he·​mo·​glo·​bin ˈhē-mə-ˌglō-bən How to pronounce hemoglobin (audio)
: an iron-containing respiratory pigment of vertebrate red blood cells that consists of a globin composed of four subunits each of which is linked to a heme molecule, that functions in oxygen transport to the tissues after conversion to oxygenated form in the gills or lungs, and that assists in carbon dioxide transport back to the gills or lungs after surrender of its oxygen
: any of numerous iron-containing respiratory pigments of various organisms (such as invertebrates and yeasts)

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When filled with oxygen, the hemoglobin in your blood is bright red; returning to the lungs without its oxygen, it loses its brightness and becomes somewhat bluish. Hemoglobin levels can change from day to day, and may be affected by such factors as a lack of iron in the diet, a recent loss of blood, and being pregnant. When you give blood, a nurse first pricks your finger to test your hemoglobin level; a low hemoglobin count indicates anemia and may mean that you shouldn't give blood that day. Mild anemia is generally of little importance, but some types can be very serious.

Examples of hemoglobin in a Sentence

Recent Examples on the Web Iron supports hemoglobin production, an important protein in red blood cells that delivers oxygen to cells in the body. Casey Seiden, Parents, 26 Feb. 2024 Fossils resembling modern horseshoe crabs have been found as found back as far as 200 million years ago and their blue blood (caused by a copper-containing molecule where humans use hemoglobin) is used to test the safety of a wide variety of medicines. Andrew Wight, Forbes, 22 Feb. 2024 Oddly enough, the snow leopard doesn't have the same efficient hemoglobins as other high-altitude animals. Jack Knudson, Discover Magazine, 6 Feb. 2024 Abnormal hemoglobin alters the shape of red blood cells, turning them from discs to sickles. Emily Mullin, WIRED, 19 Dec. 2023 The switch of an A to a T in the genetic code for hemoglobin results in a hemoglobin protein with a valine instead of a glutamic acid at the sixth amino acid position. Beth Mole, Ars Technica, 8 Dec. 2023 But Hsu said modern medications are aimed at raising hemoglobin levels. Bo Erickson, CBS News, 26 Dec. 2023 For example, Tibetans living at higher altitudes have variants associated with immune resistance to new pathogens, levels of skin pigmentation, fat composition, and differences in hemoglobin levels. Laura Baisas, Popular Science, 14 Dec. 2023 Pauling showed that hemoglobin has an altered chemical structure in people with sickle cell disease. Emily Mullin, WIRED, 19 Dec. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'hemoglobin.' 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, short for earlier hematoglobulin

First Known Use

1869, in the meaning defined at sense 1

Time Traveler
The first known use of hemoglobin was in 1869

Dictionary Entries Near hemoglobin

Cite this Entry

“Hemoglobin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/hemoglobin. Accessed 2 Mar. 2024.

Kids Definition


he·​mo·​glo·​bin ˈhē-mə-ˌglō-bən How to pronounce hemoglobin (audio)
: a protein that contains iron, is the chief means of transporting oxygen in the body of vertebrate animals, occurs in the red blood cells, and is able to combine loosely with oxygen in regions (as the lungs) where it is in high concentration and release it in regions (as the tissues of the internal organs) where it is in low concentration

Medical Definition


variants or chiefly British haemoglobin
: an iron-containing respiratory pigment of vertebrate red blood cells that functions primarily in the transport of oxygen from the lungs to the tissues of the body, that consists of four polypeptide chains of which two are of the type designated alpha and two are of one of the types designated beta, gamma, or delta and each of which is linked to a heme molecule, that combines loosely and reversibly with oxygen in the lungs or gills to form oxyhemoglobin and with carbon dioxide in the tissues to form carbaminohemoglobin, that in humans is present normally in blood to the extent of 14 to 16 grams in 100 milliliters expressed sometimes on a scale of 0 to 100 with an average normal value (as 15 grams) taken as 100, and that is determined in blood either colorimetrically or by quantitative estimation of the iron present see fetal hemoglobin, hemoglobin a compare carboxyhemoglobin, methemoglobin
: any of numerous iron-containing respiratory pigments of various organisms (as invertebrates and yeasts)
hemoglobinic adjective
or chiefly British haemoglobinic
hemoglobinous adjective
or chiefly British haemoglobinous

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