Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure, which restricts blood flow through the vein. This causes veins below the tourniquet to distend (fill 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 tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed and the puncture site is covered with gauze or with a bandage to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Adults:
No special preparation is necessary for this test.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

• Infant test/procedure preparation (birth to 1 year)
• Toddler test/procedure preparation (1 to 3 years)
• Preschooler test/procedure preparation (3 to 6 years)
• Schoolage test/procedure preparation (6 to 12 years)
• Adolescent test/procedure preparation (12 to 18 years)

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 direct Coombs' test is used to detect autoantibodies against your own red blood cells (RBCs). Many diseases and drugs (e.g., quinidine, methyldopa, and procainamide) can lead to production of these antibodies.

These antibodies sometimes destroy red blood cells and cause anemia. This test is sometimes performed to diagnose the cause of anemia, jaundice, or abnormalities in the appearance of red blood cells under the microscope.

No agglutination (i.e., the absence of clumping of cells) is normal.

A positive direct Coombs' test indicates antibodies against the red blood cells, which may indicate one of the following conditions:

• Autoimmune hemolytic anemia without another underlying cause
• Drug-induced hemolytic anemia (many drugs have been associated with this complication)
• Erythroblastosis fetalis (hemolytic disease of the newborn
• Infectious mononucleosis
• Mycoplasmal infection
• Syphilis
• Chronic lymphocytic leukemia or other lymphoproliferative disorder
• Systemic lupus erythematosus or another rheumatologic condition
• Transfusion reaction, such as one due to improperly matched units of blood

The test is also abnormal in some people without any clear cause, especially among the elderly. Up to 3% of people who are in the hospital without a known blood disorder will have an abnormal direct Coombs' test.

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins