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Definition of Hematocrit

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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.

Reviewed on 12/12/2018

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