Anemia Flashcards
a rational approach to anemia
Explain why anemia tends to be common in cats
Anemia tends to be common in cats because:
- The lifespan of feline red blood cells is quite short (70 days versus 110 days for canine RBCs)
- The blood volume (and consequently the RBC mass) of a cat (60-70 ml/kg) is less than that of the dog (80-90 ml/kg) - Cats develop oxidative damage to hemoglobin more readily, which further contributes to the reduced RBC lifespan
Explain why cats may be severely anemic before clinical signs develop (especially if the disease is chronic)
The hemoglobin in feline RBCs has a relatively low affinity with oxygen, which means that it releases oxygen quite readily in tissues
Therefore, cats can tolerate low hemoglobin levels and may actually be severely anemic before clinical signs develop
What physiopatholical mechanism explain the clinical signs of anemia
The clinical signs of anemia are due to both tissue hypoxia and the body’s compensatory mechanisms to counteract this (by increasing cardiac output)
The number and severity of signs depend on the degree and chronicity of anemia
What are the main signs of anemia
Gum pallor
Weakness/lethargy
Dyspnoea/tachypnoea
Tachycardia
Hemic heart murmur
How is the severity of anemia classified
Mild: PCV 20-26%
Moderate: PCV 14-19%
Severe: PCV 10-13%
Very severe: PCV < 10%
It is important to assess the severity of anemia after any volume depletion has been corrected with fluid therapy
Furthermore, severity of anemia at presentation is not predictive of survival
What are the three basic mechanisms leading to anemia
Anemia can be caused by three basic mechanisms:
- hemorrhage (internal or external blood loss)
- hemolysis (increased RBC breakdown) - decreased RBC production
Give some examples for each pathophysiological cause of anemia
Hemorrhage
- vessel wall damage
- cooagulopathy
Increased RBC destruction
- Intravascular hemolysis
- Extravascular hemolysis
- Combination
Decreased production
- Bone marrow disease (toxicity, dysplasia, neoplasia)
- Lack of stimulation (erythropoietin deficiency)
- Anemia of chronic and/or inflammatory disease
- Iron deficiency
How would you determine the basic category of anemia
Step 1: establish whether the anemia is regenerative or non-regenerative
- Theoretical results:
- non-regenerative = decreased production
- regenerative = hemolysis or hemorrhage
Step 2: look at the serum protein levels
- Theoretical results:
- normal to high = hemolysis
- low = hemorrhage
What is an important differential for non-regenrative anemia
It is important to establish whether the anemia is truly non-regenerative or only pre-regenerative
- the bone marrow can take up to 3-5 days after hemolysis or hemorrhage to start mount an adequate response
A lack of adequate response can also be because the cat has anemia of chronic disease, or has concurrent renal insufficiency, or is just being poorly responsive
- cats can still have anemia due to hemorrhage or hemolysis even if the anemia is non or poorly responsive
Explain in which circumstances total protein values can be misleading in the classification of anemia
Protein levels can be within the normal range (albeit at the low end) if blood loss is chronic or internal (i.e., into a body cavity) rather than external
- this is especially true if the animal is also dehydrated (and thus relatively hemoconcentrated)
Low protein levels can also be seen with erythroid hypoplasia with concurrent protein losing conditions (e.g., a cat with renal disease in which a lack of EPO may be accompanied by glomerular disease causing excessive protein loss into the urine
- total protein levels may be affected by factors other than the mechanism that is causing the anemia
Give evidence of a regenerative response
Evidence of regeneration:
- Presence of polychromatophilic erythrocytes
- Increased absolute reticulocyte count
- Increased mean corpuscular volume (MCV) - not always present
Explain why Diff-Quick staining is not the best to evaluate regeneration on a blood smear
Polychromatophilic erythrocytes are young RBCs identified on a blood smear by their large size and pale blue-grey appearance
- Diff-Quick do not reveal polychromasia well
Diff-Quick staining also cannot differentiate between the different types of feline reticulocytes (older “punctuate” reticulocytes versus the younger “aggregate” reticulocytes)
Explain the difference between the two types of reticulocytes and how reticulocyte count is established
The reticulocyte count is usually assessed manually on new methylene blue-stained blood smears or by some analyzers
Aggregate reticulocytes
- they contain medium to large clumps of darkly staining polyribosomes
- they mature into the punctuate form after about 12 hours in the circulation
- they are released from the bone marrow within 24-48 hours after acute hemorrhage or hemolysis
- their numbers reach a peak by 4-6 days then gradually decline by 9-13 days
Punctate reticulocytes
- they contain small darkly staining clumps of polyribosomes
- they tend to be more numerous as they tend to persist for about 10 days before maturing into erythrocytes
- their numbers peak at 9-13 days then gradually decline
How can you classify the regenerative character of the anemia according to the reticulocyte count
The reticulocyte count should ideally be corrected for the level of anemia, using the following formula:
Corrected reticulocyte count (%) = observed reticulocyte count * (patient PCV/0.37)
A corrected reticulocyte count of greater than 1% is indicative of a regenerative response in the cat
Classify the regenerative response of an anemia according the absolute aggregate reticulocyte count
Mild: 50,000 - 100,000
Moderate: 100,000 - 200,000
Marked: > 200,000
