The indirect Coombs' test is done on a sample of the liquid part of the blood. It detects antibodies that are present in the bloodstream and could bind to certain red blood cells and destroy them. A Coombs' test involves taking a sample of blood.
It is placed in the middle of the chest or thoracic cavity (middle mediastinum), posterior to the body of sternum and the second to sixth costal cartilages and anterior to the fifth to the eighth thoracic vertebrae.
Answer Wiki. The heart, actually, is located in the center of the chest, behind the sternum (or the breastbone). However, a part of it is slightly offset to the left, as you can figure out from the picture above. For understanding this, I think prerequisite knowledge of the heart's basic anatomy is required.