What Does It Mean to Be Coombs Positive?

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It's a thrilling moment to welcome your baby into the world. Your healthcare team will be by your side, celebrating with you and ensuring your newborn is well. You may be used to hearing about Apgar scores once your infant arrives, but other tests are done as well, including one to see if your baby is Coombs positive.

A Coombs-positive diagnosis is usually not serious but does require that your baby receive medical monitoring. Let's take a closer look to understand what it means to be Coombs positive, what causes the condition, and how it's treated.

What Does a Coombs-Positive Diagnosis Mean?

When a baby is Coombs positive, their blood and their mother’s blood are different types and have mixed during pregnancy and/or delivery. It is determined by a Coombs test or direct antibody test (DAT), usually done on blood from the baby’s umbilical cord.

This combination of blood types can become a problem for the baby, causing jaundice and anemia, conditions that require extra care. While most Coombs-positive babies go home from the hospital at the usual time, they need additional evaluation by medical professionals and possibly treatment, such as phototherapy (exposing the baby to a special kind of light).  

What Causes a Baby to Be Coombs Positive?

A Coombs-positive test result occurs due to a reaction in the newborn's bloodstream. It's not uncommon for babies to have a different blood type than their mother. During pregnancy and birth, the mother’s and baby’s blood can mix. When the mother’s and baby’s blood group or type are different and not compatible, the mother’s immune system may recognize the baby’s red blood cells as foreign and produce antibodies.

"These antibodies can cross over to the baby during pregnancy and birth and damage the baby’s red blood cells," explains Athis Arunachalam, MD, assistant professor of pediatrics at Baylor College of Medicine. W"hen the baby’s red blood cells are damaged and broken down, bilirubin (a yellow pigment) is produced in excessive amounts. That's called jaundice and needs to be treated if severe."

Symptoms of Coombs-Positive Babies

When a baby is Coombs positive, their blood cells break down at a higher-than-usual rate due to the interaction of the two different blood types. This can cause jaundice and also anemia.

Jaundice

Jaundice causes the skin and whites of the eyes to appear yellow. This is a sign of too much bilirubin (the orange-yellow pigment that occurs as red blood cells break down) in the bloodstream. It gets deposited under the skin and is responsible for the yellow tone.

Many newborns develop mild jaundice. It usually gets better or goes away on its own. Coombs-positive babies are at higher risk for jaundice, though, and this can become a serious issue if it’s a severe, untreated case. As a result, vigilance is important.

Anemia

Anemic babies have a deficiency of red blood cells, which carry oxygen. Newborns with anemia can be pale, feed poorly, be very sleepy to the point of lethargy, and have increased breathing and heart rates. While most Coombs-positive babies do not become anemic, it is an elevated risk of this condition. 

Diagnosing Coombs-Positive Babies

This condition is diagnosed by a blood test that you may hear referred to as either a Coombs test or direct antibody test (DAT). "A Coombs test is routinely done on [newborns] who have different blood types than their mother’s," says Dr. Arunachalam. "A positive test means that the baby’s red blood cells have the mother’s antibodies attached to them, putting them at high risk of developing moderate to severe jaundice after birth."

Usually, the blood is taken from the baby’s umbilical cord while it is still attached to the placenta following delivery, explains Kelly L. Ross, MD, Associate Professor, Washington University School of Medicine, St. Louis Children's Hospital. Sometimes it is taken directly from the baby.

It's worth noting that a Coombs test can yield a false-positive result, typically when a pregnant person has been treated for having Rh-negative blood during a routine prenatal screening, says Dr. Ross. If their blood is Rh negative (Rh-), they may receive an injection known as Rho(D) immune globulin during pregnancy. This shot is designed to prevent them from making antibodies against their baby’s blood. This protective procedure can in some cases cause the results of a Coombs test to be positive for a baby.

"Newborns who are Coombs positive for this reason do not develop either jaundice or anemia," says Dr. Ross. Your medical records will reflect whether you have had this treatment. If your baby tests as Coombs positive, your healthcare providers will know that this prenatal shot is responsible for the test result.

Treatment for Coombs-Positive Babies

When your baby is diagnosed as Coombs positive, they will need a bit of extra monitoring to ensure they thrive. Medical staff will evaluate your baby to see what degree of jaundice and anemia may occur. These conditions can be determined by physical exams, a special instrument called a bilimeter (this device has a sensor that is pressed against the baby's forehead to determine the degree of jaundice), and blood tests as needed.

A significant level of jaundice will be treated with phototherapy. Also known as light therapy, this is a non-invasive medical treatment in which a light source (often from fluorescent, LED, or halogen bulbs) is used to help the baby’s body break down bilirubin. When that happens, the bilirubin can be naturally eliminated from the body.

In rare cases, babies need more extensive interventions (such as IV treatments like transfusions or medications) for jaundice or anemia. Your healthcare providers will explain exactly what is needed for your baby if that occurs.

Most babies who are Coombs positive go home at the usual time. It is possible, however, that jaundice or anemia may recur once your baby is home. For this reason, your baby will need to be seen again by a member of your healthcare team within a few days of going home. Your infant's progress will be carefully assessed to ensure they are in good health.

It is also important to contact your healthcare provider if you notice any symptoms which could indicate Coombs-related jaundice or anemia. These include: pale skin tone; increasing yellowness of the skin and the whites of the eyes; poor feeding; fast breathing or trouble breathing; enlarged liver or spleen; full-body swelling; or excessive sleepiness.

Typically, Coombs-positive babies do not have any long-term problems. Because the mom’s blood and baby’s blood don’t mix after delivery, the reaction in the baby’s bloodstream slowly resolves. "The newborn naturally makes more new red blood cells, eliminating the issue," explains Dr. Ross.

A Word From Verywell

Hearing that your baby is Coombs positive can be confusing and upsetting. However, it is usually a mild and passing condition that does not impact your newborn’s current or future quality of life. Be sure to discuss test results after labor and delivery with your doctor and work closely with your baby's care team to determine how to keep your newborn healthy and comfortable if they receive a positive diagnosis.

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4 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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