Blood Volume in Adult Patients

Estimation of Blood Volume

The average blood volume in adult patients is approximately 70 mL/kg of body weight, resulting in a total blood volume of around 4,900 mL for a 70 kg individual, according to the American College of Physicians 1
Blood volume consists of red blood cells and plasma volume, which together form the total blood volume, as stated by the National Kidney Foundation 2

In adult males (>18 years, 70 kg), the blood volume is approximately 70 mL/kg, resulting in a total volume of around 4,900 mL, as reported by the American College of Physicians 1
In adolescent males (11-18 years, 35-65 kg), the blood volume ranges from 70-75 mL/kg, resulting in a total volume of approximately 2,600-4,500 mL, according to the American College of Physicians 1
In children (2-11 years, 12-35 kg), the blood volume is approximately 75 mL/kg, resulting in a total volume of around 900-2,600 mL, as stated by the American Academy of Pediatrics 1
In older infants (0.5-2 years, 7.5-12 kg), the blood volume is approximately 75-80 mL/kg, resulting in a total volume of around 600-900 mL, according to the American Academy of Pediatrics 1
In younger infants (0-6 months, 3.5-7.5 kg), the blood volume is approximately 80-85 mL/kg, resulting in a total volume of around 300-600 mL, as reported by the American Academy of Pediatrics 1
In newborns (3.5 kg), the blood volume is approximately 85 mL/kg, resulting in a total volume of around 300 mL, according to the American Academy of Pediatrics 1

Adult ICU patients lose approximately 340-660 mL of blood per week for diagnostic testing, as reported by the Society of Critical Care Medicine 3, 4
The average blood loss for diagnostic testing is approximately 77.8 mL/day, according to the Society of Critical Care Medicine 4
Hemodialysis patients lose approximately 15-25 mL of whole blood per dialysis session (around 60 mL per week), as stated by the National Kidney Foundation 2

A hematocrit of 25% with a blood volume of 5,600 mL results in a red blood cell volume of 1,400 mL, according to the National Kidney Foundation 2
A hematocrit of 35% with the same blood volume results in a red blood cell volume of 2,000 mL, as reported by the National Kidney Foundation 2
To increase the hematocrit from 25% to 35% in a 70 kg patient, approximately 600 mL of new red blood cells are required, which necessitates 600 mg of iron, according to the National Kidney Foundation 2

Ongoing occult blood loss contributes to increased variability in the hematocrit response to acute blood loss, with observed changes ranging roughly from 1 % to 5 % for the same volume of loss in adult patients【5】.

Clinical guidelines published in Anaesthesia advise that blood‑conserving measures should be implemented when cumulative diagnostic or therapeutic blood loss exceeds 500 mL or 10 % of a patient’s calculated total blood volume, because this threshold is associated with a clinically meaningful decline in hematocrit【6】.