MPV (mean platelet volume) in cats and dogs
MPV, the mean platelet volume, is the average size of platelets — the small cell fragments that start blood clotting. Analyzers print it next to the platelet count, often together with PDW and P-LCR, other indices of platelet size. Large platelets can hint that the marrow is making new ones, but in cats and dogs a common reason for a high MPV is platelets clumped together in the tube.
What it shows
Platelets are made in the bone marrow: large cells called megakaryocytes break up into fragments under the influence of the hormone thrombopoietin. An automated analyzer measures the volume of each platelet it counts and reports the average in femtolitres (fL).
Large platelets are often young, so when the platelet count is low, a higher MPV is a “soft” clue that the marrow is responding. eClinPath warns that not every large platelet is young — some are large because production is defective — so platelet size on its own is not a reliable measure of a marrow response.
Higher than reference — what it may be a sign of
- Platelet clumps — the most common laboratory reason. The analyzer “sees” a clump as one very large platelet, so the MPV goes falsely up while the platelet count goes falsely down. Clumping is especially frequent in cats; laboratories check the count on a blood smear.
- An old sample: platelets swell while blood waits in the EDTA tube, which raises the MPV.
- Active platelet production: after platelets are lost or used up, the marrow may release younger, larger ones. This is read only together with the count and the smear.
- Inherited macrothrombocytopenia in Cavalier King Charles spaniels: an inherited defect gives fewer but larger platelets. In an eClinPath case the dog had an MPV of 22.6 fL and a count of 71 thousand/µL without any bleeding — the large size makes up for the lower number.
Lower than reference
A low MPV means that platelets are small on average. The veterinary sources used for this article do not describe a specific disease meaning for a low MPV in cats and dogs, and a vet rarely draws conclusions from it alone. It is read together with the platelet count, the plateletcrit and a look at the blood smear.
Look at together with
- Platelet count — MPV only makes sense next to the number of platelets: large platelets with a low count are read differently from large platelets with a normal count.
- Plateletcrit (PCT) — the total platelet mass; it shows whether larger platelets make up for a lower number.
- Blood smear review — confirms or rules out clumps, the main source of a falsely high MPV and a falsely low count.
Units and conversion
MPV is reported in femtolitres: fL, or фл on Russian forms. It is the same unit everywhere, so no conversion is needed.
Some analyzers add other size indices; each answers its own question:
- PDW (PDW-CV), platelet distribution width in % — how much platelet sizes vary relative to the average.
- PDW-SD — the same spread expressed in fL, as an absolute width of the size distribution.
- P-LCR, platelet large cell ratio in % — the share of platelets above a size threshold set by the analyzer.
These indices cannot be converted into one another, and the same index from different analyzers is not always comparable. In the app each row keeps the unit printed on the form.
Reference range
The reference range is on your lab’s form. Platelet indices depend strongly on the analyzer and on how long the sample waited before testing, so ranges from one lab do not transfer to another. A single high MPV with a normal count and no clumps on the smear rarely means much; a series of tests on the same analyzer says more than one result.
Cats and dogs
In cats platelets clump easily during blood collection, so analyzers often give a falsely low platelet count with a falsely high MPV. This is why a vet looks at the smear before reading anything into a cat’s MPV. Platelet size also varies within one sample more than the averages suggest, in cats and dogs alike, even in healthy animals.
In dogs breed matters most. Cavalier King Charles spaniels often carry an inherited macrothrombocytopenia: a lower platelet count with large platelets and normal total platelet mass, usually without bleeding; a genetic test is available. Greyhounds can have lower platelet counts and lower plateletcrits than other breeds.
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.