Hematocrit (HCT / PCV)
Blood count (CBC) ·Also called: HCT, PCV, packed cell volume, haematocrit
What it is
Haematocrit expresses how much of a blood sample is cells rather than plasma. The same value measured by spinning a capillary tube by hand is called packed cell volume, or PCV, and the two names are used interchangeably on reports.
Why your vet measures it
PCV can be run in minutes on a drop of blood, so it is often the first number a vet has in an emergency. A falling haematocrit in a collapsed animal points to bleeding; a very high one in a flat, vomiting pet points to dehydration. It guides urgent decisions before the full panel comes back.
What a high result can mean
- Dehydration — by far the most common reason, and it resolves with fluids
- Stress or excitement, particularly in cats, through splenic contraction
- Chronic low oxygen from heart or lung disease
- Polycythaemia vera, a rare bone marrow disorder
What a low result can mean
- Blood loss, acute or slow and hidden
- Immune-mediated destruction of red cells, one of the more common canine emergencies
- Chronic kidney disease, marrow suppression, or chronic inflammation
- Over-hydration from intravenous fluids, which dilutes the sample
Dogs and cats differ
Healthy cats sit lower than healthy dogs — a cat at 32 per cent may be entirely normal where the same figure in a Labrador would prompt questions. Sighthounds run high, often into the high 50s. Puppies and kittens are normally lower than adults until a few months old.
Questions worth asking your vet
- Is my pet dehydrated, and would this value change after fluids?
- If it is low, is the bone marrow responding — what do the reticulocytes show?
- How quickly has this changed compared with the last test?
Related terms
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