Allowable Blood Loss Calculator
The allowable blood loss calculation is an essential part of the pre-surgery routine. It estimates how much blood a patient can lose before reaching a dangerously low level of hemoglobin. In this article, you can find information on what is the maximum allowable blood loss and what formula we use.
We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace a professional doctor's assessment. All information on this website is for informational purposes only and is not intended to serve as a substitute for medical consultation. Always consult your results with a healthcare provider.
How to use the allowable blood loss calculator
sex/age categoryof the patient – the calculator uses several different coordinates, whether they're a newborn baby or an adolescent male.
weightin the preferred unit – our calculator converts it to kilograms by itself.
hemoglobin(Hgb) level in g/dL.
lowest allowable hemoglobinlevel – depending on the patient, it's usually between 7 and 10 g/dL.
The allowable blood loss is calculated in mL, but you can switch to other units just by clicking on the unit.
What is the allowable blood loss formula?
Here, the blood volume is already included in the equation:
ABL = weight (kg) × age_sex_factor × [initial_hemoglobin (g/dL) − final_hemoglobin (g/dL)] / initial_hemoglobin (g/dL)
age_sex_factor is the amount of blood per kilogram of body weight for the chosen category. It is estimated approximately as:
- 100 mL/kg for premature infants;
- 85 mL/kg for babies younger than 3 months;
- 75 mL/kg for children over the age of 3 months;
- 70 mL/kg for male adolescents;
- 65 mL/kg for female adolescents and adults; and
- 75 mL/kg for male adults.
What is the maximum allowable blood loss volume?
For example, for a relatively healthy adult male with a hemoglobin level of 15 g/dL and 80 kg of weight, the allowable blood loss would be around 2,400 ml, whereas, for a teenager with a hemoglobin level of 12 g/dL and 60 kilograms of weight, it would only be 1,050 ml.
According to Morgan and Mikhail's Clinical Anesthesiology:
“Ideally, blood loss should be replaced with crystalloid or colloid solutions to maintain intravascular volume (normovolemia) until the danger of anemia outweighs the risks of transfusion. At that point, further blood loss is replaced with transfusions of red blood cells to maintain hemoglobin concentration (or hematocrit) at that level. For most patients, that point corresponds to a hemoglobin between 7 and 10 g/dL or a hematocrit of 21-30%.”