Positive Coombs test: what to do and what it means

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Positive Coombs test

The Coombs test is performed on the baby's blood sample, usually for jaundice when hemolytic anemia is suspected. The research exam antibodies directed against red blood cells (RBC) which can cause autoimmune hemolytic anemia. The examination can be direct or indirect, let's see what the difference is, when it should be done and what happens if the Coombs test is positive.

In this article

  • What is the Coombs test
  • Positive coombs test in the newborn
  • Positive indirect Coombs test in pregnancy
  • To do
  • Positive coombs test and immunoprophylaxis

What is the Coombs test

There are two types of Coombs test: direct and indirect.

  • Il direct test searches for antibodies that attack red blood cells and is useful for diagnosing diseases such as infectious mononucleosis, systemic lupus erythematosus (SLE), rheumatoid arthritis, scleroderma, tuberculosis, hemolytic disease of the newborn (BUT).
  • Il indirect test tests for antibodies circulating in the blood and directed against red blood cells, is performed in pregnancy to evaluate any incompatibility of the blood group and Rh factor between mother and child and to search for the presence of free anti-Rh antibodies in the mother's blood that could cross the placenta and attack the fetus's red blood cells, but it is also done before a transfusion to assess blood compatibility.

Positive coombs test in the newborn

The two most commonly known forms of antibody-mediated hemolytic anemia in newborns are Rh incompatibility and ABO incompatibility.

  1. L'Rh incompatibility occurs when a mother has a Rh negative blood type and gives birth to a baby who is Rh positive. If maternal and fetal blood mix during pregnancy or delivery, then the mother's Rh antibodies will vigorously attack the baby's Rh +.
  2. LABO incompatibility occurs with more or less the same mechanism: mothers who have blood type 0 carry both anti-A and anti-B antibodies, if the newborn has a blood group of type A, B or AB there may be incompatibility and antibodies they can attack the baby's red blood cells causing hemolysis.

Positive indirect Coombs test in pregnancy

Un positive indirect Coombs test in pregnancy requires an immediate assessment of the antibody situation in order to understand the risk of the neonate developing fetal haemolytic syndrome and fetal anemia.

Read also: Rh factor incompatibility

To do

The main reason a person can turn out positive on the Coombs test is that she was exposed to red blood cells not her own, for example after the pregnancy or with one transfusion.

It is good to know that a positive Coombs test it does not necessarily involve hyperbilirubinemia in the newborn: the risk that the newborn needs phototherapy is certainly greater, but there are several factors that influence the bilirubin levels and the doctor will evaluate the overall picture.

At the time of childbirth the Indirect Coombs test (search for irregular anti erythrocyte antibodies) and then ABO / Rh typing and direct antiglobulin test (direct Coombs test, TAD).

At the same time also with a Coombs test negative there may be active hemolysis, possibly due to a hereditary condition or genetic deficiency. These are conditions that do not involve RBCs and therefore the Coombs test will be negative.

Positive coombs test and immunoprophylaxis

The most frequent case concerns the Rh factor: the blood group of the mother is Rh negative, that of the father Rh positive and the fetus is Rh positive. The mother's body can develop antibodies that attack the red blood cells of the newborn. Generally this does not happen during the first pregnancy but in the second one since in most cases the maternal organism develops antibodies after delivery.

In this case, we intervene with an immunoprophylaxis in the intramuscular administration of human anti-D immunoglobulins in women with Rh factor negative, this prevents the formation of maternal antibodies against the baby's red blood cells.


  • Stanford University
  • Coombs test

  • fetal anemia
  • neonatal anemia
  • rh factor
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