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)


9 thoughts on “Anti-Kell Antibodies: Is My Baby Kell Antigen Positive or Kell Antigen Negative?

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  3. Hello. First off, thank you so much for sharing your journey with kell antibodies with all of us. It is such an amazing resource! I am pregnant with my 4th baby (2nd kell antibody- affected). I wanted to share with you a lab here in the US that does the same noninvasive cell free DNA testing to test for kell antigen using the mother’s blood at 9-10 weeks. It is called RAVGEN, and they are out of Maryland. I had contacted them with my last pregnancy (1st affected) and we decided we could not afford the testing, and decided to monitor the pregnancy as if baby was positive with weekly MCAs starting at 17 weeks, because I was also not comfortable with doing an amnio or CVS. Baby turned out to be Kell positive when tested at birth, but by the grace of God, never had any complications during pregnancy, only required 1 week in the NICU for hyperbillirubin, and never required any blood transfusions after birth either. Now I am about 7.5 weeks pregnant and my husband and I are trying to decide if we want to spend the money to get an answer one way or another (they charge $3000) or just take the same route we did last time. The website for the lab is, and the Kell antigen test isn’t even listed on their website, but if you call and speak with them, they will confirm they offer it. I have not looked into the one in the Netherlands that you provided information on yet. Can you tell me about that they charged for the test? Thanks again for sharing all of your experiences!! I hope this other lab will help other people in our shoes too!

    • I was able to find the price on the form you supplied when I opened it on my computer (it wasn’t pulling up on my phone). 750 Euros is a lot more affordable! Can you tell me about the process of doing the test with them? I am nervous about doing such an important test with someone so far away, and that I am not really able to talk to them about it. Thank you!

    • Hey, I’m so sorry I haven’t replied until now! I thought I did already but apparently I only replied in my mind. Anyway, from what I’ve read, there isn’t enough fetal DNA in the mother’s blood stream before 14 weeks to test baby accurately. Are you sure they test for the kell antigen? Also, you should come join the ISO moms group on Facebook if you are another kell mama!

      • Hi there!
        I am a Kell antibody momma with Kell+ dad. I recently gave birth to a Kell negative baby girl September 2019– our first born, I had an ectopic pregnancy in 2016 (Kell+ we are assuming). Although my baby girl is just over 3 months now, we are starting to talk about the future and potential for more kiddos… with the risk of carrying a Kell+ baby (my husband being heterozygous for Kell). I am interested in following along with your journey and want to learn how to advocate for our future little family members. The last MFM group I went to made it sound nearly impossible to get the noninvasive lab work done, thus reluctantly at 16 weeks we underwent amniocentesis (without complication thankfully).
        Is there anyway to get support where I am? I live in CT.
        Looking forward to learning more from your experiences.
        Thank you for what you do.

      • Hey Allison, I’m assuming you are the Allie that I just replied to on a different thread (I hope that’s you!) If you are on Facebook I suggest you come join our support group called Support for Antibodies in Pregnancy and follow The Allo Hope Foundation’s page on Facebook too. It’s our new nonprofit and soon our website will be up with tons of resources for Kell pregnancies

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