A blood group and antibody test can tell you which blood group you are in. Red blood cells have certain proteins called antigens on their surface. Your plasma, the liquid part of your blood, also contains antibodies which will attack certain antigens if they are present. There are different types of red blood cell antigens - the ABO and rhesus types are the most important.
Blood group and antibody tests look for specific proteins found in your red blood cells. For a blood transfusion both donor and receiver must be compatible. The blood test can also detect if you are a carrier of sickle cell, thalassaemia or another haemoglobin disorder.
Which blood group you have depends on the blood types of your parents.
There are mainly four major blood types: A, B, AB and O.
A+ (A positive) if you have A and rhesus antigens.
A− (A negative) if you have A antigens but don't have rhesus antigens.
B+ (B positive) if you have B and rhesus antigens.
B− (B negative) if you have B antigens but don't have rhesus antigens.
AB+ (AB positive) if you have A, B and rhesus antigens.
AB− (AB negative) if you have A and B antigens but don't have rhesus antigens.
O+ (O positive) if you have neither A nor B antigens but you have rhesus antigens.
O− (O negative) if you don't have A, B or rhesus antigens.
We will need a small sample of blood to perform the test where ABO typing is evaluated. The liquid part of the blood, without cells, will also be established by using the same test sample.
If you are pregnant, blood typing can also be an important risk factor for second pregnancies. If your immune system differs from the unborn baby, who has inherited the father's genetic antibody/antigen blood group, it can result in jaundice and/or anaemia in newborns.
For all rhesus-negative mothers an indirect Coombs' test should be done at the first antenatal visit. It is important to know therefore what your blood group is. If the test is positive, antibody titres should be monitored with serial samples.
DNA obtained from maternal blood can identify pregnancies at risk of sensitisation. This is available in the UK but is not however currently universal practice.
If the Doppler scan confirms anaemia in the foetus, foetal blood sampling should be considered. It can be taken at the site of cord insertion or from the hepatic vein. This procedure is done under the guidance of ultrasound imaging. On rare occasions abortion may happen however it depends on the site of sampling and the condition of the foetus.
It is important to have plenty to drink prior to your blood test as it will be easier to draw blood.
A small amount of blood is taken using a needle inserted into a vein in your arm, near your elbow. A slight scratch or prick will be a sign that blood is being taken. The sample is then sent to a laboratory for analysis.
It is routine practice for hospitals to do blood group testing prior to an operation as a precautionary measure in cases when there is likely to be a considerable amount of blood loss. This ensures you receive the correct blood transfused if it is required.
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