Coombs test or antiglobulin test (AGT) is a blood test used in immunohematology to detect antibodies against red blood cells (erythrocytes) in the blood. Blood samples can be taken during delivery from the baby’s umbilical cord or the veins after birth.
Read this post to learn more about the different types and interpretations of coombs test results and outcomes for babies with positive Coombs tests.
Types Of Coombs Tests
There are two types of Coombs tests to detect various pathologies (1).
1. Direct Coombs test
Direct Coombs test detects antibodies attached to the red blood cells. After collecting the blood sample, the red blood cells are washed in the laboratory to remove the plasma and unbound antibodies. The washed red blood cells are incubated with Coombs reagent (anti-human globulin) in the next step.
The test is considered positive if the red blood cells agglutinate, that is, appear clumpy or sticky. This indicates that the antibodies or complement proteins are attached to the red blood cells causing their destruction. A baby with a positive direct Coombs test may have autoimmune hemolytic anemia.
2. Indirect Coombs test
Indirect Coombs test detects free antibodies in the blood. These antibodies are not attached to the red blood cells and work against foreign red blood cells. In the laboratory, the blood serum is extracted and incubated with foreign red blood cells and anti-human globulin or Coombs reagent. Indirect Coombs test is considered positive if agglutination is observed.
Indirect Coombs tests help diagnose reactions to blood transfusion. It is also used in prenatal testing to check for Rh compatibility issues in pregnant women. Mothers with Rh-negative blood groups should take an Rh immunoglobulin shot during pregnancy to avoid Rh incompatibility-related complications in their subsequent pregnancies (2).
What Problems Are Seen In Coombs Positive Babies?
The health problems in positive direct and indirect Coombs tests may vary. These may include (3):
1. Autoimmune hemolytic anemia
In this condition, the immune system destroys the red blood cells, resulting in anemia. The lifespan of red blood cells is 120 days, but they are destroyed earlier in this condition. It could lead to anemia since there are inadequate mature cells to compensate for the loss.
Swelling under the skin is one of the common symptoms of hemolytic anemia in babies. Destruction of red blood cells could also cause jaundice.
Yellow discoloration of skin and whites of the eyes (sclera) is called jaundice. It is caused by excess bilirubin, a byproduct of red blood cell destruction. Babies with indirect or direct Coombs positive test could have jaundice since both attached and free antibodies damage the red blood cells.
Note: Coombs negative babies may also develop jaundice due to immature liver function, breast milk, or erythrocyte disorders.
How To Take Care Of A Coombs Positive Baby?
There is no need for specific treatment in some babies with mild elevation of bilirubin levels. However, babies are closely monitored for changes in bilirubin levels and symptoms. Treatment options may include the following.
- Adequate feeding is recommended since poor feeding may worsen jaundice due to other reasons
- Intravenous fluids are given if required
- Medications to keep blood pressure normal
- Phototherapy is given for jaundice
- Severe cases may require a blood transfusion
You may discuss the appropriate treatment plan with a pediatrician.
When Can A Coombs Positive Newborn Go Home?
Coombs positive babies can go home in usual time after birth unless there are complications of high bilirubin levels and anemia. However, you may need to visit a pediatrician within a few days for blood tests to assess the progress.
Sometimes, jaundice and anemia may worsen after going home. You may call the healthcare provider if you notice any of these signs and symptoms (4).
- Increased yellowing of the skin and eye
- Poor feeding
- Breathing difficulties or fast breathing
Long-term Complications In Coombs Positive Infants
Most Coombs positive babies do not develop any long-term problems since the maternal antibodies clear within a few weeks after birth. The immune reaction slowly resolves, and the formation of new blood cells helps the infant recover completely in a few weeks (4).
If left untreated, very high bilirubin levels may cause brain damage known as kernicterus and other issues, such as cerebral palsy or deafness. However, in most cases, jaundice is diagnosed and treated before the bilirubin reaches a level high enough to cause complications.
What Happens If The Coombs Test Is Negative?
A negative result (no agglutination present) on direct and indirect Coombs tests means no antibodies or complement proteins are against the red blood cells. It is possible to develop jaundice and hemolytic anemia in babies with negative Coombs tests due to other medical conditions that do not involve antibodies against the red blood cells. Newborns may also develop physiological jaundice and breast milk jaundice during the initial days of life (5).
Coombs test helps detect antibodies against red blood cells and determine any related underlying issues. If you are an Rh-negative mother, you may consider testing and taking Rh immunoglobulin injections to avoid complications. Severe cases can also be treated with intrauterine blood transfusions. If the baby has a positive Coombs test, they may require close monitoring, and their health condition will eventually improve over time.
2. The Rh Factor: How It Can Affect Your Pregnancy; American College of Obstetricians and Gynecologists
3. Coombs Antibody Test (Indirect and Direct); Michigan Medicine; University of Michigan
4. Direct Coombs Test (DCT);; National Health Service
5. The Coombs Test; Stanford Medicine