Pseudothrombocytopenia

Pseudothrombocytopenia (PTCP) 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.[1] The phenomenon has first been reported in 1969.[2][3]

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. Pseudothrombocytopenia has been reported in association with the use of EDTA as an anticoagulant, with platelet cold agglutinins, and with multiple myeloma. Other risk factors associated with pseudothrombocytopenia are autoimmune diseases, infections, pregnancy and the treatment with some medications such as low-molecular-weight heparin, valproic acid, insulin, antibiotics and chemotherapy medications like sunitinib.[3]

The prevalence of pseudothrombocytopenia in K2-EDTA reported in different studies ranges from 0.03 to 0.27 percent in outpatients,[3] which accounts for 15 to 30 percent of all cases of isolated thrombocytopenia. Tests can mistake small clumps of platelets for leukocytes, thus showing a pseudo­leukocytosis in blood counts.[4]

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 sodium citrate (blue top tube) to confirm the finding of pseudothrombocytopenia may be requested if there are doubts or concerns. Other alternative anticoagulants are sodium fluoride, CPT (trisodium citrate, pyridoxal 5′-phosphate and tris), CTAD (citrate, theophylline, adenosine, and dipyridamole), magnesium sulfate and acid-citrate-dextrose.[3]

References
  1. "Clinical & Applied". July 1998 vol. 4 no. 3 167-169. SAGE Journals. Retrieved 12 May 2013.
  2. Gowland E; Kay HE; Spillman JC; Williamson JR (1 July 1969). "Agglutination of platelets by a serum factor in the presence of EDTA". Journal of Clinical Pathology. 22 (4): 460–464. doi:10.1136/JCP.22.4.460. ISSN 0021-9746. PMC 474212. PMID 4978997. Wikidata Q36546397.
  3. Benjamin Lardinois; Julien Favresse; Bernard Chatelain; Giuseppe Lippi; François Mullier (4 February 2021). "Pseudothrombocytopenia—A Review on Causes, Occurrence and Clinical Implications". Journal of Clinical Medicine. 10 (4): 594. doi:10.3390/JCM10040594. ISSN 2077-0383. PMC 7915523. PMID 33557431. Wikidata Q116885099.
  4. Nicola Bizzaro (1 October 1995). "EDTA-dependent pseudothrombocytopenia: a clinical and epidemiological study of 112 cases, with 10-year follow-up". American Journal of Hematology. 50 (2): 104. doi:10.1002/AJH.2830500206. ISSN 0361-8609. PMID 7572988. Wikidata Q33488487.

Further reading
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