From the Guidelines
Babies do have different normal ranges for white blood cell counts and platelets compared to adults, with newborns typically having higher white blood cell counts and similar platelet counts to adults. Newborns typically have higher white blood cell counts, ranging from 9,000-30,000 cells per microliter at birth, which is significantly higher than the adult normal range of 4,500-11,000, as noted in general medical knowledge. This elevated count gradually decreases over the first few weeks of life. For platelets, however, healthy full-term newborns generally have counts similar to adults (150,000-450,000 per microliter), though they may be slightly lower in the first days of life, as seen in studies such as 1. These differences reflect the developmental changes in the infant's immune and hematopoietic systems. The higher white cell count in newborns serves as a protective mechanism since their immune systems are still immature and developing.
When interpreting blood tests in infants, it's essential to use age-specific reference ranges rather than adult values to avoid misdiagnosis of conditions like leukocytosis or thrombocytopenia, as emphasized by studies on developmental hemostasis, such as 1 and 1. These values continue to change throughout infancy and childhood until reaching adult levels. It's also important to consider the specific analyzer and reagent used in laboratory tests, as population-, reagent-, and analyzer-specific reference ranges are crucial for accurate diagnosis and treatment, as highlighted in 1.
Key points to consider include:
- Newborns have higher white blood cell counts than adults
- Platelet counts in healthy full-term newborns are similar to adults
- Age-specific reference ranges are essential for accurate diagnosis and treatment
- Developmental changes in the infant's immune and hematopoietic systems affect blood cell counts
- Laboratory tests should use population-, reagent-, and analyzer-specific reference ranges, as noted in 1 and 1.
From the Research
White Blood Cell Counts in Babies
- Babies have higher white blood cell counts, with the 50th and 97.5th quantiles of total white blood cell count being highest at birth, then rapidly decreasing in the first 6 months of life 2.
- The pattern of neutrophil count changes with age in a manner opposite to that of lymphocyte count, with two inter-sections of lymphocyte count and neutrophil count during infancy and at approximately 5 years of age 2.
- Newborns delivered vaginally have significantly higher total leukocytes, neutrophils, band forms, and platelets compared to those delivered by Cesarean section 3.
Platelet Counts in Babies
- Platelet counts are also higher in newborns, with a mean of 304 x 10^9 +/- 4.1 per microliter in vaginally delivered babies and 286 x 10^9 +/- 0.6 per microliter in babies delivered by Cesarean section 3.
- Certain antibiotics, such as gentamicin, can affect platelet aggregation and blood coagulation, potentially leading to thrombocytopenia 4, 5.
- White blood cell and platelet counts can be used to differentiate between infection and the normal response after splenectomy, with a WBC greater than 15 x 10/microL and a PC/WBC ratio < 20 on postoperative day 5 being highly associated with infection 6.