he·​mat·​o·​crit hi-ˈma-tə-krət How to pronounce hematocrit (audio)
: the ratio of the volume of red blood cells to the total volume of blood as determined by separation of red blood cells from the plasma usually by centrifugation

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Our blood is mostly made up of four components: plasma, red blood cells, white blood cells, and colorless blood cells called platelets. An instrument called a hematocrit (because it "judges" the blood) is used to separate a sample of blood into its components. The normal hematocrit for men is about 48%, for women about 38%. An abnormal proportion of red blood cells, either too many or too few, is a good early indicator of many diseases. So when you give blood as part of a physical exam, your hematocrit is one of the findings your doctor will often check.

Example Sentences

Recent Examples on the Web Blood samples showed that their hematocrit levels—a measure of red blood cells, which carry oxygen—had also increased. Elizabeth Preston, Discover Magazine, 27 Jan. 2015 Lundby’s hypothesis is based on the idea that your kidneys are constantly monitoring hematocrit, trying to keep it in a normal range. Alex Hutchinson, Outside Online, 1 July 2020 However, if the liquid portion is greatly increased through training, the proportion that makes up the hematocrit will decrease accordingly, falsely suggesting anemia. Bryant Stamford, The Courier-Journal, 28 Apr. 2022 If your total blood is made up of 45 percent red blood cells by volume, your hematocrit is 45. Alex Hutchinson, Outside Online, 1 July 2020 If heat training causes your plasma volume to increase, that will lower your hematocrit. Alex Hutchinson, Outside Online, 1 July 2020 Typically, the ratio of solids in the blood (RBCs, white blood cells and platelets called the hematocrit) to the liquid portion is approximately 50-50. Bryant Stamford, The Courier-Journal, 28 Apr. 2022 His complete blood count, to include his white blood cell count, his hemoglobin, hematocrit, and platelet count were all normal. Jamie Ducharme, Time, 18 Jan. 2018 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'hematocrit.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


International Scientific Vocabulary hemat- + Greek kritēs judge, from krinein to judge — more at certain

First Known Use

circa 1903, in the meaning defined above

Time Traveler
The first known use of hematocrit was circa 1903

Dictionary Entries Near hematocrit

Cite this Entry

“Hematocrit.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/hematocrit. Accessed 2 Jun. 2023.

Medical Definition


variants or chiefly British haematocrit
: an instrument for determining usually by centrifugation the relative amounts of plasma and corpuscles in blood
: the percent of the volume of whole blood that is composed of red blood cells as determined by separation of red blood cells from the plasma usually by centrifugation
a hematocrit ranging from 42% to 52% in males and 35% to 47% in females is typically considered normal

called also packed cell volume

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