What Are Blood Type and Rh Tests?

Last Editorial Review: 6/22/2017

Ask the experts

I am going to be trying to get pregnant soon, and my doctor ordered a Blood Type and Rh test; what are these tests?

Doctor's response

Blood type tests categorize your blood according to the major human blood group (ABO) system. A person's ABO type depends upon the presence or absence of two genes — the A and B genes. These genes determine part of the configuration of the red blood cell surface. Possible ABO blood groups include O, A, B, or AB.

The Rh antigen is another compound that may or may not be present on the surface of red blood cells. The Rh test determines whether this configuration is present ("Rh-positive") or absent ("Rh-negative") on an individual's blood cells.

Rh testing is performed because the difference in Rh blood group types between an Rh-negative mother and her Rh-positive baby can lead to hemolytic disease (a severe condition in which there is breakdown of the red blood cells) of the newborn. If an Rh-negative mother carries an Rh-positive fetus, she may develop antibodies against the Rh component of the baby's red blood cells. These antibodies could cause hemolytic disease of an Rh-positive baby in subsequent pregnancies. Prevention of hemolytic disease of the newborn is carried out by giving Rh-negative mothers Rh0 (D) immune globulin (brand name: RhoGAM) after delivery of an Rh-positive baby. This prevents the mother's immune system from reacting to the Rh-positive blood of any subsequent fetus.

Medically reviewed by John A. Daller, MD; American Board of Surgery with subspecialty certification in surgical critical care


"Blood donor screening: Laboratory testing"