Anticoagulant-dependent pseudothrombocytopenia (PTDA) is characterized by an in vitro reduction in platelet count due to platelet aggregation in blood samples collected with anticoagulants, such as EDTA, where aggregates are erroneously counted as giant platelets or small lymphocytes. To confirm PTDA, a repeat blood draw using 3.2% buffered sodium citrate is necessary, as it rarely causes thrombocytopenia. PTDA can lead to incorrect diagnoses and severe clinical consequences, especially during acute phases and when considering the presence of diseases and medications. This study aims to report a case of EDTA-induced PTDA in a patient with breast cancer undergoing chemotherapy, emphasizing the importance of accurate identification and the need to use different anticoagulants to confirm true thrombocytopenia.

We present the case of a 69-year-old woman with breast cancer undergoing chemotherapy who exhibited EDTA-induced PTDA at the Antonio Pedro University Hospital, Federal Fluminense University. Seven complete blood counts were performed, with erythrocytic and leukocytic parameters within normal ranges, but platelet counts varied between 19 ×103/μL and 40 ×103/μL, indicating severe thrombocytopenia. Blood smear analysis did not confirm thrombocytopenia, and the patient exhibited no symptoms consistent with the condition. Blood collected with EDTA showed platelet aggregation, whereas blood collected with 3.2% buffered sodium citrate yielded a normal platelet count of 230 ×103/μL.

This case illustrates a patient with breast cancer undergoing chemotherapy who developed pseudothrombocytopenia. Thrombocytopenia, defined as a platelet count below 150 ×10/L, can result from viral infections, malignancies, chemotherapy, or autoimmune diseases. Chemotherapy-related thrombocytopenia is common, affecting approximately 13% of patients with solid tumors. In contrast, PTDA is a rare laboratory artifact. Although the precise mechanism of EDTA-dependent pseudothrombocytopenia is not fully understood, healthcare professionals must recognize this condition as a potential risk when interpreting abnormal platelet counts in clinical contexts.

The delay in identifying EDTA-induced pseudothrombocytopenia adversely affected the patient's chemotherapy treatment, highlighting the need for increased awareness of this phenomenon to prevent incorrect diagnoses and their potential clinical implications.