Red blood cell count (RBC) in cats and dogs
The red blood cell count (RBC) is the number of red cells in a volume of blood. Together with hemoglobin and hematocrit it shows whether an animal has enough red blood: a low count points to anemia, a high one most often to dehydration.
What it shows
Red blood cells carry oxygen to the tissues. The analyzer counts them as they pass one by one through a narrow opening or a laser beam, and at the same time measures their size — that is where the MCV comes from.
The red cell count, hemoglobin and hematocrit are, in the words of the Merck Veterinary Manual, three ways to measure the same thing, and reading them as separate findings is a mistake. Vets lean mostly on hematocrit or PCV; the red cell count matters as a building block: the analyzer’s hematocrit is calculated from RBC and MCV, and MCH from hemoglobin and RBC. When the three numbers move together, the picture is clear; when RBC disagrees with the other two, the sample is the first suspect.
Higher than reference — what it may be a sign of
- Dehydration — a frequent reason. The blood loses water, so the same red cells sit in less plasma: after vomiting, diarrhoea or not drinking enough. This is a relative increase.
- Breed: dachshunds, greyhounds and whippets can have higher red cell counts, hematocrit and hemoglobin with healthy blood.
- 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: water evaporating from a poorly closed tube concentrates the sample.
Lower than reference
A low count is a sign of anemia. Vets sort it by mechanism:
- Blood loss: injury, a bleeding tumour, stomach ulcers, parasites.
- Destruction of red cells (hemolysis): immune-mediated, blood parasites, toxins.
- Too little production: kidney disease, chronic inflammation, bone marrow disease, FeLV in cats.
The marrow needs time to answer: according to the Merck Veterinary Manual, a regenerative response takes 3–5 days, so right after acute bleeding the anemia can look non-regenerative. A drop can also be relative — after intravenous fluids, or under sedation and anaesthesia, when the spleen relaxes and holds more blood. If red cells burst in the tube (hemolysis during collection or storage), the count is falsely low; then measured hemoglobin reflects the oxygen-carrying capacity better.
Look at together with
- Hemoglobin and hematocrit — the other two members of the trio.
- Reticulocytes — young red cells; they show whether the marrow is responding.
- MCV, MCH, MCHC and RDW — size of red cells, their hemoglobin and how much they vary.
- Creatinine — a non-regenerative anemia in an older animal raises the question of kidney disease.
Units and conversion
The red cell count is reported as 10¹²/L (the SI unit; ×10¹²/л on Russian-language forms) or as millions per microlitre — 10⁶/µL, M/µL, млн/мкл. These are the same number with a factor of 1: 7 × 10¹²/L is 7 million per microlitre. In the app each row keeps the unit printed on the form, and the chart converts everything to one unit so results from different labs line up.
Reference range
The reference range is on your lab’s form. It differs between species, breeds and analyzers. Dehydration can hide anemia: in a dehydrated anemic animal the red cell count and hematocrit can still sit inside the range, and the drop shows only once fluids are restored. That is why a vet reads the count together with hydration, hemoglobin and hematocrit, and why a series of tests says more than one result.
Cats and dogs
In cats the first sign of anemia is often lethargy, and a cat whose anemia developed slowly can look almost normal at home. The Cornell Feline Health Center names fleas and ticks (especially in kittens), Mycoplasma haemofelis, toxins such as paracetamol and onion, and chronic kidney disease: 30–65% of cats with advancing kidney disease develop some degree of anemia. Cats are also more prone than other species to Heinz bodies — oxidative damage to red cells.
In dogs breed matters most for a high count: dachshunds, greyhounds and whippets often sit higher than other dogs with healthy blood. Among causes of a low count are bleeding (including a ruptured splenic tumour), immune-mediated hemolytic anemia and infections such as Babesia and Ehrlichia.
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.