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To see what normal blood and urine values are, go here
For an explanation of causes of most abnormal blood and urine tests, go here
To see how tests are grouped, go here
When your dog or cat’s blood is drawn up into a thin glass tube and then spun in a centrifuge, the height of the column of red cells that were spun to the bottom is its hematocrit.
Normally, about half of the tube then consists of the pet’s straw-colored blood serum at the top, with packed red blood cells at the bottom. If the red lower portion is anything less than about 40% of the total, your pet is anemic. The next test, hemoglobin, measures the actual amount of the blood carrying element, hemoglobin, in your pet’s blood. Low hematocrits almost always lead to low hemoglobin levels. The only exception is when the fewer-than-normal red blood cells are larger than normal (a macrocytic MCV).
All causes of anemia including, hemorrhage into the intestinal tract (such as due to parvovirus infection in dogs or coccidiosis infection in kittens), blood sucking parasites such as hookworms, heavy flea infestation, blood loss from wounds or blood leakage within the body after trauma.
Blood parasites (such as hemobartonella/mycoplasmosis in cats, babesiosis in dogs) and Ehrlichia (ehrlichiosis/ anaplasmosis) in cats can be responsible for a low hematocrit.
Autoimmune anemias, where red blood cells are destroyed by the pet's own body is another fairly common cause in dogs.
Rupture of a major blood vessel, toxic bone marrow suppression and bone marrow tumors can also lower your pet's Hct.
In older pets, chronic kidney disease is a very common cause of anemia. Chronic liver disease, malnutrition and vitamin/mineral deficiencies (B12, Iron, folate) can cause low Hct as well. Vitamin B12 (cobalamin) can also be reduced in pets with chronic intestinal inflammation (IBD, Triad disease, lymphoma syndromes) leading to anemia.
Heavy tick infestation can also cause anemia and a low Hct. But anemia is those pets is more likely to be caused by the blood parasites those ticks carry or the general stress that animals living in sub-standard conditions endure.
The most common cause is dehydration. Diarrhea and vomiting are the most common causes of dehydration in dogs and cats - particularly immature ones - but a lack of interest in drinking, diuretic medications such as furosemide can cause dehydration as well.
On very rare occasions, your pet could actually be producing too many red blood cells. This rare condition can occur when kidney tumors produce erythropoietin (a stimulant to RBC production) or due to unknown causes.
It is normal for greyhound dogs (and perhaps other sight hounds (ref) ) to have high hematocrits. It can also be a response to living at high altitudes or chronic lung disease, both of which limit your pet's available oxygen.