### Description

The amount of blood loss from endometrial bleeding can be estimated by eluting blood from the sanitary pads and measuring the absorbance in a spectrophotometer at 550 nm. This technique can be extended to estimating surgical blood loss from blood collected on surgical pads.

Procedure:

(1) The women were instructed to use both an internal tampon and an external sanitary towel. The tampon was not to be removed while bathing. Removed items were wrapped in aluminum foil, then placed into a plastic freezer bag, which was placed in a freezer at -20°C.

(2) The technique described covered the entire menstrual period. A shorter interval could be used in very heavy endometrial bleeding.

(3) Once the collection period is complete, all of the pads and tampons are washed for 10 minutes in 10 liters of tap water with a nonionic detergent (Triton X-100) at a concentration 0.1% for an average number of pads to 0.2% with a large number of pads.

(4) A 10 mL sample of the washing solution was collected and centrifuged to remove pad debris. 0.5 mL of the supernatant was mixed with 0.5 mL of 0.85 mol/L sodium carbonate.

(5) After waiting 10 minutes to allow conversion of hemoglobin to alkaline haematin, the sample was placed in a spectrophotometer set to 550 nm and the absorbance read.

Estimating Amount of Hemoglobin

A calibration curve of hemoglobin standards in g/L versus absorbance measured at 550 nm should be prepared.

• slope given in Figure 1 page 1030 is 0.33; 1/(slope) = 3.03

• range given in Figure 1 is 0.27 to 0.35; the mean for this range is 0.31; 1/(slope) = 3.225

absorbance at 550 nm =

= (slope) * (hemoglobin in g/L)

Rearranging this equation:

hemoglobin in g/L =

= (absorbance at 550 nm) / (slope)

= (absorbance at 550 nm) * 3.26

where:

• 3.26 is according to Equation (1), page 1030; to get 3.26, the slope would be 0.3067.

In 10 liters of fluid, the total amount of hemoglobin is:

total hemoglobin in 10 L =

= 10 * (hemoglobin in g/L)

Estimating the Amount of Blood Loss

volume of blood loss in mL =

= (total hemoglobin in 10 L) / (hemoglobin concentration in venous blood in g/dL) * 100

where:

• 100 is the conversion from deciliters to milliliters

If the number of hours over which the sample was collected is known, then an estimate of the 24 hour blood loss would be:

estimated 24 hour blood loss in mL =

= 24 / (time period in hours) * (volume of blood loss in mL)

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