Recognition of Transfusion With Microcytic Packed Red Blood Cells on <scp>ADVIA</scp> 2120i <scp>RBC</scp> V/ <scp>HC</scp> Cytograms: A Case Report

A 3-year-old, intact female Havanese dog was presented for treatment of a relapse of suspected immune-mediated anemia and thrombocytopenia. Over the course of treatment, the patient's anemia appeared to acutely transition from macrocytic and hypochromic to microcytic and hypochromic between days five and six of hospitalization. Assessment of red blood cell volume/hemoglobin content (RBC V/HC) cytograms produced on the ADVIA 2120i (Siemens Healthcare Diagnostics, Munich, Germany) revealed a new population of microcytic and hypochromic erythrocytes on day six of hospitalization. This finding prompted the consideration that the microcytic and hypochromic erythrocyte population was introduced to the patient via a packed red blood cell (pRBC) transfusion, which was confirmed after running a sample of pRBCs from the same donor through the ADVIA 2120i. Other causes of microcytosis, such as iron deficiency anemia, portosystemic shunt, and hyponatremia, were additionally investigated and considered less likely. The cause of the microcytosis in the donor was ultimately undetermined. To the authors' knowledge, this is the first case where inadvertent transfusion with microcytic pRBCs was discovered with the aid of RBC V/HC cytograms. This case highlights the importance of considering pRBCs as a source of changes in erythrocyte indices as well as the utility of RBC V/HC cytograms in patients with multiple populations of erythrocytes, such as those receiving transfusions. Additionally, this case prompts reconsideration of the need for standardization of guidelines for blood donation frequency and monitoring of iron status in frequent blood donors.