Medical Definition of Hematocrit

Hematocrit: The proportion of the blood that consists of packed red blood cells. The hematocrit is expressed as a percentage by volume. The red cells are packed by centrifugation.

For example, an hematocrit of 25% means that there are 25 milliliters of red blood cells in 100 milliliters of blood. The red cells make up a quarter of the blood.

The normal ranges for the hematocrit are dependant on the age and, after adolescence, the sex of the individual. The normal ranges for the hematocrit are:

  • Newborns: 55-68%
  • One (1) week of age: 47-65%
  • One (1) month of age: 37-49%
  • Three (3) months of age: 30-36%
  • One (1) year of age: 29-41%
  • Ten (10) years of age: 36-40%
  • Adult males: 42-54%
  • Adult women: 38-46%

These values may vary slightly between laboratories.

The term "hematocrit" was coined in 1903 and comes from the Greek roots hemat-, blood + krites, judge = to judge or gauge the blood. The abbreviation for hematocrit is hct. In medical slang the hematocrit is called the crit.

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Reviewed on 12/12/2018