Red blood cell indices: Implications for practice

The first few weeks to months of life are characterized by dramatic physiologic and anatomic changes. As hematologic parameters are evolving during this time period, laboratory data must be assessed in light of the ongoing developmental adjustments that are taking place. Fetal and neonatal erythrocytes differ significantly from those produced by older infants, children, and adults. They are larger in size, have a shorter life span, altered shape and deformability, and high fetal hemoglobin concentrations. While these differences do not impact their ability to deliver oxygen to the tissues to meet their metabolic needs, these characteristics may confound the interpretation of hematologic data and complicate the diagnosis of neonates with certain disorders such as anemia. RBC indices such as mean corpuscular volume, mean corpuscular hemoglobin concentration, and red cell distribution width are laboratory parameters that are frequently overlooked in clinical practice but they can provide assistance in establishing a diagnosis in anemic patients.