Coombs Test - Indirect

The Indirect Coombs Test can also be used to help diagnose the cause of hemolytic anemia due to autoimmune conditions. In an autoimmune disorder, antibodies are produced against the body’s own RBCs which attack and destroy the RBCs causing hemolytic anemia. Autoimmune hemolytic anemia can be caused by autoimmune diseases like Systemic Lupus Erythematosus, mycoplasma pneumonia infections, or certain cancers like lymphocytic leukemia and lymphoma.

Both Indirect and Direct Coombs Test are performed to determine the presence of anti-human RBC antibodies directed against human RBC antigens found on the RBCs. The Indirect Coombs Test is performed to determine antibodies produced against incompatible RBCs obtained from outside the body (as during a blood transfusion or during pregnancy). Whereas, the Direct Coombs Test is performed to detect the presence of antibodies directed against the patient’s own RBCs, which occurs during autoimmune diseases. Also, antibodies detected by the Indirect Coombs Test are present in the serum, while those detected by the Direct Coombs Test are attached to the surface of the RBCs. The Direct Coombs Test is performed to confirm if hemolytic anemia is being caused due to autoimmune disorder. The Indirect Coombs Test is performed primarily to determine compatibility of blood transfusion, or to check for Rh compatibility between a pregnant woman and her child before or during pregnancy.

Hemolytic Disease of Fetus and Newborn or HDFN is a condition where the blood type of the fetus is incompatible with the blood type of the mother. The most severe reactions typically occur due to Rh incompatibility, where antibodies are produced in the Rh negative mother against Rh positive fetus. These antibodies cross the placenta and react with the RBC of the fetus, causing HDFN.