Pediatric Blood Volume & Transfusion Volume Calculator

How it works

EBV = weight × mL/kg (preterm 100, term 85, infant 80, child 75, adolescent 70); PRBC volume = EBV × (target Hb − current Hb) ÷ Hb of the unit (≈ Hct ÷ 3); allowable loss = EBV × (Hct − Hct_min) ÷ Hct

Children carry more blood per kilogram than adults — a term newborn about 85 mL/kg, a school-age child 75 — but far less in absolute terms, so a 100 mL loss that an adult would not notice is 7% of a newborn’s volume. Transfusion volumes are therefore calculated, not ordered by the unit: the volume of packed cells needed equals the blood volume times the desired haemoglobin rise divided by the haemoglobin concentration of the bag, which for a typical 60% haematocrit unit is about 20 g/dL. The familiar rule that 10 mL/kg raises haemoglobin by 2–3 g/dL falls out of that formula. Transfusions are usually capped at 15–20 mL/kg per episode to avoid circulatory overload, and given slowly when anaemia is severe. Allowable blood loss guides surgeons on how much bleeding can be replaced with fluid before red cells are needed.

Worked example

A 20 kg child (EBV 1,500 mL) with Hb 6.5 g/dL to a target of 10: a rise of 3.5 g/dL needs 1,500 × 3.5 ÷ 20 = 263 mL of 60% Hct red cells — about 13 mL/kg, given over roughly 3 hours. Ten mL/kg would raise Hb by about 2.7 g/dL. At Hb 6.5 the haematocrit (≈ 20%) is already under a 25% floor, so there is no allowable loss; once at Hb 10 the child could lose about 250 mL before dropping to 25%.

Frequently asked questions