Page 419 - Essential Haematology

Chapter 29 Blood transfusion / 405

detecting antibody or complement on the red cell From the p atient
surface where sensitization has occurred in vivo . Th e
1 The ABO and Rh blood group is determined.

AHG reagent is added to washed red cells and
2 Serum is screened for important antibodies by an
agglutination indicates a positive test. A positive test
indirect antiglobulin test on a large panel of anti-
occurs in haemolytic disease of the newborn,
genically typed group O red cells.
autoimmune haemolytic anaemia and haemolytic
transfusion reactions. If a red cell alloantibody is discovered in the
The indirect antiglobulin test is used to detect recipient, donor blood is selected lacking the rele-

antibodies that have coated the red cells in vitro . It vant antigen. The most likely are Rh D, C, c, E, e

is a two - stage procedure: the first step involves the and K.
incubation of test red cells with serum; in the
second step, the red cells are washed and the AHG
reagent is added. Agglutination implies that the From the d onor
original serum contained antibody which has coated
An appropriate ABO and Rh unit is selected. Donor
the red cells in vitro . This test is used as part of the

(blood) testing is described on p. 399 .
’
routine antibody screening of the recipient s serum
prior to transfusion and for detecting blood group
antibodies in a pregnant woman. The c ross - m atch

Most of the above methods were originally

developed for tube techniques. These were replaced The techniques that may be used are described in
by 96 - well microplates but most laboratories now Table 29.8 .
use gel - based technology (Fig. 29.6 ).

Electronic c ross - m atch

Cross - m atching and
In this, a patient has group and antibody screen
p re - t ransfusion t ests

performed as two separate occasions. If both are
A number of steps are taken to ensure that patients negative and no blood has been transfused between
receive compatible blood at the time of the test, ABO and Rh compatible blood is issued
transfusion. directly without wet testing.

Figure 29.6 Patient antibody

screening using the microcolumn
(gel) system: 10 tests with two
controls (tube 11 is the positive
control and tube 12 the negative
control) are shown. The patient ’ s
serum is tested against screening
cells with known red cell
phenotype. Tubes 1, 3, 5 – 8 and
10 show positive results. The
patient ’ s serum contained
a
anti - Fy . (Courtesy of Mr G.
Hazlehurst.)