Rh factor testing: Difference between revisions

Revision as of 03:30, 27 March 2019

Revision as of 13:51, 8 April 2019

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[[/Rh Factor Testing]]

'''Rh factor testing''', also known as Rhesus factor testing, is the procedure of determining the rhesus D status of an individual (see Rh blood group system)<ref>{{Cite web|url=https://www.babycenter.com/0_blood-test-for-rh-status-and-antibody-screen_1480.bc|title=Blood test for Rh status and antibody screen|last=|first=|date=2019 Mar 7|website=BabyCenter|archive-url=|archive-date=|dead-url=|access-date=2019 Mar 7}}</ref>.

== Introduction ==
Rhesus factor testing utilizes the genotyping technique to detect the presence of the RhD gene. By checking the existence of RhD gene in the individual’s genome, the presence of rhesus D (RhD) antigens can be inferred. Individuals with a positive RhD status has RhD antigens expressed on the cell membrane of their red blood cells, whereas Rhesus D antigens are absent for individuals with negative RhD status.

Rhesus factor testing is usually conducted on pregnant women to determine the RhD blood group of the mother and the fetus. By confirming the RhD status of both mother and fetus, precautions can be made if necessary to prevent any medical conditions caused by rhesus incompatibility.

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=== Prevention of Rh group incompatibility in blood donation ===

When RhD antigens on red blood cells are exposed to an individual with RhD- status, high-frequency of IgG anti-RhD antibodies will be developed in the RhD- individual’s body. The antibodies then attacks red blood cells with attached RhD antigens and lead to the destruction of these cells. This condition is known as haemolytic reaction. The destruction of red blood cells releases haemoglobin to the bloodstream. Haemoglobin may be excreted through urine, causing haemoglobinuria. The sudden release of haemoglobin will also pass through the liver and be metabolized into bilirubin, which in high concentrations, accumulates under the skin to cause jaundice. Liberation of blood cell debris into the circulation will also cause disseminated intravascular coagulation and circulatory shock.

==== Symptoms of Rh group incompatibility in blood donation ====

Patients receiving incompatible blood transfusion may have pale skin, splenomegaly, hepatomegaly and the yellowing of mouth and eyes. In addition, their urine may appear in dark colour and the patients may experience dizziness and confusion. Tachycardia, the increase in heart rate, is also a symptom of the hemolytic disease.

=== Prevention of haemolytic disease of the newborn ===

In the case of pregnancy, when an RhD- mother carries an RhD+ fetus, some of the fetal red blood cells may cross the placenta into the maternal circulation, sensitizing the mother to produce anti-RhD antibodies. Since the mixing of fetal and maternal blood occurs mainly during separation of the placenta during delivery, the first RhD+ pregnancy rarely causes any danger to the fetus as delivery occurs before the synthesis of antibodies by the mother. However, if the mother were to conceive another RhD+ child in the future, the anti-RhD antibodies will cross the placenta to attack and haemolyse the red cells of the fetus, causing the aforementioned haemolytic in the fetus known as haemolytic disease of the newborn. This disease is usually fatal for the fetus and hence preventive measures are conducted.

==== Symptoms of haemolytic disease of the newborn ====

Symptoms of the disease may vary in each pregnancy. They are usually not noticeable during pregnancy. However, prenatal tests may reveal yellow colouring of amniotic fluid, which is caused by the buildup of bilirubin. Splenomegaly, cardiomegaly and hepatomegaly may occur in the baby. Excessive tissue fluid may accumulate in the stomach, lungs or scalp. These are typically signs of hydrops fetalis.

After birth, the symptoms of the child are similar to that of incompatible blood transfusion in adults.  The baby may have pale skin due to anemia. The yellowing of the umbilical cord, skin and eyes, also known as jaundice, may arise within 24 to 36 hours of birth. Signs of hydrops fetalis such as the enlargement of spleen, heart and liver, along with severe edema, will continue after birth.

=== Medical Intervention ===