Pseudothrombocytopenia

Abstract

Introduction: Pseudo thrombocytopenia (PTP) is a phenomenon of falsely low platelet counts obtained on Hematology Analyzers (HA) due to in vitro platelet clumping in the presence of anticoagulants. Methods: Papers on the subject of pseudothrombocytopenias effects were searched for in biomedical journals indexed in MEDLINE from 1969 to 2016. All other thrombocytopenia types were not analyzed. Topic: Pseudothrombocytopenia occurs using the EDTA and other anticoagulants, in the process of determining the platelet count on the HA. Agglutination of platelets occurs at temperatures lower than 34° C and sample enhances if exposed to longer period of time. Agglutination of platelets is most expressed 4 hours after blood sampling. Agglutination occurs by binding of IgM, IgG and IgA immunoglobulin to antigen or crypto- antigen of platelets. Hematologic cell Analyzers, (HA) do not count platelets from large agglutinations, therefore, the number of platelets that provides HA represents the sum of the number of free non-agglutinating platelets and small agglutinations consisting of 3-5 platelets. Pseudothrombocytopenia shall be suspected in the case of the absence of clinical signs of hemorrhagic diathesis. Undiagnosed pseudothrombocytopenia may lead to unnecessary aggressive diagnostic procedures such as biopsy or puncture of the bone marrow, inadequate treatment and even transfusion of platelets. The fallowing types of pseudothrombocytopenias are described herein: a) pseudothrombocytopenia occurred due to platelet agglutination, b) platelet satellitism and c) aggregation of platelets and leukocytes. Conclusion: In order to obtain the actual count of platelets, peripheral blood smear shall be done for all samples with low values of thrombocytes (<100x109 / L), and for samples of the results having flags on HA. In the case of finding agglutinated platelets, the following measures should be taken in order to obtain correct interpretation of laboratory results: to warm blood sample at 37° C and re-test, to test the blood sample on the another anticoagulant (citrate, heparin), to make blood smear, and to determine the platelets using ammonium oxalate by counting platelets from capillary blood in microscopic counting chamber. In case of all phenomena of agglutinations with all the previously mentioned anticoagulants is only possible to use magnesium sulphate and to make smears on the site of capillary blood sampling. Using this method is as well possible to detect agglutination of platelets without using anticoagulants, which indicates the presence of cold agglutinins. .