Page 368 - Concise Pathology for Exam Preparation ( PDFDrive )

12 Haematology 353

• Individuals with blood group O can receive only O blood owing to the presence of anti-
A IgM, anti-B IgM and anti-A,B IgG in their serum, which would destroy cells with A or
B antigen on their surface.
• Individuals with blood group AB (universal recipient) may receive blood from any
group, since they have no isohaemagglutinins to destroy the transfused cells.

Q. Write briefly on different blood group systems besides ABO
system.
Ans. Blood group systems besides ABO system include
1. Rh antigen system
(a) The Rh antigen system has three closely linked gene loci, coding for D antigen
(there is no d antigen), C and/or c antigen and E and/or e antigen.
(b) Thus, the antigens produced are C, D, E, c and e.
(c) An individual may have similar or different sets of these three Rh antigens on each
chromosome; for example, CDE/cde, cde/cde, or CdE/cdE (each person inherits
one trio gene from each parent).
(d) Individuals who are positive for D antigen are considered Rh-positive (85% of the
population) and those who lack it are Rh-negative.
(e) Individuals with a weak variant of D antigen, called the Du variant, are also con-
sidered Rh-positive.
(f) Alloimmunization (formation of an antibody against an antigen) occurs if a per-
son is exposed to an Rh antigen that is not on the patient’s RBCs (eg, an Rh-negative
person exposed to Rh-positive RBCs may develop anti-D antibodies).
(g) The majority of clinically important antibodies that produce a transfusion reaction
are warm-reacting (IgG) antibodies (eg, anti-D, anti-Kell) rather than cold-reacting
(IgM) antibodies.
2. Duffy antigen system: African-Americans commonly lack Duffy (Fy) antigens on
their RBCs, which protects their cells from Plasmodium vivax infestation, since P. vivax
requires Duffy antigen as a receptor to bind to the RBCs.
3. I antigen system: May be associated with cold-reacting IgM antibodies against i
antigen or I antigens leading to a cold autoimmune haemolytic anaemia (eg, anti-i
is associated with infectious mononucleosis and anti-I with Mycoplasma pneumoniae
infection).
4. Lewis antigens are closely related to ABH antigens and are produced in body secretions.
Naturally occurring IgM antibodies develop against these antigens, but they are generally
weak antibodies of no clinical importance.

Q. Write briefly on the principles of blood transfusion.
Ans. Blood transfusion involves the collection, storage and infusion of a donor’s blood to
a recipient. Routinely, ABO and Rh typing is done on donor blood, atypical antibodies,
(eg, anti-D, anti-Kell) are tested for using the indirect Coombs test, serology is done for
syphilis, hepatitis B, hepatitis C, HIV-1 and -2 and HTLV-1.

Indications for Blood Transfusion

• Traumatic haemorrhage
• Gynaecological blood loss
• Surgical blood loss
• Severe anaemias
• Coagulation disturbances
• Leukaemias
• Haemolytic anaemias
• Thalassaemia
• Peripheral circulatory failure/shock
• Burns

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