Allowable Blood Loss
Input patient weight, population category, initial hematocrit, and minimum acceptable hematocrit to estimate allowable blood loss before transfusion is considered.
Use for non-obese adult males.
Set transfusion trigger or target hematocrit.
Estimated blood volume
4900 mL
Allowable blood loss
1225 mL
Allowable blood loss
1.23 L
How to Use This Calculator
Estimate blood volume
Choose the population category that best fits the patient and input actual body weight. Consider adjusting for obesity using lean body weight when appropriate.
Define hematocrit thresholds
Enter baseline hematocrit and minimum acceptable value (transfusion trigger). Values must satisfy minimum < starting.
Use ABL for intraoperative planning
Compare actual blood loss to allowable limit and guide fluid or transfusion strategies. Reassess with updated labs during surgery.
Formula
Estimated blood volume (EBV) = Weight (kg) × Population factor (mL/kg)
Allowable blood loss (ABL) = EBV × (Starting Hct − Minimum Hct) ÷ Starting Hct
Population factors: Adult male 70 mL/kg, adult female 65 mL/kg, child 80 mL/kg (adjust as needed).
Full Description
Allowable blood loss quantifies the volume of blood a patient can lose before reaching a transfusion threshold. It uses estimated blood volume derived from weight and demographics, along with desired hematocrit limits. Anesthesiologists and surgeons employ ABL to manage intraoperative blood loss, plan for cell salvage, and determine transfusion timing. Adjust calculations based on actual lab trends, hemodynamics, and institutional protocols.
Frequently Asked Questions
Should I use lean body weight?
For obese patients, consider lean body weight or adjusted factors to avoid overestimation of blood volume.
Can I calculate using hemoglobin instead of hematocrit?
Yes. Convert hemoglobin values to hematocrit approximately by multiplying Hb × 3 (e.g., Hb 12 g/dL ≈ Hct 36%).
How often should I reassess ABL?
Update the calculation whenever laboratory values change significantly or when actual blood loss approaches the allowance.
Does this replace clinical judgment?
No. Use ABL as a planning tool alongside hemodynamic monitoring, lab values, and institutional transfusion policies.