Direct Coombs Test ?

Direct Coombs Test ?

Introduction

This test is performed to detect anti-D antibody or other antibodies attached to the red cell surface within the blood stream. This occurs in the following circumstances:

1. When there is a Rh-positive baby in the womb of a sensitized Rh-negative woman; the antibodies produced in mother’s serum cross the placenta and after entering the baby’s blood stream, these antibodies will attach to the baby’s Rh-positive red blood cells. These coated (or sensitized) cells are clumped and removed from the circulation, causing hemolytic anemia (hemolytic disease of the newborn: Erythroblastosis fetalis). When the baby is born, the baby’s blood is collected (or cord blood collected from umbilical cord) and tested by the antiglobulin Coomb’s test (direct) to detect anti ‘D’ antibodies coated on red blood cells.
2. Transfusion reactions
3. Drug induced red cell sensitization
4. Autoimmune hemolytic anemia.

Requirements

1. Test tube
2. Pasteur pipettes
3. Incubator
4. Centrifuge

What is Indirect Coombs Test ?

Specimen

Blood drawn into EDTA is preferred but oxalated, or clotted, citrated whole blood may be used (the specimen need not be a fasting sample).

Procedure

1. Prepare a 5% suspension in isotonic saline of the red blood cells to be tested.
2. With a clean Pasteur pipette add one drop of the prepared cell suspension to a small tube.
3. Wash three times with normal saline to remove all the traces of serum.
4. Decant completely after the last washing.
5. Add two drops of Anti-human serum.
6. Mix well and centrifuge for one minute at 1,500 RPM.
7. Resuspend the cells by gentle agitation and exámine macroscopically or microscopically for agglutination.