ANEMIA

4 ANEMIA



Shannon Jones Hostetter, Claire B. Andreasen



1 Define anemia and explain the difference between relative anemia and absolute anemia.


Anemia is defined as a decrease in the hematocrit, erythrocyte count, and hemoglobin concentration. Relative anemia is not associated with a true reduction in the total red blood cell (RBC) mass, but rather is caused by a dilutional effect that can be observed after aggressive fluid therapy or other cause of increased plasma volume. Absolute anemia is considered an actual reduction in the total RBC mass.



2 What parameters are used to classify anemias in dogs and cats?


The various RBC indices, including mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and red cell distribution width (RDW) (see Chapter 3), are useful in classifying anemias as either regenerative or nonregenerative. Also, both reticulocyte count and RBC morphology are extremely important in determining if an anemia is regenerative or nonregenerative.



3 Identify some common causes of nonregenerative anemia.



a. Blood loss of less than 3 days (a regenerative anemia that has not yet had time to show a regenerative response)

b. Erythropoietic suppression
(1) Anemia of chronic disease (anemia of inflammatory disease)

(2) Renal failure

(3) Metabolic disease

(4) Drugs and toxins

c. Infections (e.g., parvoviruses)

d. Bone marrow disease:
(1) Myelofibrosis

(2) Pure red cell aplasia

(3) Marrow necrosis

(4) Neoplasia

e. Radiation


4 List the two major categories of regenerative anemia and give examples of each.



Hemorrhage



a. Acute blood loss of greater than 3 days’ duration

b. Some cases of shorter term chronic blood loss anemia (but if iron deficiency develops or if a concurrent disease blunts the regenerative response, then there can be a nonregenerative anemia)


Hemolysis



a. Pyruvate kinase (PK) deficiency

b. Phosphofructokinase (PFK) deficiency

c. Immune-mediated hemolytic anemia

d. Infection-associated hemolysis (e.g., erythrocyte parasites, some bacteria)

e. Chemical/toxin-induced hemolytic anemia

f. Microangiopathic hemolytic anemia


5 Describe the characteristics of anemia from acute blood loss.



a. After acute hemorrhage, hematocrit initially is within the normal reference interval because both cellular components and plasma are lost in equal amounts. The body begins to replace plasma volume a few hours after blood loss, with total replacement of plasma volume in 2 to 3 days. Hematocrit begins to drop as plasma volume is restored as a result of hemodilution.

b. Polychromasia is an indicator of increased bone marrow production of erythrocytes and is observed within 2 to 3 days after acute blood loss.

c. Reticulocytosis is observed within 2 to 3 days of acute blood loss unless suppressed by another concurrent disease.


6 Approximately how long does it take for the hemogram to return to normal after an acute, finite period of blood loss in the dog?


It takes approximately 1 to 2 weeks for the hemogram to return to reference intervals in the dog.



7 What are the characteristics of anemia secondary to chronic blood loss?



a. Regenerative progressing to nonregenerative anemia: the anemia becomes nonregenerative as iron stores are used up leading to an iron deficiency anemia with time. This anemia is generally not as pronounced as that seen with acute blood loss.

b. Iron deficiency anemia: can develop secondary to prolonged hemorrhage.


8 What is the most reliable laboratory indicator of regenerative anemia in dogs and cats?


An absolute increase in reticulocyte numbers is the best indicator of a regenerative bone marrow response to anemia.



9 List the common erythrocyte changes that indicate a regenerative anemia.



a. Reticulocytosis

b. Polychromasia

c. Anisocytosis/increased RDW

d. Macrocytosis/hypochromasia due to reticulocytosis


10 Define extravascular hemolysis, and list common causes of extravascular hemolysis in the dog and cat.


Extravascular hemolysis is the removal and subsequent breakdown of erythrocytes by macrophages within the spleen and liver.


Causes of extravascular hemolysis include reduced RBC deformability, antibody or complement-mediated phagocytosis, hypersplenism, and altered cytoplasmic adenosine triphosphate (ATP) content.



11 What is intravascular hemolysis, and what are at least four mechanisms of this disorder in the dog and cat?


Intravascular hemolysis is the rupture of erythrocytes within the vascular system.


Mechanisms for intravascular hemolysis include the following:


a. Oxidative injury

b. Membrane alteration

c. Physical damage

d. Immune-mediated lysis

e. Parasitism (e.g., babesiosis) (Figure 4-1)

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Aug 26, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on ANEMIA

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