Allowable Blood Loss Calculation Formula

Assessment of blood loss during surgery is an integral part of anesthesia practice. However no accurate and practical methods or tests are available for measuring blood loss during surgery. 

There are few methods for calculation of blood loss like gravimetry, photometry and serial Hb measurement. These methods have limited use in practice because of unavailability and time consumption. Hence visual observation is the most commonly used method for estimating blood loss.

Allowable blood loss (ABL) = EBV X [(Hi – Hf) ÷ Hi] 


EBV = Estimated Blood Volume

Hi = Initial hematocrit 

Hf = Final hematocrit

Estimated Blood Volume (EBV) Calculation:

EBV = Weight (kg) X Blood volume (age and gender)  

Normal Blood volume based on age and gender:

  • Premature Neonate - 95 ml/Kg
  • Full term Neonate - 85 ml/Kg
  • Infant - 80 ml/Kg
  • Adult Male - 75 ml/Kg
  • Adult Female - 65 ml/Kg

For example,

60 kg female with pre-operative hematocrit of 45%. How much is the allowable blood loss for the final or the targeted hematocrit of 30%?

Step 1: EBV = 60 (weight in Kg) X 65 (Blood volume in females)

EBV = 3900 ml.

Step 2: Allowable blood loss (ABL) = EBV X [(Hi – Hf) ÷ Hi]

 ABL = 3900 X [(45 – 30) ÷ 45]

 ABL = 1300 ml

Here the allowable blood loss is 1300 ml.  

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