What Is Pseudothrombocytopenia?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 19 August 2018
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Pseudothrombocytopenia is the appearance of low platelets in a blood test that is caused by an in-vitro problem with the blood collection, rather than a disorder in the patient. Clinically, it may cause concern and confusion because there could be worries about the patient’s health, but there are some steps that can be taken when thrombocytopenia is suspected to distinguish between a true case and a false positive. It is important to evaluate patients carefully to avoid potentially costly and invasive testing like bone marrow biopsy to check on platelet function.

In some cases, when blood is processed with a chemical called Ethylenediaminetetraacetic Acid (EDTA) as an anticoagulant, it causes platelet clumping. Automated platelet counting equipment will report that the count is low, indicative of thrombocytopenia, where the patient’s blood doesn’t have enough platelets. This is a potential concern, because it could put the patient at risk of excessive bleeding and complications like bruising, damage to joints, and related issues.

If the blood is examined under a microscope, the clumping will be visible and the number of platelets will appear normal. This suggests pseudothrombocytopenia, which means the patient’s platelet count is perfectly fine and the problem lies with the anticoagulant used. A second sample run with a different anticoagulant to confirm the finding may be requested if there are doubts or concerns. Repeat samples should show a normal platelet count, indicating that the patient’s blood chemistry is healthy, at least in this respect.


Routine blood testing is common for evaluation of patients with suspected medical disorders, and false positives like pseudothrombocytopenia do occasionally occur. Labs use a variety of failsafes to avoid them and have measures in place to address positive results when they arise so they can be confirmed with a minimum of disruption for the patient. In a situation where lab results indicate thrombocytopenia but the patient doesn’t have symptoms like fatigue and excessive bleeding, the medical provider may consider pseudothrombocytopenia. Technicians can check the blood under the microscope to count the platelets and if necessary a second blood test can be performed.

Patients who do have symptoms suggestive of thrombocytopenia may need a follow-up test with a different anticoagulant to confirm the positive results. If the second test indicates the platelet count is indeed low, additional testing to explore the cause may be recommended. This can help the medical practitioner develop recommendations for treatment to stabilize the patient’s platelets and prevent complications.


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