Anti-Kell Antibodies: Is My Baby Kell Antigen Positive or Kell Antigen Negative?

One of the first things that doctors and patients want to find out after a mother’s antibody screen comes back positive for anti-Kell antibodies is whether the baby is positive or negative for the Kell antigen. In fact, the rest of the treatment for the pregnancy and the baby’s outcome in the end often depends on the answer to that question.

Since anti-Kell antibodies are specifically programmed to attack the Kell antigen only, the babies who do not have the Kell antigen are not in danger at all. Babies who are positive for the Kell antigen could be attacked by the antibodies during the pregnancy, so that’s why it is important to figure out as soon as possible whether the baby carries the Kell antigen or not.

There are several ways to find out your baby’s antigen status. The first test that should be run is a simple blood test on the baby’s father. Since the mother does not have the Kell antigen (her body would not produce anti-Kell antibodies against itself so we know she is Kell antigen negative) the only way the baby could possibly have the antigen is if the father has the antigen and passed it down to the baby. The father needs to be tested for the Kell antigen. If the father is Kell antigen negative then you can know for sure that the baby is negative and will not be harmed by the antibodies. If the father is kell antigen positive then the next step is to find out if he is homozygous or heterozygous. Most men who have the Kell antigen are heterozygous which just means that the baby has a 50% chance of being Kell antigen positive. If the father is homozygous then the baby has a 100% chance of being Kell antigen positive. So, if you know the baby’s father is homozygous for Kell, you can be 100% sure that your baby has the Kell antigen as well.

If the baby’s father is heterozygous for Kell then it is harder to know the baby’s blood type since there is a 50% chance of being antigen negative or positive. The most common way to find out is to have an amniocentesis at 16 weeks, but it comes with the possibility of certain risks. Some doctors think that doing the amniocentesis increases the possibility of the baby’s blood and mother’s blood mixing, which could cause the antibodies to become more aggressive. There are also very rare complications that can happen after an amniocentesis that could ultimately end with the loss of the baby.

There is another, less invasive way to find out whether your baby is Kell antigen positive or Kell antigen negative. Dr. Moise recently shared this information with me and I am so excited to be able to share it with you. There is a maternal blood test that can be done in Europe that simply tests the mother’s blood to find out whether the baby is positive or negative for the Kell antigen; no risk to the baby. The test can be done at 14 weeks and is very accurate. I have included a study that shows the test’s accuracy. As far as I know, there has never been a wrong result. Occasionally the test result will come back “inconclusive” and they will ask you to send in your blood again for a retest. Wherever you are located, your OB or your MFM should be able to send your blood off to the Netherlands to find out baby’s antigen status with these forms and instructions I have posted below. Another Kell mama here in Alabama was able to send her blood off to the Netherlands to have it tested. She found out by 14 weeks that she was pregnant with a Kell positive girl and she was even able to get the cost of the testing covered by insurance. During my last pregnancy I brought all of these forms to Dr. Trevett in Atlanta and he was totally on board to try the test. I did the test at 14 weeks and found out several days later that my son was Kell antigen positive and my insurance covered the cost of the test. So, here is the information you will need in order to do the maternal blood test. Print these forms off and take them to your MFM and say you are interested in doing the non-invasive maternal blood test that is recommended by Dr. Ken Moise. I have also included the forms for anti-c and anti-E antibodies.

Instructions for Kell free DNA testing (updated)



Instructions for CcE free DNA testing (updated) (1)