What to Know About the Rh Factor

The rhesus factor, or Rh factor, is a protein that may be present on the surface of red blood cells (RBCs). If RBCs contain the Rh antigen, they are Rh-positive, and if not, they are Rh-negative. It is important to know a person’s Rh factor to ensure that they receive compatible blood.

Blood typing is a system of classifying blood based on the antigens present on or missing from the surface of RBCs. This approach to grouping bloods can prevent the severe complications that can occur from interactions between incompatible blood types.

In this article, we discuss the importance of the Rh factor and blood typing. We also explain how a person can determine their Rh status.

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The Rh factor is an inherited protein that can be present on the surface of RBCs. There are five main Rh antigens on RBCs, of which the most important is the Rh D antigen. The Rh D antigen is the most immunogenic, meaning that it may provoke an immune response.

People inherit their Rh status from their parents, separate from their ABO blood type. Although Rh status can varyTrusted Source among populations, roughly 85% of people in the United States are Rh-positive.

RBCs contain proteins, or antigens, on their surface that allow specialists to determine blood types. The absence or presence of A or B antigens and Rh factor can help classify blood types. People with no A or B antigens on the surface of their RBCs have blood type O. Combining these systems creates the eight most common blood types:

  • A-positive (A+)
  • A-negative (A-)
  • B-positive (B+)
  • B-negative (B-)
  • O-positive (O+)
  • O-negative (O-)
  • AB-positive (AB+)
  • AB-negative (AB-)

The positive or negative sign next to the ABO grouping refers to the Rh status and whether the RhD antigen is present or not. While being Rh-positive is more common, being Rh-negative does not indicate illness, and it does not usually affect a person’s health. However, it can influence their compatibility with other blood types, affecting the type of blood they can receive.

Blood typing refers to categorizing blood based on the antigens that are present on the surface of RBCs. In addition to the Rh factor, people can also use the ABO system to determine blood type. However, the 30 known blood groups comprise more than 600Trusted Source antigenic structures, meaning that some people may have rare blood types.

Determining blood types is essential for compatibility. If the immune system detects the antigens in incompatible blood, it will recognize those RBCs as foreign and destroy them, which could result in life threatening complications.

Learn more about blood types.

The Rh factor is one of the antigens that specialists use to determine blood compatibility. Checking for blood compatibility is a routine procedure during pregnancy, blood transfusions, and blood donation.

If a person experiences Rh incompatibilityTrusted Source during pregnancy — for example, if they are Rh-negative, and the baby is Rh-positive — they may produce anti-D antibodiesTrusted Source. This can cause complications with future pregnancies.

Additionally, the Rh factor is important in blood donations and transfusions. For example, an Rh-negative person can only receive Rh-negative blood. Otherwise, they may experience a hemolytic transfusion reactionTrusted Source, which can cause serious complications.

The main complication relating to Rh factors involves those who are Rh-negative encountering Rh-positive blood and producing anti-D antibodies in response. This may occur during pregnancy or if a person accidentally receives incompatible blood during a transfusion.

When a person who is Rh-negative is pregnant with an Rh-positive fetus, their body will recognize the Rh-positive blood as foreign and produce anti-D antibodies. These antibodies can cross the placenta and attack the fetus’s blood cells. Some people may refer to this as Rh disease.

Health problems do not usually occur during an Rh-negative person’s first pregnancy with an Rh-positive fetus, as the body is unlikely to produce enough anti-D antibodies. However, without treatment, later pregnancies may be at risk.

An attack by the anti-D antibodies on the fetal blood cells can result in hemolytic disease of the newborn.

When RBCs break down, they release bilirubin, which may cause jaundice. Due to a lower number of RBCs, the fetus may also experience anemia and the enlarging of their organs. In severe cases, this may result in a stillbirth.

Similarly, Rh-negative people who receive an Rh-positive blood transfusion may experienceTrusted Source an incompatible transfusion reaction, known as an acute hemolytic transfusion reaction. This reaction can produce a number of symptoms and rapidly progress to shock.

If a person is unaware of their Rh status, a healthcare provider can perform an Rh screening test. This procedure uses a blood sample to determine whether RBCs have the Rh antigen. It is also possible to perform a prenatal testTrusted Source to determine the Rh status of a fetus during pregnancy.

People may consider undergoing an Rh screening test if they plan to become pregnant, require a blood transfusion, or donate blood.

Every blood donationTrusted Source will undergo an Rh factor screening test, as well as tests for various infectious diseases, to ensure that it is safe for the recipient.

Learn more about donating blood.

The Rh factor is an antigen that some people may have on their red blood cells. Those who have this antigen are Rh-positive, while those without it are Rh-negative. Knowing a person’s Rh status is key to understanding their blood compatibility.

This compatibility is particularly important during pregnancy and when receiving a blood transfusion. In the event of incompatible blood, the body will respond by producing antibodies against the Rh antigen. These antibodies will destroy red blood cells with the Rh antigen, which can cause health complications.

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