An Unusual Guest in a Peripheral Blood Smear: Circulating Endothelial Cells as an Artifact or an Incidental Finding?

One of the most significant laboratory hematology tests is the peripheral blood smear examination. The clinician may request a peripheral film to confirm a diagnosis or eliminate a differential diagnosis based on the patient's clinical data and other ancillary research findings.[1,2] The peripheral smear of a 62-year-old healthy male was examined for a regular health checkup. A complete blood count showed hemoglobin of 11.2 g/dL, a total leukocyte count of 5.5 × 103/uL with a normal differential leukocyte count, and a platelet count of 170 × 106/uL. The peripheral smear showed normocytic normochromic anemia, and a cluster of medium-to-large-size cells with round-to-oval nuclei, a smooth nuclear membrane, and a moderate amount of weakly basophilic cytoplasm at the tail. The cell cytoplasm is pale blue and ragged at the tapered ends [Figure 1].Figure 1: Peripheral blood smear displaying endothelial cells in groups and clusters showing medium-to-large-size cells having smooth nuclear membrane and moderate amount of basophilic cytoplasm (Leishman stain, ×400)Endothelial cells can be found in the peripheral circulation as foreign cells. Endothelial cells, the inner lining of blood vessels, are rarely detached during venepuncture due to the sharp needles used.[2] Blood films made from the initial needle drop are more likely to have endothelial cells. This is especially true of barbed or poor-quality needles. Endothelial cells increase in various situations that cause vascular injury or rapid blood vessel creation, from benign and reactive events to malignant illnesses.[3] Coronary angioplasty, acute myocardial infarction, peripheral atherosclerosis, systemic lupus erythematosus, rickettsia infection, sickle cell anemia, and allogeneic stem cell transplants increase endothelial cell numbers. This rare appearance and clustering of extraneous cells may be misinterpreted as circulating cancer cells, especially in cases with a worrisome history and clinical symptoms.[3,4] The clinical information of the patient and their morphological characteristics are helpful in recognizing them. Erythropoietin also upregulates vascular endothelial growth factor and its receptor, a vital growth factor and strong angiogenic factor, to encourage new blood vessel creation.[4,5] In conclusion, these findings may be incidental or indicate a new disorder linked to increased endothelial cell numbers. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.