Rh positive

or Rh-pos·i·tive

[ ahr-eych poz-i-tiv ]
/ ˈɑrˈeɪtʃ ˈpɒz ɪ tɪv /


See under Rh factor.

Origin of Rh positive

First recorded in 1955–60

Rh factor

[ ahr-eych fak-ter ]
/ ˈɑrˈeɪtʃ ˌfæk tər /

noun Physiology.

any of a type of specific antigen present on the surface of red blood cells, persons having inherited such antigens being designated Rh+ (Rh positive) and persons lacking them, a much smaller group, being designated Rh− (Rh negative): blood of Rh− persons is incompatible with Rh+ blood because of antibody reaction, and an Rh− woman who bears an Rh+ baby will have formed antibodies to the fetal blood that, unless removed from her bloodstream by apheresis in a subsequent pregnancy, will be carried across the placenta and destroy red blood cells of the next Rh+ fetus, resulting in erythroblastosis in the newborn.

Origin of Rh factor

First recorded in 1940–45; so called because first found in the blood of rhesus monkeys

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for rh-positive

Rh positive


blood containing the Rh factor
a person having such blood

Rh factor


an agglutinogen commonly found in human blood: it may cause a haemolytic reaction, esp during pregnancy or following transfusion of blood that does not contain this agglutinogenFull name: rhesus factor See also Rh positive, Rh negative

Word Origin for Rh factor

C20: named after the rhesus monkey, in which it was first discovered

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for rh-positive

Rh factor

1942, from the first letters of rhesus; so called because the blood group, and its effects, were discovered in the blood of rhesus monkeys (1941).

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for rh-positive



Containing an Rh factor.

Rh factor


Any of several substances on the surface of red blood cells that induce a strong antigenic response in individuals lacking the substance.

The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Science definitions for rh-positive

Rh factor

[ ärāch ]

Any of several antigens present on the surface of red blood cells in most humans. People with Rh factors are classified as having a blood type that is Rh positive, while people who lack the antigen are said to be Rh negative and can produce powerful antibodies that destroy red blood cells if given a blood transfusion from an Rh-positive donor. A woman who is Rh negative and is pregnant with an Rh-positive fetus can produce antibodies that are life threatening to the fetus. See Note at blood type.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Culture definitions for rh-positive

Rh factor

[ (ahr-aych) ]

Any of several substances found on the surface of red blood cells in persons.


An Rh-negative woman who gives birth to an Rh-positive baby may develop antibodies to the Rh factor during her first pregnancy. These antibodies may cause a disorder in Rh-positive babies conceived afterward that could result in the death of the infant if the condition is not recognized and treated.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.