Evaluation of Erythrocytes: RBC Indices Flashcards
MCV
mean cell volume
uses erythrocyte population histogram and/or calculation - check with film!
MCH
mean cell hemoglobin, determined by calculation, depends on erythrocyte size and internal hemoglobin concentration
NOT GENERALLY USEFUL
MCHC
mean cell hemoglobin concentration
determined by cacluclation
use of electronically determined HCT makes it less precise
RDW
red cell distribution width
coefficient of variation of erythrocyte volumes and an electronic measure of anisocytosis
MCV increases _______ (slower/faster) than reticulocyte counts in response to hemolytic anemia.
slower
What is spurious macrocytosis? What causes it?
autoagglutination of erythrocytes
caused by: prolonged blood storage before assay, persistent hypernatremia (dogs and cats), hypothalamic lesion
Reasons for seeing microcytosis in animals
- chronic iron deficiency anemia
- portosystemic shunts, primarily in dogs
- anemia of inflammatory disease
- cats with hepatic lipidosis
- japanese breed dogs (akita and shiba) w/o anemia
- inhibitors of heme synthesis (ie. lead and chloramphenicol toxicity, vitamin B6 deficiency)
- storage iron depletion from increased erythropoiesis
- copper deficiency
- myeloproliferative disorders
- familial dyserythropoiesis in English Springers
- Herditary elliptocytosis
What does a high MCHC value indicate?
- NOTHING.
- no such thing as “hyperchromic” - always an artifact
- intravascular hemolysis
- in vitro hemolysis
- treatment with cross-linked Hb
- Heinz bodies in RBCs
- lipemia
- erythrocyte agglutination in electronic cell counters
What do low MCHC values indicate?
regenerative anemias, especially when high numbers of reticulocytes are present
chronic iron deficiency anemia
hereditary stomatocytosis in dogs
abyssinian and somali cats with erythrocyte osmotic fragility
spurious in some dogs and cats with persistent hypernatremia
What does an increased RDW indicate?
- anemias with increased numbers of large reticulocytes
- iron deficiency anemia with increased number of microcytes
- erythrocyte fragmentation
- after blood transfusion - different sized cells
- dyserythropoiesis
- hereditary stomatocytosis
- spuriously increased - platelets counted, agglutination etc.
What situations cause increased/decreased serum iron concentrations?
increased: hemolytic anemia, glucocorticoids in dogs and horses
decreased: iron deficiency, anemia due to inflammatory dz, portosystemic shunts, glucocorticoids in cattle
What does serum ferritin concentration correlate with? What does an increase/decrease tell you?
correlates with total body iron stores
decreased = iron deficiency
increased = iron overload, hemolytic anemia, inflammation, histiocytic sarcoma complex, transiently in exercising horses
Cyanotic appearing skin tells you…
hypoxemia with low pO2 in arterial blood
methemoglobinemia with normal pO2 in arterial blood
methemoglobin spot test vs. arterial blood gas measurement to determine which
What color is methemoglobin in venous blood?
brown - use spot test to determine
Causes of methemoglobinemia
- administration or consumption of oxidant drugs that can also cause heinz bodies
- acetaminophen, benzocaine, phenazopyridine (dogs and cats)
- copper toxicity (sheep and goats)
- red maple toxicity (horses)
- nitrate toxicity in ruminants
- hereditary erythrocyte methemoglobin reductase deficiency (dogs, cats, horses)
