Pseudothrombocytopenia

Pseudothrombocytopenia or spurious thrombocytopenia is an in-vitro sampling problem which may mislead the diagnosis towards the more critical condition of thrombocytopenia. The phenomenon occurs when the anticoagulant used while testing the blood sample causes clumping of platelets which mimics a low platelet count.

Causes

It is a relatively uncommon phenomenon caused by in vitro agglutination of platelets. As a result of platelet clumping, platelet counts reported by automated counters may be much lower than the actual count in the blood because these devices cannot differentiate platelet clumps from individual cells. The incidence of pseudothrombocytopenia reported in different studies ranges from 0.09 to 0.21 percent, which accounts for 15 to 30 percent of all cases of isolated thrombocytopenia.Pseudothrombocytopenia has been reported in association with the use of ethylenediaminetetraacetic acid (EDTA) as an anticoagulant, with platelet cold agglutinins,and with multiple myeloma.

Failsafes and avoiding false-positives

A pseudothrombocytopenia false-positive result may occur when automated platelet counting devices are used. As a means of double checking the results, the patient's blood sample is often examined under a microscope. If the clumping is visible and the number of platelets appears normal, pseudothrombocytopenia may be concluded. A second sample run with a different anticoagulant such as citrate (blue top tube) to confirm the finding of pseudothrombocytopenia may be requested if there are doubts or concerns.

References

• Pseudothrombocytopenia or platelet clumping as a possible cause of low platelet count in patients with viral infection: a case series from single institution focusing on hepatitis A virus infection. W.-H. Choe et al. International Journal of Laboratory Hematology, Volume 35, Issue 1, pages 70–76, February 2013