Other haematological variables in childhood423

There are important differences in the concentration of various clotting factors during early infancy as described on p690. Other laboratory investigations where children differ include:

• Reticulocyte counts low in the first 8 weeks of life as neonatal poly-cythaemia corrects itself.

• HbF comprises 75% of the total Hb at birth, 10% at 5 months, 2% at 1 year and <1% thereafter.

• Some red cell enzymes (G6PD, PK, hexokinase) have greater activity (150-200% of adult values) in neonatal RBC.

• The lower limit of normal for serum ferritin at 1 year (12.5mg/L) is 50% of the LLN at 12 years (25mg/L).

• B12 and folate levels are around 2x higher in infants and younger children than adults.

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