Clinical Pathology - Erythrocyte (RBC) Disorders: Polycythemia and Anemia

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What is polycythemia characterized by?

an increase in PCV, Hb concentration and/or RBC count

What type of polycythemia is most commonly seen in veterinary medicine?

relative

What can cause relative polycythemia?

dehydration, exercise, fear or excitement

What is absolute polycythemia?

a real increase in RBCs

What laboratory values will show a relative polycythemia?

an increase in total protein and albumin

What laboratory values will show an absolute polycythemia secondary to chronic hypoxia?

a decrease in arterial pO2

What laboratory values will show an absolute polycythemia secondary to renal tumors or cysts?

increased erythropoietin

What laboratory values will show polycythemia vera (a primary absolute polycythemia)?

decreased erythropoietin

What is anemia characterized by?

a decrease in PCV, Hb concentration and/or RBC count

What are the clinical implications of anemia?

inadequate tissue oxygenation (pale mucous membranes, weakness, inappetance, anorexia and syncope) and compensatory mechanisms (tachypnea and tachycardia)

What are some signs which may be associated with causes of anemia?

icterus, bleeding, fever or splenomegaly

What is regenerative anemia characterized by?

an increase in the number of reticulocytes produced by the bone marrow to compensate for the anemia

What are some laboratory signs of regenerative anemia?

reticulocytosis (increased MCV and RDW), macrocytosis, hypochromasia (decreased MCHC); in blood smears - polychromasia and anisocytosis; nucleated RBCs; Holly-Jolly bodies; basophilic stippling; leukocytosis and increased platelets

What happens in hemorrhagic anemia?

RBCs and plasma proteins are lost together; at first PCV and TPP are normal after bleeding but as fluid shifts from extravascular space into the intravascular space or IV fluids are given, dilution causes PCV and TPP to drop

What are the causes of acute blood loss (hemorrhagic anemia)?

trauma, surgery, coagulation disorders, GI hemorrhage secondary to ulcers, hemangiosarcoma, hookworks and external parasites

In many cases, signs of RBC regeneration are present in blood but progressive depletion of iron stores may produce iron deficiency anemia characterized by what?

normo to microcytosis, hypochromasia, increased platelet count and a decrease in reticulocytes

What can cause chronic blood loss?

gastrointestinal tumors (internal), parasites (internal and external) and hemangiosarcoma

What can be seen (laboratory) with hemolytic anemia?

increased or normal plasma total protein; plasma can be icteric or hemolysed; urine may be red due to hemoglobin; abnormal erythrocyte morphology

What can be used to differentiate hemolysis and hemorrhage?

TPP and plasma color

What are the clinical signs associated with an increase in hemoglobin catabolism?

hemoglobinemia and hemoglobinuria; icterus

Red blood cell lysis may occur by what two mechanisms?

intravascular hemolysis and extravascular hemolysis

What can cause intravascular hemolysis?

parasites/infectious causes; vascular endothelial lesions; oxidant damage; poisoning with Cu and Zn; genetic disorders; severe hypophosphatemia

What are the laboratory findings with intravascular hemolysis?

decreased PCV, TPP increased or normal and icteric or hemolysed plasma

What is immune mediated hemolytic anemia?

when autoantibodies are produced against "normal" erythrocytes that are phagocytosed by the spleen

What causes the appearance of abnormal antigens on the erythrocyte cell membrane?

immune-mediated hemolytic anemia

What are the laboratory findings with immune-mediated hemolytic anemia?

decreased PCV, normal or increased TPP, yellow colored plasma, spherocytosis and autoagglutination

What are additional tests to characterize immune-mediated hemolytic anemia?

coombs test and erythrocyte fragility test

What does the Coombs test detect?

antibodies directed at the erythrocyte membrane

What can cause false positive of the Coombs test?

chronic infections; parasites; drugs; neoplasms

What can cause false negatives of the Coombs test?

inadequate antibody production

When is the Coombs test not needed?

if autoagglutination is occurring - it will be positive

What is non-regenerative anemia characterized by?

an absence of/reduction in reticulocyte response in an anemic animal

A non-regenerative anemia will produce what?

a normocytic-normochromic anemia (MCV, RDW, and MCHC are all within the reference ranges); in blood smears there will be absence of polychromasia and anisocytosis

What primary bone marrow disorders can cause non-regenerative anemia?

some myeloproliferative, lymphoproliferative and myelodysplastic disorders, viruses (FelV and canine parvovirus), and some drugs (estrogens, immunosuppressive agents and NSAIDs)

What secondary bone marrow disorders can cause non-regenerative anemia?

chronic inflammatory disease, chronic renal failure with decreased erythropoietin levels, and some endocrine disorders such as hypothyroidism and hypoadrenocorticism

What is a very common cause of mild anemias?

chronic inflammation

During chronic inflammation, what does the body sequester as a defense mechanism?

iron

What are the laboratory findings of non-regenerative anemia?

decreased PCV and absent/reduced signs of RBC regeneration (reticulocytes)
-primary: diagnosis by bone marrow evaluation; leukopenia and thrombocytopenia may occur
-secondary: laboratory findings of the primary disease

A macrocytic-hypochromic anemia is characterized as what?

regenerative

A normocytic-normochromic anemia is characterized as what?

non-regenerative; could be regenerative (base off of the reticulocyte count)

A microcytic-hypochromic/normochromic anemia is characterized as what?

iron deficiency

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