A. Direct antiglobulin test – Explanation

This patient has a haemolytic anaemia. A direct antiglobulin test is a synonym for a
direct Coombs test.

The direct Coombs test is used to test for autoimmune haemolytic anaemia or in other
words any condition of an anaemia caused by immune system lysis or destruction of red

blood cells.
Some examples of diseases that test positive for a direct Coombs test include
alloimmune haemolysis (such as Rhesus disease), autoimmune haemoloysis (such as
systemic lupus erythematosus) or drug-induced immune-mediated haemolysis.

The term “polychramasia” used in this stem refers to a disorder where there is an
abnormally high amount of immature red blood cells. A haemolytic anaemia such as
this case (or any other form of anaemia) would trigger erythropoeitin release and
increase the rate of which red blood cells are produced and released from the bone
marrow. When levels of erythropoeitin are high, immature red cells would be released
into the bloodstream.

COOMBS TEST
There are two Coombs tests:
1. The direct Coombs test (DCT, also known as direct antiglobulin test or DAT)
2. The indirect Coombs test (also known as indirect antiglobulin test or IAT)

Direct Coombs test
• Used to test for autoimmune haemolytic anaemia
•It is used to detect these antibodies or complement proteins that are bound to the
surface of red blood cells. Basically, it is used to test patients RED BLOOD
CELLS.
•A positive Coombs test indicates that an immune mechanism is attacking the
patient’s
own RBCs. Examples:
• Common examples of alloimmune haemolysis
oHaemolytic disease of the newborn (also known as HDN or erythroblastosis
fetalis)
o Rh D haemolytic disease of the newborn (also known as Rh disease)
o ABO haemolytic disease of the newborn
o Alloimmune haemolytic transfusion reactions
• Common examples of autoimmune haemolysis
o Cold agglutinin disease : Infectious mononucleosis
• Drug-induced immune-mediated hemolysis
o Penicillins, Cephalosporins

Indirect Coombs test

• Used in prenatal testing of pregnant women and in testing blood prior to a blood
transfusion.
•It detects antibodies against RBCs that are present unbound in the patient’s serum.
In this case, serum is extracted from the blood sample taken from the patient and
tested. Basically, it is used to test patients SERUM (not red blood
cells)
• If agglutination occurs, the indirect Coombs test is positive.
• Examples of use:

o Blood transfusion preparation : Antibody screening, cross matching
oAntenatal antibody screening: to screen pregnant women for IgG antibodies
that are likely to pass through the placenta into the fetal blood and cause
haemolytic disease of the newborn