Calc Function

    • Calcs that help predict probability of a diseaseDiagnosis
    • Subcategory of 'Diagnosis' designed to be very sensitiveRule Out
    • Disease is diagnosed: prognosticate to guide treatmentPrognosis
    • Numerical inputs and outputsFormula
    • Med treatment and moreTreatment
    • Suggested protocolsAlgorithm





    Chief Complaint


    Organ System


    Patent Pending

    Maximum Allowable Blood Loss (ABL) Without Transfusion

    Estimates the maximum allowable blood loss intraoperatively before transfusion should be considered.
    When to Use
    Why Use

    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.
    • 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.

    Point to Keep in Mind

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

    Helps with determining when to transfuse a patient if blood count values are not immediately available.



    Please fill out required fields.

    Next Steps
    Creator Insights


    • 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.


    ABL = [EBV x (Hi-Hf)]/Hi, where EBV = body wt (kg) x average blood volume (mL/kg)

    ABL, allowable blood loss. EBV, estimated blood volume. Hi, initial hemoglobin. Hf, final hemoglobin (cutoff for transfusion)


    Evidence Appraisal

    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.

    Jeffrey B. Gross, MD

    About the Creator

    Jeffrey B. Gross, MD, is a professor of medicine and and chair of the department of anesthesiology at the the University of Connecticut. He is currently the chairman of the Task Force on Perioperative Management of Patients with Obstructive Sleep Apnea for the American Society of Anesthesiologists. Dr. Gross is an active researcher investigating novel methods in management in anesthesia.

    To view Jeffrey B. Gross, MD's publications, visit PubMed

    Content Contributors
    • Amit Patel, MD
    About the Creator
    Jeffrey B. Gross, MD
    Content Contributors
    • Amit Patel, MD