MCV (mean cell volume) in cats and dogs
MCV (mean cell volume, also mean corpuscular volume) is the average size of a red blood cell. On its own it rarely decides anything, but together with MCHC it helps a vet sort out why an animal is anemic: large cells often go with regeneration, small ones with iron deficiency.
What it shows
Modern analyzers measure the volume of each red cell directly — by laser light scatter or by the change in electrical resistance as a cell passes a small opening — and average it over all cells counted. Older methods calculated MCV from the packed cell volume and the red cell count.
Vets use MCV and MCHC as a pair to describe anemia: normocytic or macrocytic or microcytic (normal-sized, large or small cells), normochromic or hypochromic. eClinPath notes that these patterns can guide the vet to the mechanism and the likely cause of anemia. MCV differs a lot between species, so cat and dog values are not interchangeable.
Higher than reference — what it may be a sign of
Large red cells (macrocytosis):
- Regenerative anemia: young red cells are larger, so after bleeding or hemolysis MCV can rise; on laser analyzers the effect is less visible.
- Breed: miniature and toy poodles can have MCV up to 90 fL without anemia.
- Disease of the marrow: in cats a disorder of blood cell formation (myelodysplasia) is usually caused by FeLV; folate or vitamin B12 deficiency and some medicines also enlarge cells.
- Inherited red cell membrane disorders, such as hereditary stomatocytosis in Alaskan malamutes and miniature schnauzers.
- Sample artefacts: clumped (agglutinated) red cells counted as one big cell, often giving values above 90 fL on impedance analyzers; cells that swell while a sample waits, especially if not kept cool; high blood sodium on some analyzers.
Lower than reference
Small red cells (microcytosis):
- Iron deficiency — the most common cause, usually from chronic blood loss. eClinPath explains that cells keep dividing while waiting for enough hemoglobin, so each generation comes out smaller.
- Liver disease, especially a portosystemic shunt (a vessel that lets blood bypass the liver); microcytosis often goes away after the shunt is closed.
- Breed: Akitas, and possibly Shiba Inu, Shar-Pei and Siberian huskies, can have small red cells without anemia.
- Age: puppies and kittens younger than roughly 8–16 weeks can have smaller red cells.
- Artefact: too much EDTA (an underfilled tube) dehydrates cells and lowers MCV.
Look at together with
- MCHC — hemoglobin concentration in the cells; the second half of the classification.
- RDW — how much cells vary in size; a small group of unusual cells can raise it before MCV moves.
- Reticulocytes — whether large cells reflect a marrow response.
- Hematocrit and hemoglobin — whether there is anemia at all.
- Blood smear — confirms the size change and shows clumping.
Units and conversion
MCV is reported in femtolitres (fL; фл on Russian-language forms). One femtolitre is 10⁻¹⁵ litre, the same as one cubic micrometre, so forms that print µm³ (мкм³) show the same number: the factor is 1. In the app each row keeps the unit printed on the form, and the chart converts everything to one unit.
Reference range
The reference range is on your lab’s form. It depends heavily on species and on the analyzer: according to the Merck Veterinary Manual, average red cell volume ranges from about 15 fL in goats to about 90 fL in people. A small shift inside the range rarely means much; a trend across several tests, together with reticulocytes and MCHC, says more.
Cats and dogs
In cats young red cells can stay in the blood for up to 3 weeks after recovery from a regenerative anemia, keeping MCV high for a while (post-regenerative macrocytosis). Macrocytosis in an anemic cat without signs of regeneration raises the question of FeLV-related marrow disease. Hyperthyroidism has been linked to higher MCV in some studies. In one study Abyssinian cats had lower MCV than other breeds.
In dogs breed matters: poodles can have large red cells, Akitas and possibly Shiba Inu, Shar-Pei and Siberian huskies small ones, all with healthy blood. Iron deficiency from chronic blood loss and portosystemic shunts are the usual reasons for small cells. In immune-mediated hemolytic anemia the round, dense spherocytes look small on the smear but usually have a normal volume, so microcytosis is unusual.
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.