In a patient with gross hematuria the height of erythrocytes in a spun urine sample can give an indication of the amount of blood loss. This is similar to the hematocrit done on the peripheral blood.
Specimen: a urine specimen that is well mixed
Test: Pipette a sample of urine into a narrow tube and centrifuge so that that erythrocytes are packed in the bottom of the tube.
percent erythrocytes in urine =
= (height of erythrocytes in mm) / (total height of the specimen in mm) * 100%
volume of erythrocytes in the urine in mL =
= (total urine volume in mL) * (percent erythrocytes)
volume of blood loss in mL =
= (volume of erythrocytes in the urine) / (hematocrit in the peripheral blood)
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