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Indirect Coombs Test with Titration

120 Azn
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The Indirect Coombs Test is used to detect antibodies in the bloodstream that are formed against red blood cells. These antibodies may develop due to exposure to foreign red blood cells during a blood transfusion or pregnancy.

Normal Presence of Antigens on Red Blood Cells

  • Red blood cells naturally carry specific antigens on their surface, determined by maternal and paternal genetics.
  • Two primary antigens in the ABO blood group system are A and B. Blood is categorized based on the presence or absence of these antigens.
  • Another important antigen, D, determines the Rh factor:
    • Rh-positive: D antigen is present on red blood cells.
    • Rh-negative: D antigen is absent.
  • In addition to these, there are many other red blood cell antigens, such as the Kell, Lewis, and Kidd blood group systems.

Reasons for Developing Antibodies Against Red Blood Cells

  1. After a Blood Transfusion:

    • ABO and Rh Antibodies: These are naturally formed without prior exposure to foreign antigens. Blood type and Rh factor compatibility are checked before transfusion to avoid severe transfusion reactions.
    • Other Blood Group Antibodies: Antigens like Kell or Kidd can trigger antibody formation after exposure during transfusion.
    • Recipients of multiple blood transfusions are at a higher risk of developing antibodies due to exposure to a wider variety of red blood cell antigens.

  2. Mother-Child Blood Group Incompatibility:

    • Antigens absent in the mother’s red blood cells may be inherited by the child from the father.
    • During pregnancy or delivery, fetal red blood cells may enter the maternal bloodstream through the placenta.
    • The maternal immune system recognizes these antigens as foreign and produces antibodies against them.
    • This phenomenon usually does not affect the first pregnancy but may occur in subsequent pregnancies.
    • Maternal antibodies can cross the placenta, attach to the fetal red blood cells, and cause hemolytic disease of the fetus/newborn (HDFN) by destroying the fetal red blood cells.
    • The Indirect Coombs Test detects whether the mother has produced antibodies against fetal red blood cells.

How Antibodies Develop:

  • Antibodies are initially produced during the first exposure to foreign red blood cell antigens (e.g., during a transfusion or pregnancy).
  • During this initial exposure, the immune system may not produce enough antibodies to destroy foreign red blood cells.
  • In subsequent exposures (e.g., another transfusion or a subsequent pregnancy), the immune system is primed and produces a sufficient quantity of antibodies, which can bind to and destroy the transfused or fetal red blood cells, leading to hemolysis.

 

 

  • The test is performed on a blood sample taken from a vein.
  • A 12–14 hour fast is required before the test.
  • Avoid psycho-emotional and physical stress, as well as alcohol consumption, prior to the test.

The Indirect Coombs Test is primarily used to detect antibodies against the Rh factor.

  1. Maternal-Fetal Rh Incompatibility:

    • In cases where an Rh-negative mother and Rh-positive father have an Rh-positive baby, fetal red blood cells may enter the maternal bloodstream during pregnancy or delivery.
    • The mother’s immune system produces anti-Rh antibodies in response to the foreign Rh+ red blood cells, which can pose a risk to future pregnancies.
    • Every woman should undergo Rh factor testing before or during pregnancy to determine if she is Rh-negative.
    • Rh-negative women should also check for antibodies against Rh-positive red blood cells using this test.

  2. For Administering Immunoglobulin Injections:

    • To assess the likelihood of fetal red blood cells entering the blood of an Rh-negative pregnant woman in cases such as:
      • Pregnancy, ectopic pregnancy, induced labor, or miscarriage.
      • Amniotic sac perforation or abdominal trauma.
      • Artificial interventions affecting fetal condition.

  3. Postpartum Assessment:

    • To determine if an Rh-negative woman who gave birth to an Rh-positive baby and received immunoglobulin injections has developed antibodies against Rh-positive red blood cells.

  1. Positive Result:

    • Indicates the presence of antibodies, suggesting a risk of Rh incompatibility or Rh conflict.

  2. Negative Result:

    • No antibodies detected, indicating a low likelihood of Rh conflict.

This test is crucial for preventing complications such as hemolytic disease of the newborn (HDN) and for managing Rh-negative pregnancies effectively.