Codocytosis in the Dog: 345 Cases (2020–2022)

INTRODUCTION: Codocytes, or target cells, are a morphologic variation of erythrocytes characterized by increased membrane surface area relative to volume. In dogs, codocytosis is frequently noted on blood smear evaluation, but its clinical significance remains poorly understood. OBJECTIVES: To characterize the clinical conditions associated with codocytosis in dogs and assess relationships between codocyte severity and hematologic, biochemical, and diagnostic findings. METHODS: A retrospective descriptive study was conducted on 345 dogs from a veterinary teaching hospital from September 2020 through October 2022. Dogs were included if their CBC report described codocytosis graded as ≥ 2+. Data collected included CBC results, serum biochemistry, clinical diagnoses, and current medications. Codocytosis was graded semi-quantitatively (2+ to 4+). Statistical comparisons were made using chi-square tests. RESULTS: Codocytosis ≥ 2+ was identified in 2.5% of 14 010 canine CBCs during the study. The majority (81.4%) had 2+ codocytes. There were no significant differences in anemia, macrocytosis, or regeneration across grades. Dogs with 3+ or 4+ codocytosis had significantly higher alanine transferase (ALT) activity and were more frequently diagnosed with hepatobiliary (p = 0.006) and gastrointestinal (p = 0.009) diseases. Endocrine disease, particularly diabetes mellitus was also frequently observed. Antibiotic use was significantly associated with higher codocyte grades (p < 0.001), though no causation was identified. CONCLUSIONS: Codocytosis in dogs is not primarily associated with anemia or regeneration, but rather appears more frequently in diseases affecting hepatobiliary, gastrointestinal, and endocrine systems. These findings suggest a multifactorial pathogenesis likely involving altered lipid metabolism and membrane remodeling. Recognition of codocytosis may provide insight into systemic disease processes in canine.