC morphology characterized by evenly spaced, blunt projections around the entire surface

• artifact of delayed drying of blood smear on the slide; rarely pathogenic process

poikilocyte

• general term meaning abnormally shaped mature RBC

• includes abnormal shape of central pallor & RBC shape that is not biconcave disc

schistocyte

fragmented RBC usually resulting from shearing injury by RBCs traversing intravascular fibrin deposition or abnormal vessels

acanthocyte

RBC with projections of irregular number, size, and location

what types of disorders are associated with acanthocytes?

• disorders that cause RBC fragmentation

• splenic and hepatic disorders

spherocyte

• spherical RBCs that appear smaller, denser, and lack central pallor (in dogs)

• only reliably detected on canine blood smears; RBCs in other species have little or no visible central pallor

what disorder is associated with spherocytes?

extravascular immune-mediated hemolytic anemia

• (IgG) Ab-coated RBC travels to spleen → splenic macrophage removes Ab and small portion of RBC membrane → RBC reassembles into sphere

eccentrocyte

• RBCs with hemoglobin shifted to one side of the cell

• on the other side, there is a clear area and a thin membrane

• indicates oxidative membrane damage

polychromasia/polychromatophilic RBCs

• describes blue-purple color of reticulocytes on a blood smear stained with Wright’s stain or Diff-quick

  • lack nucleus but retain ribosomes that stain blue & blend with salmon color of hemoglobin

• variable central pallor size/shape or absent

hypochromasia/hypochromia

• microcytic RBCs that are pale with increased central pallor (>1/3 RBC diameter)

• impaired hemoglobin synthesis due to iron deficiency

ghost cells

• RBC membranes with little to no hemoglobin

• primarily associated with intravascular IMHA

  • RBC releases Hb into plasma

nucleated RBCs (nRBC)

• metarubricytes/rubricytes

• normal feature of immature RBCs but usually not in circulation

• (avian/reptile RBCs are nucleated)

appropriate vs. inappropriate metarubricytosis

• appropriate: nRBCs commonly seen in regenerative anemias → not considered pathologic

• inappropriate: nRBCs in the absence of regeneration

  • may be seen with diseases of the spleen and bone marrow & with lead toxicity

howell jolly bodies

• small, round, dark inclusion → nuclear remnant

• eventually removed by spleen (pitting function)

  • more frequent in healthy cats due to poor splenic pitting function

• frequently seen in regenerative anemia

• in the absence of regeneration, may be seen with diseases or absence of the spleen (post-splenectomy)

basophilic stippling

• precipitated ribosomes in immature RBCs (reticulocyte or polychromatophil)

• normal feature of ruminant reticulocytes

• may be seen with regenerative anemia in ruminants; severe regen. anemia in dogs, cats

• pathologically seen with lead toxicity

heinz bodies

• precipitated, denatured “blob” of globin resulting from oxidation of hemoglobin (oxidative damage)

• difficult to see on Wright’s-stained smears; easier to visualize with New Methylene Blue stain

how do domestic species vary in the amounts of reticulocytes released in healthy patients?

• dogs: release some

• cats: release few

• cattle: no reticulocytes in health

• horses: do NOT release reticulocytes in healthy OR anemic states

what are submechanisms of regenerative anemia?

• hemorrhage

• hemolysis

what are submechanisms of nonregenerative anemia?

intra- or extra-marrow disease

ferroportin

iron transporter used to move iron from inside to outside of cells

hepcidin

• acute phase protein that blocks ferroportin → iron accumulates in macrophages → inhibits erythropoiesis during inflammation

• prevent bacteria from stealing and using iron

anemia of inflammatory disease

• infectious & non-infectious inflammation

  • hepcidin released

• usually normocytic, normochromic

  • non-regenerative

• low serum iron → negative acute phase reactant

  • due to sequestration of iron

how does chronic kidney disease cause anemia?

• ↓ production of EPO from renal interstitial fibrosis

• other contributing factors:

  • ↓ response of RBC precursors to EPO

  • ↓ RBC lifespan from circulating wastes

  • mild hemorrhage from gastric mucosal ulcers

how does hypothyroidism cause anemia?

↓ thyroid hormone → ↓ metabolic rate → ↓ O₂ consumption → ↓ EPO → ↓ PCV%

CBC results consistent with intramarrow disease

• unexplained non-regenerative anemia +

  • multiple lineages affected

    • thrombocytopenia

    • leukopenia (neutropenia)

    • lymphocytopenia

  • inappropriate rubricytosis

  • howell-jolly bodies

  • atypical cells

• EXTRA-marrow ruled out

relative erythrocytosis due to dehydration

• most frequent cause of relative erythrocytosis

• no absolute increase in RBC mass

• no increase in EPO

• increase relative to plasma H₂O

relative erythrocytosis due to splenic contraction

• physiologic erythrocytosis mediated by epinephrine — fight or flight response

• horses — large spleen, muscular coat

• increased PCV, no change in [TP]

  • transient redistribution of RBCs

appropriate vs. inappropriate secondary absolute erythrocytosis (↑ EPO)

• appropriate: ↓ pO₂

  • ↑ EPO in response to hypoxemia

• inappropriate: normal pO₂

  • EPO-secreting tumor

  • EPO secretion from focal hypoxic renal tissue

  • rare

primary (absolute) erythrocytosis or polycythemia vera

• bone marrow neoplasm of mature RBCs

• ↑ RBC mass independent of EPO

• primary erythrocytosis: only RBCs increased

• polycythemia vera: other cell lines may also be increased (neutrophils, platelets)

• rare