Platelet clumping in a blood sample in cats and dogs
Platelet clumps are platelets that have stuck together in the tube after the blood was taken. The analyser then misses them or counts a clump as one large platelet, so the platelet count comes out lower than it really is. The note is mainly about the quality of the sample, and it is especially common in cats: a low count with clumps does not by itself mean a true shortage of platelets.
What it shows
Platelets react quickly to anything that activates them — a slow or difficult blood draw, delayed mixing with the anticoagulant, waiting before the count. Once activated in the tube, they stick together. Clumps lower the platelet count whatever counting method is used, so any number reported with clumps is read as a minimum: the real count is at least that high. Small clumps are often counted as single large platelets, which also pushes up the mean platelet volume. With severe clumping the count may be invalid altogether, and the lab reports only an estimate from the smear.
Because of this, every blood smear is checked for clumps, at the feathered edge and in the body of the smear, before a low platelet count is accepted.
Higher than reference — what it may be a sign of
- A collection or handling problem — the most usual explanation. Clumping increases the longer blood stands before the count.
- A sick animal. Clumping can also occur with a clean blood draw in sick animals.
- EDTA-induced clumping — rare; reported in dogs and horses. Here clumping happens only in EDTA, so the count is repeated on blood in citrate, where this does not happen.
On some analysers, numerous clumps are also counted as white cells, so the white cell count can be falsely high in the same sample. Whether platelets are truly low is then judged from the smear estimate or a new, carefully taken sample.
Lower than reference
“No clumps” makes the analyser count more trustworthy, but not perfect. Some analysers miss very large platelets and underestimate the count even without clumping. When clumps are present, the smear estimate is not exact either, because clumps are spread unevenly across the slide.
Look at together with
- Platelets — the count that clumps make falsely low.
- MPV — mean platelet volume, which clumps can falsely raise.
- Total white cell count — some analysers count clumps as white cells.
- Manual differential — the smear scan where clumps are seen.
- Plateletcrit — the share of blood volume taken up by platelets.
Units and conversion
There are no units: the lab notes whether clumps are present, sometimes with an amount in words (for example few or many). Next to it there may be a smear estimate of the platelet count in categories such as increased, adequate, low or very low. In the app the result is stored as text, as written on the form.
Reference range
The reference range is on your lab’s form. There is no number to compare against. In a well-taken sample clumps are not expected; when they are noted, the platelet count on the same form is best read as a lower limit rather than as the true value.
Cats and dogs
Cats are known for platelet clumping: their platelets activate at the slightest provocation during collection and handling, which makes accurate counts difficult. Feline platelets are also large and hard for many analysers to separate from red cells, even without clumps. A stained smear is therefore checked before a low count is reported in a cat.
In dogs clumping mostly follows a difficult blood draw. Rarely, platelets clump only in EDTA, and the count is repeated in citrate. Cavalier King Charles Spaniels, Norfolk Terriers and some other breeds can have an inherited low count of large platelets without any illness — a different situation that the smear also helps to recognise.
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
- eClinPath (Cornell University College of Veterinary Medicine). Platelet count.
- eClinPath (Cornell University College of Veterinary Medicine). Platelet number.
- eClinPath (Cornell University College of Veterinary Medicine). MPV.
- eClinPath (Cornell University College of Veterinary Medicine). WBC counts.
- Today’s Veterinary Practice. Blood Smear Review: A Step-by-Step Guide to Normal Findings for Cats and Dogs.
- Harvey JW. The feline blood film: 2. Leukocyte and platelet morphology. Journal of Feline Medicine and Surgery, 2017.
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.