Normal CBC Ranges for Newborns
Normal CBC values in newborns vary significantly based on gestational age, postnatal age, and whether the infant is appropriate-for-gestational-age (AGA) or small-for-gestational-age (SGA), with reference ranges being substantially different from older children and adults. 1
Hemoglobin and Hematocrit Reference Ranges
Term Newborns (≥37 weeks gestation)
- Hemoglobin at birth: Approximately 16-20 g/dL for AGA infants 2
- Hematocrit at birth: Approximately 48-60% for AGA infants 2
- SGA term infants have higher values: Mean hemoglobin, hematocrit, and RBC counts are elevated compared to AGA infants on day 1 of life 3
Preterm Newborns (<37 weeks gestation)
- Lower hemoglobin values than term infants, with values decreasing as gestational age decreases 2
- Mean corpuscular volume (MCV) is higher in preterm AGA newborns compared to term AGA newborns 2
- Reference ranges depend on both gestational age (22-42 weeks) and postnatal age (0-29 days), requiring mathematical modeling for accurate interpretation 4
Postnatal Changes
- Hemoglobin and hematocrit values remain relatively stable in the first two weeks for term and late preterm neonates 5
- Preterm neonates may show increases in upper reference limits, particularly if receiving erythrocyte transfusions 5
Red Blood Cell Indices
Red Cell Distribution Width (RDW)
- At birth for term/late preterm: Lower reference limit is 15.5%, upper limit is 20% 5
- For preterm neonates: Upper reference limit is slightly higher, up to 23% 5
- High RDW values (29.4-42.8%) indicate anisocytosis, commonly due to prenatal hemorrhage or hemolysis 5
- Low RDW values (11.8-13.7%) correlate with relative microcytosis 5
Mean Corpuscular Volume (MCV)
- SGA newborns have decreased MCV relative to their elevated RBC count 3
- Mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) are also decreased in SGA babies due to relatively high RBC counts 3
White Blood Cell Parameters
Lymphocyte Counts
- Lymphopenia threshold in infants <8 months: <4,500/mm³, which is substantially higher than the adult threshold of <1,500/mm³ 6
- Premature infants may have lower lymphocyte counts as an isolated finding without pathology 6
- T-cell counts <1,500/mm³ in the context of suspected immunodeficiency warrant further evaluation with flow cytometry 6
Neutrophil Counts
- SGA newborns have higher rates of neutropenia: 21.9% had neutropenia and 4.7% had absolute neutrophil counts <1,500/μL on day 1 3
- Higher mean absolute metamyelocyte counts and higher immature-to-total neutrophil (I:T) ratios in SGA newborns on both day 1 and day 7 compared to AGA infants 3
Lymphocyte Count Changes
- SGA babies have lower mean absolute lymphocyte counts on day 7 compared to AGA infants 3
Platelet Parameters
Platelet Counts
- Thrombocytopenia is common in SGA newborns: Detected in almost one-third of SGA newborns tested on day 1 3
- Platelet levels are reduced in SGA newborns compared to AGA newborns 2
Other Red Cell Parameters
Normoblast Count
- Higher mean normoblast counts in SGA babies compared to AGA babies on day 1 3
Reticulocyte Correlation
- RDW and reticulocyte counts correlate positively but weakly (r² = 0.187) 5
- High RDW values at birth commonly indicate macrocytic reticulocytosis 5
Important Clinical Considerations
Gestational Age-Specific Differences
- Preterm SGA infants are truly growth restricted, whereas term SGA infants are most likely small but otherwise healthy babies, as evidenced by their hematologic parameters 2
- Each neonatal medical unit should establish its own reference ranges, as values can vary based on local population characteristics and laboratory methods 2
Interpretation Pitfalls
- Do not use adult or pediatric reference ranges for neonates, as this will lead to misclassification of normal values as abnormal 1
- Both gestational age and postnatal age are independent factors determining hemoglobin and hematocrit levels and must be considered simultaneously 4
- SGA status significantly alters CBC parameters, with differences in MCV, MCH, MCHC, metamyelocyte counts, lymphocyte counts, and I:T ratios compared to AGA babies 3