What is the Indirect Coombs test?

The Indirect Coombs test, also known as the Indirect Antiglobulin Test (IAT), is a blood test used to detect circulating antibodies that may react against red blood cells (RBCs).

Unlike the Direct Coombs test, which looks for antibodies already attached to red blood cells, the Indirect Coombs test identifies free antibodies present in the serum. These antibodies can cause destruction of red blood cells under certain conditions, such as during pregnancy or blood transfusion.

The test plays a critical role in prenatal screening, transfusion medicine, and investigation of immune-mediated anaemias.

Why do I need an Indirect Coombs test?

The Indirect Coombs test is used to identify antibodies that could cause haemolytic reactions, particularly in pregnancy or following transfusion.

You may need an Indirect Coombs test if you:

• Are pregnant or planning pregnancy
• Have Rh-negative blood type
• Are undergoing blood transfusion screening
• Have a history of transfusion reactions
• Are being investigated for immune haemolytic anaemia
• Have unexplained anaemia
• Require antibody screening before surgery

Clinical situations where this test is essential include:

• Antenatal antibody screening
• Blood group compatibility testing
• Investigation of haemolytic disease of the newborn
• Pre-transfusion safety checks

Benefits of the Indirect Coombs test

• Detects red blood cell antibodies
  Identifies antibodies that may cause haemolysis.
• Essential in pregnancy care
  Protects against haemolytic disease of the fetus and newborn.
• Improves blood transfusion safety
  Prevents transfusion reactions.
• Clinically established screening test
  Used routinely in NHS and private care.
• Supports investigation of anaemia
  Identifies immune-mediated causes.
• Guides Rh incompatibility management
  Critical for Rh-negative mothers.
• Simple blood test
  Requires only a serum sample.
• Supports early clinical intervention
  Enables timely treatment and monitoring.

Step by step – how the test works

You can access Indirect Coombs testing UK-wide through two options:

1. Clinic appointment
   Attend your nearest UK clinic, where a healthcare professional will take your blood sample.
2. At-home or hotel visit (£60 extra)
   A qualified phlebotomist comes to your home or hotel, so you don’t need to travel.

Your sample is analysed in an accredited UK laboratory, and results are delivered securely.

Your results explained

Negative Indirect Coombs test

No red blood cell antibodies detected.

Typical UK interpretation:

• Indirect Coombs: Negative

Positive Indirect Coombs test

Red blood cell antibodies detected. Further antibody identification is required.

Typical UK interpretation:

• Indirect Coombs: Positive

Clinical significance varies

Some antibodies are clinically significant, while others may not cause problems. Interpretation depends on antibody type and clinical context.