How is the hematocrit (Hct) measured?

By William Aird

1) Spun hematocrit:

Anticoagulated blood is drawn into a microtube and the sample is centrifuged (spun) on a tabletop device. Red cells gravitate to the bottom, plasma settles on the top. The tube is then placed vertically and the heights of the red cell column and the red cell + plasma column are measured. The Hct is the height of the red cell column divided by the total height of red cell + plasma columns.

2) Calculated from mean cell volume (MCV) and red blood cell (RBC) count:

Hct = MCV x RBC count

For example:

0.45 (45%) = (90 x 10-15L) x (5 x 1012/L)