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Antibody Tests (Coombs Test)

Risks

There is very little chance of a problem from having blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

Antibody tests (Coombs tests) are done to find antibodies that attack red blood cells.

Normal

No antibodies are found. This is called a negative test result.

  • Direct Coombs test. A negative test result means that your blood does not have antibodies attached to your red blood cells.
  • Indirect Coombs test. A negative test result means that your blood is compatible with the blood you are to receive by transfusion. A negative indirect Coombs test for Rh factor (Rh antibody titer) in a pregnant woman means that she has not developed antibodies against the Rh-positive blood of her baby. This means that Rh sensitization has not occurred.

Abnormal

  • Direct Coombs test. A positive result means your blood has antibodies that fight against red blood cells. This can be caused by a transfusion of incompatible blood or may be related to conditions such as hemolytic anemia or hemolytic disease of the newborn (HDN).
  • Indirect Coombs test. A positive test result means that your blood is incompatible with the donor's blood and you can't receive blood from that person. If the Rh antibody titer test is positive in a woman who is pregnant or is planning to become pregnant, it means that she has antibodies against Rh-positive blood (Rh sensitization). She will be tested early in pregnancy to check the blood type of her baby. If the baby has Rh-positive blood, the mother will be watched closely throughout the pregnancy to prevent problems to the baby's red blood cells. If sensitization has not occurred, it can be prevented by a shot of Rh immunoglobulin.

WebMD Medical Reference from Healthwise

Last Updated: March 12, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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