Pseudothrombocytopenia in a Clinically Well Cat
A 6-year-old spayed female domestic shorthair (4.0 kg) is presented for a routine wellness exam. The in-house analyzer reports platelets 38,000/microliter, WBC 12,000/microliter, HCT 36%, and total protein 7.4 g/dL. The cat is bright, eating normally, with no petechiae, epistaxis, or melena. A blood smear made from the same EDTA tube shows several large platelet clumps and moderate rouleaux; no platelet-associated antibodies are tested. The sample was collected 3 hours earlier from the jugular vein and had been refrigerated.
1. How do you interpret the platelet count, and what is the next step?
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The automated count is likely falsely low because the analyzer does not count platelets that are trapped in large clumps. The cat has no bleeding signs, and the smear directly shows platelet clumps, so pseudothrombocytopenia is the leading explanation. Do not start immunosuppressive therapy or order a platelet transfusion based on this result. Repeat the platelet count using a fresh sample, make a blood smear immediately, and count platelets manually. If clumping persists, collect a citrate tube and correct the count for dilution. Treat true thrombocytopenia if the count remains severely low and the cat has bleeding or other abnormalities.
2. What sample-handling errors are present, and how would you correct them?
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The EDTA sample was refrigerated and was 3 hours old before analysis. Cold storage can promote platelet clumping and degranulation, and delayed analysis can alter cell counts and morphology. For a CBC, keep the sample at room temperature, analyze it promptly, and make the smear from a fresh drop soon after collection. If EDTA-induced clumping is suspected, submit a citrate sample and remember that citrate dilutes the sample; the reported platelet count must be corrected for that dilution. Do not use a clumped, refrigerated sample as the sole basis for a diagnosis.
3. The owner asks if the cat needs a platelet transfusion. Explain your reasoning.
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No. A platelet transfusion is not indicated for an artifact in a cat with no bleeding. The cat is clinically well, and the low analyzer count is explained by platelet clumping. Transfusion carries risks and is reserved for true severe thrombocytopenia with active bleeding or a high risk of bleeding. The next step is a repeat, properly handled platelet count and manual smear review. If the repeat count is truly below about 20,000-30,000/microliter with bleeding, then transfusion and further diagnostics would be considered.