Pathophysiology of Anemia During the Neonatal Period, Including Anemia of Prematurity

Abstract

This review summarizes the current thinking about the causes of anemia universally experienced by preterm infants in the early postnatal weeks. In addition to describing developmentally determined physiologic processes contributing to anemia of prematurity, this review discusses clinically important nonphysiologic contributors to anemia experienced by preterm infants during the neonatal period. Chief among these and an important contributor to the need for red blood cell transfusions is the heavy laboratory phlebotomy loss sustained shortly after birth, when neonatal cardiorespiratory illness is most severe. Understanding and recognizing the physiologic and nonphysiologic processes contributing to anemia encountered in early postnatal life is important in knowing which treatment and prevention modalities are likely to be most effective in different clinical situations. The evaluation of rare and uncommon acquired and genetic causes of anemia in newborns are not covered in this review.

Figures

Figure 1

Hemoglobin concentrations and reticulocyte counts in preterm and term infants during the first 6 postnatal months. Median values and 95% confidence limits are indicated for each of three birthweight groups represented. Reprinted with permission from Dallman PR. Anemia of prematurity. Ann Rev Med. 1981;32:143–160.

Figure 2

Pathophysiology of neonatal anemia. Contributors to anemia that develops during the neonatal period include physiologic and nonphysiologic factors. Physiologic factors that are developmentally regulated are viewed as likely contributors to anemia of prematurity. Those that are nonphysiologic are acquired and are more amenable to intervention; some are iatrogenic. The contributors included in the figure are operative at varying times, depending on the developmental and clinical circumstances, with many occurring simultaneously. The effect of each on the severity of anemia varies. During the first postnatal weeks, when severe neonatal cardiorespiratory illness is at its peak and frequent laboratory testing is most intense, phlebotomy loss among preterm infants is typically the most important contributor to neonatal anemia and the need for red blood cell transfusion. EPO=erythropoietin, ODC=oxygen dissociation curve, RBC=red blood cell