The Indirect Coombs' Test is a serological test to detect and identify antibodies against red blood cell (RBC) antigens in a patient's serum. It is commonly employed in the following scenarios:

Pre-transfusion Testing: To screen for unexpected antibodies in a patient's serum that might react with donor RBCs, helping to ensure compatibility between donor and recipient.

Pregnancy: To detect antibodies in a pregnant woman's blood that might target the fetus's RBCs, particularly in Rh incompatibility.

Diagnosis of Hemolytic Disease: To assist in diagnosing autoimmune hemolytic anaemia or drug-induced hemolytic anaemia.

Interpretation:

A positive result may require further investigation to identify the specific antibody or antibodies present and to determine the clinical significance.

A negative result typically indicates that the patient does not have the antibodies being tested for, although false negatives can occur in certain situations.

Note: The Indirect Coombs' Test is a sensitive and specific method, but results must be interpreted in the context of the patient's clinical situation and history. It is distinct from the Direct Coombs' Test, which is used to detect antibodies or complement proteins attached directly to a patient's own RBCs.