Ethylenediaminetetraacetic Acid-dependent Platelet Aggregation, Satellitism, and Phagocytosis in a Case in Which Aggregation was Resolved using Kanamycin Blood Collection Tubes

Abstract

BACKGROUND: This study aimed to investigate ethylenediaminetetraacetic acid (EDTA)-dependent pseudothrombocytopenia (EDTA-PTCP) a rare but significant phenomenon in clinical laboratories that cause diagnostic errors and unnecessary treatments. CASE PRESENTATION: Here, we present an 83-year-old male patient with dyspnea and blood sputum and illustrate how EDTA, commonly used in complete blood count testing, causes falsely low platelet counts due to platelet aggregation and phagocytosis. Initially, the patient’s blood tested by the impedance method with a Sysmex XN-3000 analyzer demonstrated abnormally low platelet counts. However, further tests using different assays (fluorescent platelet count) and anticoagulants indicated the presence of EDTA-PTCP. Blood smear revealed platelet aggregation, satellitism, and phagocytosis that predominantly involve neutrophils. Remeasurements demonstrated significant improvement in platelet count and histogram waveform after incorporating K2-EDTA-added blood to K2-EDTA + kanamycin (KM)-containing vacutainer. These results indicate that remeasuring platelet counts after dissociation of platelet aggregation in EDTA-added blood with an additive such as KM is an effective method of handling EDTA-PTCP when platelet aggregation is observed. In addition, in vitro mixing studies were conducted with healthy control using platelet-poor plasma (PPP), prepared from EDTA and EDTA + KM blood collection tubes. It demonstrated that adding PPP from EDTA + KM tubes to whole blood did not decrease platelet count over time, unlike PPP from EDTA tubes. This revealed that KM, an aminoglycoside antibacterial agent, inhibited platelet aggregating factors in the patient’s plasma. The patient’s positive results for anti-ds-DNAIgG antibodies indicated active systemic lupus erythematosus, emphasizing a potential immunological mechanism of EDTA-PTCP in autoimmune diseases. CONCLUSION: The study reveals that EDTA causes platelet satellitism and phagocytosis by leukocytes, although the exact mechanism of EDTA-induced platelet phagocytosis remains unclear. In conclusion, this case demonstrates that using blood collection tubes other than those containing EDTA salt is a viable option in various laboratories, emphasizing the need for awareness and appropriate management of EDTA-PTCP in clinical practice.