Diagnosis of Anemia of Prematurity

In adults and babies alike, new red blood cells are constantly being produced and old ones broken down in the body. The production of red blood cells (RBCs) is initiated by a hormone called erythropoietin or EPO. When a baby is born, the production of EPO tends to drop off slightly and there is a corresponding drop in the production of RBCs. This process is the cause of the condition known as the physiological anemia of infancy.

Since the production of RBCs happens in cycles and newborn babies are only beginning this cyclical process, diagnosing anemia is not as simple as counting RBCs in a blood test. Typically, a premature baby will have a normal drop in RBCs a few days or weeks after birth. Additionally, premature babies often need to have blood taken for other tests, sometimes frequently. Although the amount of blood taken from a newborn baby will be the absolute minimum, anemia can be caused or can be made more severe simply by this process of taking blood.

How anemia of prematurity is diagnosed

Over a period of weeks, a premature baby with anemia of prematurity will likely appear pale and lethargic, though occasionally there will be no symptoms. Blood work will be obtained, specifically a hemoglobin level and a reticulocyte count, which gives an indication of how fast RBCs are being produced and released from the bone marrow.

Anemia can have several causes, including sudden blood loss, increased destruction and reduced production of RBCs, and so other tests will be done to determine the specific cause of a baby’s anemia. Increased destruction of RBCs may occur if the mother and baby’s blood groups are not compatible. This process is known as hemolysis and the condition is called hemolytic anemia. Other causes of hemolysis include abnormally shaped RBCs and missing enzymes within the RBC. Reduced production of RBCs may be acquired due to a lack of iron or vitamins B6 or B12.   At times, it may just be that the baby is undergoing a period of rapid growth and the production of RBCs has yet to catch up with the increasing size of the baby’s body. The very rare congenital anemias are another cause of reduced RBC production.

More information

Andrew James, BSc, MBChB, FRACP, FRCPC

Aideen Moore, MD, FRCPC, MRCPI, MHSc