Landsfeld et al used an equation for estimating blood loss in the Bleeding Severity Index.

amount of blood loss in units of blood =

= (number of units transfused) + (((hematocrit initial in percent) – (hematocrit after in percent)) / 3) – ((estimated surgical blood loss in mL) / 400)



• The original equation had the hematocrit divided by 0.03, which would mean that the hematocrits would be as decimal fractions.

• Dividing the hematocrit by 3 (preferably 2.941) gives the hemoglobin in g/dL.

• As a rough rule of thumb, 1 unit of blood will raise the hemoglobin by 1 g/dL.

• The 400 factor is an estimate for the volume of 1 unit whole blood. 1 unit of whole blood may vary in volume from 405 – 495 ml (AABB Technical Manual).


Blood Loss in Units


>= 3 units


2 to < 3 units


1 to < 2 units




• Categories for minimal and massive blood loss could probably also be defined.

• The hematocrit would be affected by hemoconcentration and hemodilution.

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