Anemia of prematurity pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Pathophysiology
The total volume of blood in premature infants is approximately 100ml/kg of body weight--approximately 5 ounces for a 1.5kg infant. Blood sampling done for laboratory testing in the first days of life can easily remove enough blood to produce anemia. As anemia develops, the amount of oxygen delivered by the hemoglobin in the blood to the body organs declines. Normally this stimulates increased production oferythropoietin (EPO), but this response is diminished in premature infants. While the reason for this decreased response is not fully understood, it is theorized that there is a genetically timed switch from hepatic production of EPO, which occurs in-utero, torenal production. Since hepatic production is stimulated by lower levels of oxygen delivery (reflecting the lower levels present in the fetus) and since the red blood cells are carrying higher amounts of oxygen after birth, the level of red blood cells itself must drop significantly before EPO production will begin in premature infants who have not yet switched from hepatic to renal EPO production. This level may be as low as a hemoglobin of 6.5g/dL, corresponding to an hematocrit of approximately 19.