Maximum Allowable Blood Loss (ABL) Without Transfusion: Online calculator

Maximum Allowable Blood Loss (ABL) Without Transfusion formula can be used in patients with blood loss, typically during surgery, who may need transfusion. The Maximum Allowable Blood Loss Without Transfusion calculator suggests how much blood can be lost, typically during surgery, before transfusion should be considered.



Hemoglobin initial

Hemoglobin final (lowest acceptable hemoglobin, by clinical judgment units)

* Required

Maximum Allowable Blood Loss (ABL) Without Transfusion formula helps with determining when to transfuse a patient if blood count values are not immediately available.

Maximum Allowable Blood Loss (ABL) Without Transfusion calculated based on formula:

ABL = [EBV x (Hi-Hf)] / Hav, where EBV = body weight, kg x average blood volume*, mL/kg and other variables are as follows:

ABLAllowable blood loss
EBVEstimated blood volume
HiInitial hemoglobin
HfFinal hemoglobin (cutoff for transfusion)
HavAverage of initial and final hemoglobin

*Average blood volume by age:

AgeAverage blood volume, mL/kg
Adult man75
Adult woman65
Premature neonate96

Transfusion triggers vary by patient and clinical presentation.

Patients with hemoglobin concentrations below 6 g/dL almost always require transfusion. In stable patients with hemoglobin values 6-10 g/dL, the decision whether to transfuse is based on an evaluation of clinical status; patients with values above 10 g/dL rarely require transfusion unless they are unstable or have signs/symptoms consistent with continued hemorrhage.

During blood loss, dilution of remaining hemoglobin occurs as intravascular volume is maintained by fluid shifts and administration of fluids. Consider transfusing if estimated blood loss exceeds calculated allowable blood loss.

Estimating blood loss intraoperatively can be done via direct measure of blood in suction canister along with measuring soiled sponges.

This method is only an estimate to measure blood loss. Patient vitals and clinical signs should be evaluated clinically first.

Capacity by sponge type:

  • 4x4s: ~10 mL blood
  • Gauze sponges (Ray-Tec):~10-20 mL blood
  • Laparotomy (lap) sponges: ~50-100 mL blood

Consider timing of blood loss. Acute blood loss may not present with a drop in hemoglobin. Always monitor clinical metrics such as hemodynamics and respiratory status along with anticipated blood loss.

The trigger to transfuse varies by patient.

The maximum allowable blood loss equation was developed by Jeffrey Gross based on an accepted equation for blood loss and incorporating a correction for isovolumetric hemodilution using a mathematical differential.

Gross in 1983 showed that a blood loss greater than 20% of estimated blood volume will cause the maximum allowable value to be inaccurate.

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  1. Gross JB. Estimating Allowable Blood Loss Corrected for Dilution. Anesthesiology 58.2 (1983): 277-280.
  2. Practice Guidelines for blood component therapy: A report by the American Society of Anesthesiologists Task Force on Blood Component Therapy.
  3. Practice guidelines for blood transfusion: a compilation from recent peer-reviewed literature. American Red Cross.

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