Anaemia of Prematurity
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Direct answer
Anaemia of prematurity is the normocytic anaemia that preterm infants develop as haemoglobin falls to a physiological nadir, usually around 6 to 8 weeks of age. It results from a shortened red cell lifespan, a blunted erythropoietin response, rapid growth and blood lost to frequent sampling. Most babies need careful blood conservation and iron, with transfusion reserved for defined thresholds and clinical signs.
What you must remember
- Physiological nadir: haemoglobin falls over the first months of life and reaches its lowest point around 6 to 8 weeks.
- Shortened red cell lifespan: preterm red cells survive for a shorter time, so haemoglobin is lost faster than it is replaced.
- Blunted erythropoietin: levels are lower than expected for the degree of anaemia, so the marrow responds weakly.
- Iatrogenic loss: frequent phlebotomy is a major and avoidable contributor, especially in ventilated infants.
- Iron: stores are low in very preterm babies, so iron supplementation is usually started by around 2 to 4 weeks of age, per unit protocol.
- Transfusion thresholds: depend on postnatal age, clinical state and whether the baby is ventilated or septic, and are higher in sick infants.
- Erythropoietin: used selectively, with mixed evidence for reducing transfusion, so it is not routine for all preterm infants.
A graded approach to transfusion
The decision to transfuse is taken on the baby's haemoglobin together with clinical signs, rather than on haemoglobin alone. The steps below reflect the usual reasoning on neonatal units, though the exact thresholds are set by local guidelines.
- Confirm the anaemia: check haemoglobin and reticulocyte count to separate physiological anaemia from haemolysis or bleeding.
- Assess clinical state: look for tachycardia, apnoea, poor weight gain and feeding intolerance, which suggest the anaemia is causing harm.
- Check the threshold: compare haemoglobin with the threshold for the baby's postnatal age and clinical state, since thresholds are higher in ventilated or septic infants.
- Reduce losses: cut phlebotomy volumes and cluster blood tests, since iatrogenic loss is a major contributor to the anaemia.
- Give iron and nutrition: start iron supplementation and ensure adequate feeds, following unit protocol.
- Transfuse if indicated: give packed red cells in small aliquots, with close monitoring of volume status and vital signs.
Where the exam tries to catch you
Anaemia of prematurity questions test the physiology of the nadir and the logic of transfusion.
- Trap: transfusing for any low haemoglobin value. Correct: transfusion is guided by thresholds, clinical signs and postnatal age, not by haemoglobin alone.
- Trap: assuming erythropoietin is always needed. Correct: erythropoietin use is selective, and evidence for reducing transfusion is mixed, so it is not a routine intervention.
- Trap: attributing all preterm anaemia to nutrition. Correct: it is mainly due to shortened red cell survival and a blunted erythropoietin response, with iatrogenic losses adding to it.
Frequently asked questions
What causes anaemia of prematurity?
Anaemia of prematurity is caused by a shortened red cell lifespan, a blunted erythropoietin response, rapid growth and iatrogenic blood loss from frequent sampling. Low iron stores in very preterm babies add to the problem. The anaemia is usually normocytic and reaches its lowest point around 6 to 8 weeks.
Why is the erythropoietin response reduced in preterm infants?
The erythropoietin response is reduced in preterm infants because erythropoietin production is lower than expected for the degree of anaemia. The marrow therefore responds less than it would in a term baby with the same haemoglobin. This blunted response is a central feature of anaemia of prematurity.
What haemoglobin level prompts transfusion in preterm babies?
Transfusion in preterm babies is guided by haemoglobin thresholds that depend on postnatal age, clinical state and whether the baby is ventilated or septic. Thresholds are higher in sick or ventilated infants. Transfusion decisions also weigh symptoms such as tachycardia, apnoea and poor weight gain.
Does erythropoietin prevent anaemia of prematurity?
Erythropoietin is used selectively to reduce transfusion needs in anaemia of prematurity, but the evidence for a clear benefit is mixed. It is not a routine intervention for all preterm infants. Iron supplementation and minimal blood sampling remain the mainstays of prevention in most units.