NRBC (Nucleated Red Blood Cells): Definition and Clinical Significance
NRBCs are immature red blood cell precursors that normally reside in the bone marrow and are not present in the peripheral blood of healthy adults, though they can be found in fetuses and neonates. 1
Basic Definition
- NRBCs are normoblastic cells that failed to extrude their nuclei before exiting from bone marrow or liver 2
- These are premature erythrocyte precursors that are part of normal erythropoiesis but should remain confined to the bone marrow in healthy adults 1
- In contrast to mature red blood cells, which are non-nucleated and organelle-free, NRBCs retain their nucleus 3
Normal vs. Abnormal Presence
- NRBCs are normally absent in the peripheral blood of healthy adults 1, 4
- They are physiologically present in fetal circulation and neonates 1
- Their appearance in adult peripheral blood indicates extremely high demand for RBC production, causing premature release of immature cells into circulation 4
Clinical Conditions Associated with NRBCs
When NRBCs appear in peripheral blood, they indicate:
- Severe hypoxemia and tissue hypoxia 5
- Placental dysfunction and fetal asphyxia (in neonates) 5
- Anemia and hemolytic disorders 1
- Myelofibrosis and bone marrow malignancies (myelomas, leukemias, lymphomas) 4
- Thalassemia 4
- Prolonged hypoxemia 4
- Sepsis and critical illness 4
Prognostic Significance
The presence of NRBCs in peripheral blood is strongly associated with increased mortality and adverse outcomes in critically ill patients:
- In ICU patients, NRBC presence carries a 30% mortality rate compared to 14% in NRBC-negative patients 4
- A cutoff of ≥2.5 NRBCs/100 WBC shows 91% sensitivity for predicting mortality risk 4
- In neonates post-cardiac surgery, NRBC ≥10/100 WBC has 88.9% sensitivity and 90.8% specificity for mortality prediction 6
- In very low birth weight infants, an increase of 10/nL in mean NRBC count on postnatal days 2-5 carries an odds ratio of 6.95 for mortality 2
Clinical Utility
- NRBC count is a cost-effective laboratory test that can be obtained from routine complete blood counts 1
- Persistence of elevated NRBCs beyond day 3-4 of life in neonates is an independent predictor of adverse outcomes 5
- In critically ill adults, NRBC presence indicates disease severity and helps stratify mortality risk 4
- The test is particularly valuable for monitoring preterm infants with growth restriction, neonatal hypoxia, and asphyxia 1, 5