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Low platelets in cats: why the count is often falsely low

A low platelet count is one of the most common surprises on a cat’s blood test, and often not a real one. Cat platelets clump together in the tube very easily, and the analyser cannot count clumps. Here is how vets check whether the count is true and what they look for if it is.

Written by the AI DiagAnimals editorial teamReviewed by the AI DiagAnimals TeamUpdated Our editorial policy

The essentials

Cat platelets are very reactive and clump in the tube, which falsely lowers the automated count: in a study of 100 healthy cats, clumps were seen in 56% of standard samples. A low count is therefore checked on a blood smear first. A true low count is less common in cats than in dogs; spontaneous bleeding is unlikely unless platelets fall below about 30,000/µL.

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Why cat platelet counts are often falsely low

Cats have notoriously reactive platelets, which clump readily when blood is taken, so obtaining an accurate platelet count can be difficult in a cat [1]. Clumping is more likely after a difficult blood draw or from a small vein [1, 2].

In 100 healthy cats, platelet clumps were seen in 56% of samples kept in standard EDTA tubes [3]. Other anticoagulants that inhibit platelets reduce clumping and give higher counts [4]. Clumps can also make the average platelet size (MPV) look falsely high [1].

How to read the platelet line

Here is an example line from a cat’s blood count.

An annotated line from a lab report · Illustrative example
AbbreviationResultUnitLaboratory intervalFlag
PLT Platelets9210³/µL300–800L
  1. Abbreviation PLT or platelets. The analyser may add a comment such as “clumps” or “aggregates”.
  2. Result 92 × 10³/µL in this illustrative line, i.e. 92,000 platelets per microlitre.
  3. Unit 10³/µL, 10⁹/L or G/L: the same number in all three.
  4. Laboratory interval The example uses the cat interval of the Merck Veterinary Manual [5].
  5. Flag L: below the interval. The next step is a look at the blood smear for clumps [1].

How the smear confirms the count

The laboratory or your vet looks at a stained blood smear. Clumps usually gather at the thin edge of the smear. Each platelet seen per high-power oil field corresponds to roughly 15,000/µL, so 10 to 15 or more per field means an adequate count even when the analyser says otherwise [1].

Some healthy cats also have very large platelets that analysers can miss, another source of falsely low counts [1].

When the low count is real

  • Consumption, when platelets are used up in clotting, for example in severe illness with disseminated clotting (DIC) [2].
  • Reduced production in the bone marrow, from infections, cancer or drugs [2].
  • Destruction by the immune system. Primary immune thrombocytopenia is rare in cats; anti-thyroid drugs such as methimazole are among the drugs that can trigger it [2].
  • Blood loss and dilution after large fluid volumes [2].

Platelets alone rarely cause spontaneous bleeding unless they fall below about 30,000/µL; after trauma or surgery, bleeding can occur below about 50,000/µL [1].

Results often read with platelets

Red and white cells

If they are also low, the bone marrow may be involved.

Read the article

Cat blood work overview

The other cat-specific pitfalls: stress and haemolysis.

Read the article

Low platelets in dogs

The same question in dogs, with its own causes.

Read the article

En français : thrombopénie du chat.

Questions to ask your veterinarian

  1. Did the analyser or the smear show platelet clumps?
  2. What does the smear estimate say about the platelet number?
  3. Should we repeat the count on a fresh sample, ideally from a larger vein?
  4. If the count is truly low, which causes should we look for?
  5. Could one of my cat’s medicines be involved?
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Frequently asked questions

Why does my cat have a low platelet count?

Most often because platelets clumped in the tube, which the analyser cannot count. A blood smear tells whether the count is truly low [1, 3].

When should I worry about low platelets in my cat?

When the smear confirms a low count, or if your cat shows bruising, red dots on the gums or bleeding. Spontaneous bleeding is unlikely above about 30,000/µL [1].

Can a cat recover from low platelets?

Yes, when the cause is found and treated, for example by stopping a drug or treating an infection. Many low counts in cats were never real in the first place [2, 3].

What is a normal platelet count for a cat?

About 300–800 × 10³/µL in the Merck Veterinary Manual table; your laboratory’s interval applies [5].

Does a difficult blood draw affect the result?

Yes. Clumping is more common after a difficult draw or from a small vein [1, 2].

Sources

  1. eClinPath, Cornell University College of Veterinary Medicine. Platelet number. eclinpath.com/hemostasis/tests/platelet-number
  2. eClinPath, Cornell University College of Veterinary Medicine. Platelet numbers: disorders. eclinpath.com/hemostasis/disorders/platelet-numbers
  3. Engelmann AM et al. Amikacin prevents platelet aggregation in feline venous blood samples. Vet Clin Pathol. 2022;51(1):51-56. doi.org/10.1111/vcp.13074
  4. Norman EJ et al. Evaluation of a citrate-based anticoagulant with platelet inhibitory activity for feline blood cell counts. Vet Clin Pathol. 2001;30(3):124-132. doi.org/10.1111/j.1939-165x.2001.tb00420.x
  5. Merck Veterinary Manual. Hematology (complete blood count) reference ranges. merckvetmanual.com/reference-values-and-conversion-tables/reference-guides/hematology-reference-ranges

Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.

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