Thalassaemia (tests)

Thalassaemia (red cell osmotic fragility, haemoglobin electrophoresis) and indirect Coombs test
The tests used to diagnose a disease called thalassaemia and the indirect Coombs test are recommended by the doctor during pregnancy (or, in the case of the first, also when a couple is planning to have a baby). Both aim to make future parents aware of any risks that could affect the baby.
Why they are done
The tests used to diagnose thalassaemia (in addition to the routine full blood count, which is the test that first raises the doctor’s suspicion) are:

The red cell osmotic fragility test
Haemoglobin electrophoresis.

These tests are recommended before or during pregnancy so that future parents, especially if both are “thalassaemia carriers”, are prepared for the possibility of having a child with this disorder. Thalassaemia, also called Mediterranean anaemia, is a congenital disorder of the red blood cells, i.e. present from birth, that is inherited. In practice, the red blood cells of “thalassaemia carriers” contain less haemoglobin than normal (haemoglobin is the protein inside red blood cells that carries oxygen to the tissues to keep them alive). If thalassaemia is inherited from both parents (i.e. both are carriers), it is called thalassaemia major, which is fortunately quite rare (the person then needs continuous transfusions and treatment). It is less rare for thalassaemia to be inherited from only one parent (i.e. only one is a carrier), and this is called thalassaemia minor. This is not a true disease but rather a condition in which the person makes red blood cells lacking in haemoglobin. There are therefore many red blood cells (above normal) and little haemoglobin (below normal), and the red blood cells, which are normally of a certain size, are much smaller (this is already visible in the full blood count, in which they are examined under the microscope).

The indirect Coombs test, on the other hand, is essential in pregnant women if the mother’s blood is Rh- (negative) and the father’s blood is Rh+ (positive). If the baby is Rh+ (positive), some of the baby’s red blood cells can pass to the mother through the placenta, and the woman’s body may then produce antibodies against the baby’s blood (which it regards as foreign and therefore to be fought). The problem arises not so much in the first pregnancy, when the woman’s defences are weak, but in the following one if the baby is again Rh+ (positive), because the mother’s antibodies are already present and, when the baby’s red blood cells pass into the woman through the placenta, the body’s defences react. The mother’s antibodies can in turn pass to the baby through the placenta and damage the baby’s red blood cells, causing severe anaemia. For this reason, today, once a first baby with Rh+ (positive) blood has been born, the mother is given prophylaxis within seventy-two hours of the birth, i.e. an injection to inactivate any antibodies, so that any second pregnancy with an Rh+ (positive) baby can proceed safely. There is no problem if both parents are Rh- (negative), or if the mother is Rh+ (positive) and the father Rh- (negative), or if the baby is Rh- (negative), because no antibody production is triggered.