It is normal and expected for newborns to have an elevated RBC count, hemoglobin (HGB), and hematocrit (HCT). This is due to increased erythropoietin (EPO), a hormone produced by the kidneys. EPO stimulates the hematopoietic stem cells (HSCs) in the bone marrow to mature into RBCs. EPO is normally increased at birth due to the low-oxygen environment present during intrauterine life, thus accounting for the increased RBC, HGB, and HCT seen on newborn complete blood counts.
After birth, the newborn is exposed to higher amounts of oxygen in the environment and EPO production decreases. Less of the EPO hormonal signal is received by the bone marrow and HGB levels can drop over the first three months to an average of 11 g/dL but possibly down to 9 g/dL. This decrease is normal and is termed the physiologic anemia of infancy. No treatment is required.
For newborns born prematurely (before 32 weeks of gestation), the innate ability to increase EPO is less than that of a mature newborn. Premature newborns are already predisposed to having a lower HCT at birth and this inability to increase EPO limits their capacity to respond appropriately after birth. Anemia of prematurity will typically present between one to three months after birth in a premature infant.
Some infants with this condition may remain asymptomatic, while others experience tachycardia (increased heart rate) or bradycardia (decreased heart rate), decreased weight gain, decreased oxygenation, and stoppage of breathing (apnea). Normocytic normochromic anemia will be seen on the peripheral blood smear. HGB, HCT, reticulocyte count, and serum EPO will all be low.
Iron supplementation is important in the management of these patients and laboratory testing should be limited to reduce iatrogenic losses that would contribute further to the anemia.
