Anti-Kell Antibodies: Is My Baby Kell Positive or Kell 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 kell positive or kell negative. 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 (kell positive blood) then the babies who do not have the kell antigen (kell negative blood) are not in danger at all. Kell positive babies could be attacked by the antibodies during the pregnancy, so that is why it is important to figure out as soon as possible whether the baby carries the kell antigen or not (is kell positive or kell negative.)

There are several ways to find out if your baby is kell positive or kell negative. The first test that should be run is a simple blood test on the baby’s father. Since the mother is kell negative (her body would not produce anti-kell antibodies against itself so we know she isn’t kell positive) the only way the baby could possibly be kell positive is if the father is positive. The father needs to be tested for the kell antigen. If the father is kell negative then you can know for sure that the baby is kell negative and will not be harmed by the antibodies. If the father is kell 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 positive. If the father is homozygous then the baby has a 100% chance of being kell positive. So, if you know the baby’s father is homozygous for kell, you can be 100% sure that your baby is kell positive.

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 kell negative or positive. The most common way to find out is to wait until about 16 weeks and then have an amniocentesis which will show baby’s blood type. The only problem with the amniocentesis is that it does come with some slight risks and could even cause you to lose the baby, although the likelihood of that happening is minuscule. 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 is another, less invasive way to find out whether your baby is kell positive or kell 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. Wherever you are located, you should be able to send your blood off to the Netherlands to find out baby’s blood type 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. So, here is the information you will need to do the maternal blood test if you want. Print these forms off and take them to your MFM and you should be able to find out whether your baby is kell positive or kell negative without doing an amniocentesis. 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)