The Coombs' test looks for antibodies that act against your red blood cells.

Blood will be taken from a vein, usually from the inside of the elbow or the back of the hand. First, the place where the needle will be inserted is cleaned with a germ-killing product (antiseptic). An elastic band (tourniquet) is placed around the upper arm to apply pressure. This causes the vein to swell with blood.

The needle is inserted into the vein, and the blood is collected into a tube. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants and young children, the area is cleansed with antiseptic and punctured with a sharp needle or object (lancet). The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to stop any bleeding.

The direct test is performed using your red blood cells and a series of pre-made antibodies. The indirect Coombs test uses the fluid that forms when blood clots (serum) and a series of standardized red blood cells.

No special preparation is necessary for this test.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing or a bruise may develop at the site where the needle was inserted.