Allowable Blood Loss Calculator

What Is Allowable Blood Loss?

Allowable blood loss (ABL) estimates how much blood a patient can lose before hemoglobin falls below a target level. Surgeons use it to plan transfusion thresholds during procedures. Related tools: Blood Donor Calculator and Adjusted Body Weight Calculator.

Allowable Blood Loss Formula

$$\mathrm{ABL} = \mathrm{weight} \times f \times \frac{H_{\mathrm{initial}} - H_{\mathrm{final}}}{H_{\mathrm{initial}}}$$

Weight is in kilograms. $f$ is the blood volume factor in mL/kg, which varies by patient category. Hemoglobin values are in g/dL. The result is in milliliters.

Patient Category Factors

Adult males use 75 mL/kg. Adult females use 65 mL/kg. Children and babies use higher factors because their blood volume per kilogram is greater. Premature infants use 100 mL/kg.