Hematocrit (HCT, PCV) in cats and dogs
Hematocrit is the share of blood volume taken up by red blood cells. It is the number vets use most to decide whether an animal is anemic. A low value points to anemia; a high one most often means the blood is concentrated by dehydration.
What it shows
The same idea is measured in two ways, and forms label them differently:
- HCT (hematocrit) is calculated by the analyzer: it multiplies the average red cell size (MCV) by the red cell count (RBC).
- PCV (packed cell volume) is measured directly: blood in a thin tube is spun in a centrifuge, and the height of the red cell column is read against the whole column. eClinPath calls it the quickest and most readily available measure of red cells.
Usually the two agree, but they make different mistakes. HCT inherits every error of MCV and RBC: if red cells swell while the sample waits, MCV and HCT both rise. PCV depends on how well cells pack in the tube and on how long the tube was spun. So when you compare a series, it helps to know which of the two each form reports.
Higher than reference — what it may be a sign of
- Dehydration — a frequent reason: the blood loses water and red cells become relatively concentrated.
- Breed: dachshunds, greyhounds and whippets have higher values with healthy blood; eClinPath gives an average of about 59% in adult greyhounds.
- True erythrocytosis: the body really makes too many red cells — driven by the hormone erythropoietin, or, rarely, as a bone marrow disorder (polycythemia vera).
- Artefact: a PCV tube spun too briefly packs poorly and reads higher.
Lower than reference
A low hematocrit is the core of anemia: blood loss, destruction of red cells (hemolysis), or too little production — for example in kidney disease, chronic inflammation or bone marrow disease. To tell these apart, the vet looks at reticulocytes, young red cells that show whether the marrow is responding.
Some drops are not anemia:
- Dilution by intravenous fluids.
- Sedation or anaesthesia, which relax the spleen so it holds more blood.
- Hemolysis in the tube lowers both HCT and PCV; then hemoglobin × 3 gives a rough estimate of the real hematocrit.
- Too much EDTA (an underfilled tube) shrinks red cells and falsely lowers the calculated HCT.
Look at together with
- Hemoglobin and red cell count — as a rough rule, hematocrit in % is about three times hemoglobin in g/dL.
- Reticulocytes — regenerative or not.
- MCV and MCHC — the size of red cells and how much hemoglobin they carry, which help sort the cause of anemia.
- Creatinine — a non-regenerative anemia in an older animal raises the question of kidney disease.
Units and conversion
Hematocrit is printed either in % or as a fraction in L/L (the SI unit; л/л on Russian-language forms). % ÷ 100 = L/L: 45% is 0.45 L/L. The point to watch is a decimal one: 0.45 and 45 are the same result written two ways, not a hundredfold change. In the app each row keeps the unit printed on the form, and the chart converts everything to one unit. HCT and PCV are recorded as the same indicator.
Reference range
The reference range is on your lab’s form. It differs between species, breeds and analyzers. Dehydration can hide anemia: it can bring the hematocrit of an anemic animal back into the range, or push a healthy animal above the upper limit. That is why a vet reads hematocrit together with hydration and the rest of the blood count, and why a series of tests says more than one result.
Cats and dogs
In cats anemia is usually judged by PCV — this is how the Cornell Feline Health Center describes it. A cat whose anemia developed slowly can look almost normal at home; lethargy is often the first sign. Common feline causes include fleas (especially in kittens), Mycoplasma haemofelis, FeLV and chronic kidney disease — 30–65% of cats with advancing kidney disease develop some degree of anemia.
In dogs breed shifts the picture most: dachshunds, greyhounds and whippets sit higher than other dogs with healthy blood, so a value that looks ordinary against a general canine range can be a drop for a greyhound compared with its own earlier results. Bleeding, immune-mediated hemolytic anemia and infections such as Babesia and Ehrlichia are common causes of a low hematocrit in dogs.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.