Rh Blood Group

Dr Babina Thangjam *

Each person's blood is one of the four major types: A, B, AB, or O. This is the ABO system of blood typing/grouping. Blood types are determined by the type of antigens on the blood cells. Antigens are proteins on the surface of blood cells that can cause a response from the body's immune system.

The Rh factor is a type of protein on the surface of red blood cells. Most people who have the Rh factor are Rh-positive. Those who do not have the Rh factor are Rh-negative.

After the ABO system, the Rh (Rhesus) blood group system is the second most important blood group system, as some of the severe haemolytic transfusion reactions and most haemolytic disease of the foetus and newborn (HDFN) cases are associated with antibodies to the Rh group antigens.

WHAT IS Rh TYPING TEST?

Rh typing is used to determine whether a person has the specific protein, "Rh factor" on the outer layer of the red blood cells (RBCs). If a person does not have Rh factor in the blood, he or she is Rh-negative. If one has Rh factor in the blood, he or she is Rh-positive. Most people are Rh positive, but

Rh-negative blood types can be passed down from parents to children.

Rh typing is important during pregnancy. If the mother is Rh-negative and the baby is Rh-positive, it is possible that there can be Rh incompatibility. During pregnancy, it is possible that some of the baby's blood could pass through the placenta into the mother's body.

The mother's body may react to the baby's blood as a foreign substance and produce antibodies against it. This can cause a miscarriage, anaemia, and problems in later pregnancies. The first pregnancy is usually not affected by Rh incompatibility because the baby is often born before the antibodies develop. These risks can be lowered by a shot or shots of Rh immunoglobulin during each subsequent pregnancy.

WHY IS THE TEST NEEDED?

Pregnant women typically has this test at their first prenatal appointment. A person may need this test under the following conditions:

o Pregnancy.

o Thinking about becoming pregnant.

o The father of an unborn baby.

o Rh-negative and having a baby with a man who is Rh-positive.

o In need of blood transfusion.

o Donating blood.

Rh NEGATIVE IN A PREGNANT WOMAN

If a woman is Rh-negative, she may develop antibodies to an Rh-positive baby. If a small amount of the baby's blood mixes with the mother's blood, which often happens, the mother's body may react as if it were allergic to the baby and may produce antibodies to the Rh antigens. This means the mother has become sensitised and her antibodies can cross the placenta and attack her baby's blood.

They may break down the foetus's red blood cells and produce anaemia (low number of red blood cells). This condition is called haemolytic disease or haemolytic anaemia. It can become severe enough to cause serious illness, brain damage, or even death in the foetus or newborn.

OTHER TESTS THAT MIGHT BE DONE ALONG WITH IT

If a woman has a Rh typing test and the result shows that she is Rh negative, she may need to have another test called an antibody screen (Indirect Coomb's Test). The antibody screen looks for antibodies in her blood. This means she has been exposed to Rh-positive blood and developed antibodies to it. She may need multiple antibody screens during her pregnancy and one at the time of delivery.

After the delivery, the baby's blood (cord blood) is also tested for the presence of antibodies on the red blood cells (Direct Coomb's Test)

PREPARATION FOR THE TEST

There are no special preparations required for this test. However, it is important to tell the health care provider detailed information.

WHAT DO THE RESULTS MEAN?

Having Rh factor in the blood means the person is Rh-positive. If one does not have Rh factor, it means he/she is Rh-negative. If a woman is Rh-negative and is having a baby with a man who is Rh-positive, she as well as the baby could be at risk during pregnancy and post-delivery.

WHAT MIGHT AFFECT THE TEST RESULTS?

Nothing is likely to affect the test results. This includes diet, lifestyle, and medications.