Hematocrit is the proportion of erythrocytes in the total volume of blood . It is determined by centrifugation of non-clotting blood. During centrifugation, the erythrocytes are separated from the plasma. The white, opaque layer just above the erythrocytes, sometimes referred to as the buffy coat , is made up of platelets and leukocytes and makes up about 1% of the total blood volume. The resulting hematocrit value is given in % or in ratio numbers. 
When collecting blood for hematocrit, the anticoagulant must not affect the final volume of the sample!
Physiological values of hematocrit
- men: 44±5 % (0,44±0,05)
- women: 39±4 % (0,39±0,04)
The hematocrit value decreases, for example, when the number of erythrocytes decreases, their volume decreases or when the plasma volume increases.
- ŠVÍGLEROVÁ, Jitka. Hematokrit [online]. The last revision 2009-02-18, [cit. 2010-11-11]. <https://web.archive.org/web/20160416224352/http://wiki.lfp-studium.cz/index.php/Hematokrit>.
- TROJAN, Stanislav. Lékařská fyziologie. 4. edition. Prague : Grada Publishing, a.s., 2003. 771 pp. ISBN 80-247-0512-5.