Coombs test

The direct Coombs test detects antibodies that are stuck to the surface of the red blood cells.

The direct Coombs test is used to detect antibodies or complement proteins attached to the surface of red blood cells.

[4] Coombs tests are performed using RBCs or serum (direct or indirect, respectively) from venous whole blood samples which are taken from patients by venipuncture.

The clinical significance of the result is assessed by the physician who requested the Coombs test, perhaps with assistance from a laboratory-based hematologist.

The direct Coombs test is used clinically when immune-mediated hemolytic anemia (antibody-mediated destruction of RBCs) is suspected.

If immunoglobulin or complement factors have been fixed on to the RBC surface in-vitro, the antihuman globulin will agglutinate the RBCs and the direct Coombs test will be positive.

(A visual representation of a positive direct Coombs test is shown in the upper half of the schematic).

In antenatal care, the IAT is used to screen pregnant women for antibodies that may cause hemolytic disease of the newborn.

The indirect Coombs test is used 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.

(A cross match is shown visually in the lower half of the schematic as an example of an indirect Coombs test).

[citation needed] Nonpatient, washed red blood cells (RBCs) with known antigens are incubated with patient serum containing unknown antibody content.

[citation needed] The RBCs are washed three or four times with isotonic saline solution and then incubated with antihuman globulin.

Common potentiators include low ionic strength solution (LISS), albumin, polyethylene glycol (PEG), and proteolytic enzymes.