Differential diagnosis of microcytic hypochromic anemia in dogs: the role of hepcidin and reticulocyte hemoglobin indices.

Microcytic hypochromic anemia in dogs represents a persistent diagnostic challenge, particularly when differentiating between absolute iron deficiency and inflammation-driven functional iron restriction. Conventional biomarkers, including serum iron and ferritin, present important limitations in terms of sensitivity, specificity, and temporal resolution, restricting their ability to accurately reflect dynamic changes in iron metabolism. This review critically evaluates the diagnostic performance and clinical relevance of hepcidin and reticulocyte hemoglobin indices (CHr/RET-He) as advanced biomarkers of iron-restricted erythropoiesis in dogs. Reticulocyte indices provide a dynamic and near real-time assessment of iron availability at the level of erythropoiesis, enabling early detection of iron-restricted states and monitoring of therapeutic response. However, their diagnostic utility is limited by an inability to discriminate between underlying etiological mechanisms. In contrast, hepcidin, the central regulator of systemic iron homeostasis, provides mechanistic insight into iron metabolism. Its circulating concentrations decrease in absolute iron deficiency and increase in inflammation-mediated iron sequestration, thereby potentially facilitating etiological differentiation. Despite its diagnostic potential, clinical application remains limited by methodological variability, lack of assay standardization, and incomplete reference intervals in canine populations. The integration of functional biomarkers (CHr/RET-He) with a regulatory biomarker (hepcidin) is proposed as a complementary and physiologically grounded approach. This combined strategy may enhance diagnostic accuracy, support etiological classification, and facilitate clinical decision-making; however, its diagnostic performance has not yet been sufficiently validated in canine patients, and further prospective studies are required before routine clinical implementation can be recommended.