Coombs’ test - indirect

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The indirect Coombs' test measures the presence of antibodies to red blood cells in the blood (see also Coombs' test - direct).

Indirect antiglobulin test

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. 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 or young children:

The area is cleansed with antiseptic and punctured with a sharp needle or a 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 the puncture site if there is any bleeding.

No special preparation is necessary.

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.

The indirect Coombs' test detects circulating antibodies against red blood cells (RBCs). The major use of this test is to determine if the patient has antibodies in the blood capable of attaching to RBCs. These antibodies are other than the major ABO system or the Rh type.

The test is only rarely used to diagnose a medical condition, but is essential for use by laboratories such as blood banks. Blood banks use the indirect Coombs' test to determine whether there is likely to be an adverse reaction to blood to be transfused.