Clinical Definition

Rh factor blood test detects a protein, Rh factor, which can be present on the surface of erythrocytes. The majority of the population have the Rh factor and so test ”Rh positive.”  When the blood test does not detect Rh factor, the result is Rh negative. Pregnant women are tested not only for blood type (A, B, O) but also for Rh factor. Women who test Rh negative can be given Rh immunoglobulin (RhIg), made from donated blood, to prevent the production of Rh antibodies that can harm an Rh positive fetus.

In Our Own Words

Rh factor blood test is given to pregnant women to determine if they are Rh positive or negative. Rh is a protein present on the surface of the red blood cells of most people. That means they will test Rh positive. If the Rh factor is not detected, the person is Rh negative. Depending on the parents’ genes, the baby may be Rh positive or Rh negative.

A pregnant woman who is Rh negative can have problems if her fetus is Rh positive. Her body may make antibodies against the baby’s red blood cells, since they have the Rh factor on the surface. To prevent that, she can be given a shot of Rh Immunoglobulin or RhIg. This shot is made from donated blood. Once injected, it prevents the mother’s production of antibodies against Rh factor.