Blood Transfusion Practical Write Up Biology Essay

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The first step in pre-transfusion testing is the identification of blood group (ABO) of the donor and the recipient. In addition the presence of RhD antigen should also be determined to ensure that RhD negative recipients are not transfused with the RhD positive red cells (McCullough, 2005). There is 99.5% chance of getting blood compatibility if the recipient and the donor have the same ABO and RhD groups. However to make sure that the donor's red cells are 100% compatible to those of the recipient's, other antibodies that may be present in the recipient's serum should also be identified which is an important part of pre-transfusion testing (Contreras, 1998). The unknown antibodies present in the recipient's serum can be detected by serological tests in which recipient's serum is screened against the red cells panel from different donors whose antigen expression is known. The screening cells have the antigens that are able to activate the formation of clinically important antibodies such as D, C, c, E, e, K and Fya (Contreras, 1998). The main aim of the practical was to detect the presence of these clinically significant antibodies in different recipients' serum by indirect anti-globulin test (AGT), also known as Coombs test. In this test, the IgG antibodies binding to the red cells can be observed indirectly by adding the anti-human globulin (AHG) reagent (Overfield et al., 2008). If any agglutination is seen in the serum after the addition of AHG then it shows that the antibody for the particular antigen is present. The major groups tested for in the experiment were Rh (D, C, c, E and e), Kell (K) and Duffy (Fya). Indirect AGT is also used to determine the presence of weak D among the Rh- D negative individuals (Opoku-okrah et al., 2008).

Methods

The practical guide was provided and all the procedures in the guide were followed throughout the experiment (Refer to the practical guide). Serum samples from patients A, B, and C were examined against the red cells panel (1 to 5).

Results

Table 1: Table illustrating the agglutination activity of antibodies in patients' serum samples against the donors' red cell antigens

Red cells

Serum

Samples

Panel

A

B

C

D

E

F

1

-

+

-

-

+

+

2

-

+

-

-

+

+

3

-

+

-

-

+

-

4

-

+

-

-

-

+

5

-

+

-

-

-

-

6

-

-

-

-

-

-

7

-

-

-

-

-

-

8

-

-

-

-

-

-

9

-

-

-

-

-

-

10

-

-

-

-

-

-

* (+) indicates the positive result for agglutination and (-) indicates the negative result for agglutination.

The results for the remaining serum samples against the red cell antigens were acquired from the other group members. Table 1 demonstrates all the results obtained from all the group members. From the above table, it can be seen that no agglutination activity was observed in the serum samples of patients A, C and D. This suggests that there were no antibodies present in the serum of patients A, C, and D against the antigens shown in the panel provided. In contrast antibodies in serum sample B showed agglutination activity against 1, 2, 3, 4, and 5 red cells panel. Using the panel provided, it was found that serum from patient D contained anti-C, anti-D, and anti-E antibodies. Similarly, there was agglutination in serum sample of patient E against red cells 1, 2, and 3 showing the presence of anti-D antibody in the serum. In addition, serum sample in patient F showed agglutination against 1, 2, and 4 red cells. The serum in the recipient F was found to have anti-C antibodies.

Discussion

From the different pattern of agglutination reactions against different antigens, the antibodies present in the patient's serum can be identified. The results showed the presence of clinically significant antibodies in patients B, E and F. The presence of these antibodies against Rh system suggests that these patients are Rh negative as they are producing alloantibody against the donor's red cells. It also tells that the blood of patients B, E and F is not compatible to the donor's. In contrast the serum sample of patients A, C and D did not show any agglutination suggesting that they are not producing any antibodies against the donor's red cells antigens. Hence this suggests that blood of patients A, C and D is compatible to the donor's blood.

Patients D and E do not have any Rh D antigens on their red cell surface and hence they are Rh D negative. Therefore it is very important to ensure that the patients E and F are transfused with Rh D negative red cells. If they are transfused with Rh D positive red cells then antibodies would be produced causing destruction of the red cells (Ravel, 1995). Moreover, if the patients E and F are pregnant women carrying Rh D positive foetus then there is a high risk of getting Haemolytic Disease of Newborn (HDN). This is because the mother's immune system identifies the foetus's blood as "foreign" producing IgM anti-D antibodies that can cross the placenta and hence destroying baby's red cells (Opoku-okrah et al., 2008).

The most common cause of severe HDN is the presence of anti-D antibody; however other clinically significant antibodies such as anti-K and anti-c are also responsible in causing different degrees of haemolytic disease in the newborn. Anti-c causes milder disease compared to RhD HDN whereas presence of anti-K antibody is less significant in causing HDN (Contreras, 1998). Other antibodies except anti-D, anti-K and anti-c antibodies are not likely to cause fetal haemolytic disease even though the treatment may be required to the newborn. In particular pregnant women should be screened for antibody to determine HDN and see the severity of the disease because anti-D being IgM can easily cross the placenta (Contreras, 1998). Rh D negative mothers are given prophylactic anti-D immunoglobulin that destroys baby's blood before mother produces antibodies. Hence mother cannot produce antibodies responsible for causing HDN in her future pregnancies (Urbaniak and Greiss, 2000).

The Rh grouping is the most immunogenic system and among all, RhD is the most significant and normally detected easily; however due to variation in expression there may be presence of weak antigens (Kumar et al., 2005). Some individuals have D antigen in their red cells that react weakly or may not even react with anti-D reagents and hence may show to have Rh D negative. They are called weak D and can only be detected by specific indirect AGT (Contreras, 1998). Weak D may arise because of weakening of D antigen, or RhD gene encoding weak antigen or may also be due to lack of a part of the D antigen (Kumar et al., 2005).

It is more important to test for the weak D antigen with donors because if the weak D red cells are given to the Rh D negative recipient then the recipient's serum produces anti- D antibodies resulting in alloimmunisation to the Rh D antigen (Kumar et al., 2005). This causes the destruction of red cells from the donor and therefore weak D donors are normally considered as Rh D positive (Ravel, 1995). In contrast if a weak D recipient is screened as Rh D negative and is given Rh D negative blood then there is no any harm to the recipient. Therefore indirect agglutination is not required to detect whether a recipient is weak D or not (Klein and Anstee, 2005).

The anti-globulin test is the most useful test that detects the clinically important antibodies that is why the risk of getting false negative results should be reduced. If the red cells are not washed properly before adding anti-human globulin (AHG) then the serum globulin may still be present. This causes neutralisation of the AHG which leads to false negative result. The poor technique performed while reading the results may disrupt the agglutinates which may cause to obtain false negative result (Overfield et al., 2008). Rh typing is generally done by agglutination, however sometimes this technique may not determine the accurate typing for instance in patients with autoimmune haemolytic anaemia. Hence in such cases, multiplex PCR can be performed to determine the correct Rh D type (Cotorruelo et al., 2000).

It can be concluded that Rh blood grouping is very important part of pre- transfusion process after ABO blood grouping. Rh D, the most antigenic antigen, has a great role in transfusion incompatibility and pregnancy. In addition indirect AGT plays a major role in pre-transfusion because it determines whether an individual is weak D or not. It is very important to screen for weak D as well as for weak c and weak E.

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