Diagnosis of EDTA-dependent pseudothrombocytopenia in a horse.

The research paper describes a case of EDTA-dependent pseudothrombocytopenia in a horse, a condition where platelet counts appear lower due to the presence of Ethylenediaminetetraacetic acid (EDTA), an anticoagulant used in blood samples. The findings suggest that this condition should be taken into consideration in horses where thrombocytopenia is diagnosed without signs of a bleeding tendency.

Background and Aim of the Study

• The research primarily focuses on diagnosing causes of thrombocytopenia in horses, a condition characterized by a lower than normal number of platelets — the cells responsible for clotting — in the blood.
• This can be due to various causes, including infectious diseases such as equine infectious anemia, lymphosarcoma, drug administration, bone marrow suppression, myelophthisic disease, or disseminated intravascular coagulation. However, in this study, the authors specifically look into EDTA-dependent pseudothrombocytopenia.
• Pseudothrombocytopenia refers to a condition where the platelet count appears low due to the clumping of platelets, when in reality, they may be within the normal range. The authors aim to further investigate this condition in horses.

Methodology and Findings: EDTA vs Heparin

• The diagnosis in this study was performed by comparing the platelet count in two different blood samples, one with EDTA, and the other with heparin, another common anticoagulant used in blood samples.
• It was found that in the blood containing EDTA, the platelet counts were consistently less than the reference range, indicating a lower platelet count.
• However, with the blood sample containing heparin, the platelet counts were within the reference range, meaning they were normal.
• This suggested EDTA-dependent pseudothrombocytopenia, where the low platelet count was tied to the presence of EDTA, not an actual deficiency of platelets.

Conclusion and Significance

• This study shows that when thrombocytopenia is diagnosed in horses without clinical evidence of a bleeding tendency, EDTA-dependent pseudothrombocytopenia should be considered.
• This condition can be confirmed by screening blood films for platelet clumps and comparing platelet counts of paired blood samples, one containing EDTA and the other containing heparin.
• The study’s findings have important implications for diagnosing thrombocytopenia in horses, as it saves unnecessary treatments for low platelet count when the condition is EDTA-dependent pseudothrombocytopenia.