The Coombs' test detects antibodies, or proteins that react against other molecules.
A person about to undergo a blood transfusion should have this test done.
A blood sample is taken from a vein on the forearm or hand. To take a blood sample, the skin over the vein is cleaned with an antiseptic and a strong rubber tube, or "tourniquet," is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle and is collected in a syringe or vial for testing in the laboratory. After the needle is taken out of the vein, the puncture site is covered with a bandaid for a short time to prevent bleeding. When the sample is taken to the laboratory, a simple test is performed to see if the red blood cells clump together.
Individuals who are scheduled to have the Coombs' test should request specific instructions from a healthcare professional.
Normally, red blood cells do not clump together. If clumping does occur as seen on the Coombs' test, it may mean that the blood of the donor is incompatible with the serum of the potential recipient.