Coombs' test, indirect

How the Test is Performed:
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 and restrict 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 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 glass 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.

How to Prepare:
Adults:
No special preparation is necessary.

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 experience, 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:



How it Feels:
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 .

Risks:

  • fainting or feeling lightheaded
  • multiple punctures to locate veins
  • excessive bleeding
  • hematoma (blood accumulating under the skin)
  • infection (a slight risk any time the skin is broken)



Why this Test is Performed:
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 (other than the major ABO system) to RBCs. This is used to determine if there will be an adverse reaction to blood that is to be used for a blood transfusion, that is, the screening portion of the "type and screen" performed for blood compatibility testing (cross-matching).

Normal Values:
No agglutination (clumping of cells) is normal.

Abnormal Results:

If there are excess antibodies (over and above what the person's red blood cells can absorb):

Additional conditions under which the test may be performed:



Cost:
The estimated cost is $25.

Special Considerations:
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.