A little bit about the Kell positive blood type

In Blood Will Tell I talked about the theory that Henry VIII had a Kell positive blood type, but in my quest to prevent innocent readers from slipping into an over-science coma I didn’t go into deep detail about it. . This post will provide a tad more information as to what it is exactly and how it is transmitted.

To have Kell positive blood means you have at least one of the Kell antigens on your red blood cells. This is in addition to the ABO blood groups that most people know about. There are apparently quite a few antigenic things that can be running around on the surface of your red blood cells. Who knew?

The funny thing about a Kell positive blood type is that the Kell antigen is passed on by a dominate gene, but even though it is dominate it is rare; less than 10% of the people in the UK have it. How can that be? Wouldn’t dominate genes … dominate?

Not necessarily, as it turns out.

Do you remember the Punnett Square from middle school biology classes? Okay, let’s call the Kell positive allele “K” and the Kell negative gene “k”. Everyone would have two of these genes, so people with Kell positive blood are either “KK” or “Kk”, and people with Kell negative blood are “kk”. Now, what would happen if a Kell positive person reproduced with a Kell negative person? Their children have the potential genotypes of:

Kk Kk
Kk Kk


Kk Kk
kk kk


We know two things from these squares and the fact Kell positive blood is rare. First, people who are Kell positive are most likely to be Kk instead of KK Why? Because there is a more than 90% chance that one of their parents was Kell negative, and thus had only k genes to bring to the party. Secondly, when Kell positive people with the typical Kk genotype reproduce with one of the Kell negative (kk) majority, each child has only a 50/50 chance of being Kell positive.

Let’s look at the hypothetical example wherein a Kk/kk couple has four children to see what can happen:

1) They have no K postive offspring. Now, we’ve all met families where all the kids were the same gender, so you know 50/50 doesn’t mean it will always split down the middle between two outcomes. Thus, all four  children could be kk and Kell positive blood would disappear from their genetic line. Unless one of the offspring reproduces with a Kell positive partner (which is a less than 10% chance) no grandchildren will be Kell positive, and so on forevermore.

2) All four kids are K positive. If all four children are girls, and they each are Kk, then Kell positive blood is very likely to show up in the grandchildren. However, if all four children are boys then the Kell gene is much less likely to turn up in the grandchildren, because every pregnancy after the FIRST one will only survive if it is Kell negative (kk). So if every boy grew up, married, and had 4 kids himself … then no more than 4 out of the 16 grandchildren could possibly have the Kell positive gene. Since there is only a 50/50 of a first born getting the K gene, maybe only 2 out of the 16 hypothetical grandchildren will be Kell positive. Or maybe none of them will be.

Basically, every time a Kk person has a male child, the odds of the K gene making it to the next generation is lessened. (Well, it used to be like that before modern medical treatments that will keep a Kell positive fetus alive inside a Kell negative mother. Kell may become more common now. Ask me again in 150 years.)

Moreover, random chance can make a dominate gene go bye-bye even when the dominate gene doesn’t cause the death of many offspring who inherit it. Take brown eyes and blue eyes, for example. For simplicity’s sake we’ll say brown eyes are “B” and blue eyes are “b”. This means we can use the Punnett square again and see the genotypes of the offspring of a brown-eyed person (BB or Bb) and a blue-eyed person (bb).

Bb Bb
Bb Bb


Bb Bb
bb bb

Let’s say mom has brown eyes of BB and dad has blue. Every one of their kids will have brown eyes because of the B, but they will all be carrying the blue b as well. If mom’s brown eyes are Bb, then some of the kids might be blue-eyed, but the brown-eyed kids are all going to be carrying a recessive too. See? Once you get a bb in the mix those little b genes are lurking in every gonad. If those offspring marry blue-eyed (bb) people, then more of the grandkids will be blue-eyed too. Once a person has expressed recessive genes, there are NO dominate genes to pass on to their kids. Dominate browns can easily be hiding secret blue genes (insert blue jean joke here) but the brown B is gone once the recessive have the field. If two couples, let’s name them Ted (BB) & Alice (bb) and Bob (bb) & Jane (Bb), have children who marry each other then it is possible that all their grandchildren can have blue eyes in spite of the fact that two grandparents have the dominate brown-eyed gene. Of course, all of them could have brown eyes – it depends on the roll of the genetic dice when Mr. Sperm meets Ms. Egg.

There you have it. A very simplified version of how a dominate gene (especially one that is harmful under certain conditions) can wind up being in only a small minority of a population.

It really was just bad luck that Henry (in theory) had a Kk genotype. How do we know that if he was Kell positive, Henry had to be Kk and not KK? Because the New Year’s Boy survived for a few weeks and Mary lived to adulthood. If the King had not had a “k” gene to give them, they would have died in utero or a few hours after their birth like their poor siblings did. QED – Henry had a Kk genotype.

But how did Henry get that Kell positive gene? Well, tune in next post for the exciting adventures of Genealogy Quest!

35 comments for “A little bit about the Kell positive blood type

  1. Belinda
    April 19, 2013 at 11:23 pm

    I contracted the Kell antibody because of a blood transfusion I had after my 1st pregnancy which was a c-sec. 2nd pregnancy I had kell antibodies but since Dad is Neg and my pregnancy went on as normal. My question is will my son have any Kell at all? I would hate for his future wife to go through the scare I had, or since Dad is Neg & my pregnancy was “normal” is my son kell free?

    • April 20, 2013 at 12:34 am

      The good news is that a simple test will tell you if your son has it … and the better news is that I think it is highly unlikely. The Kell antibody was introduced into your system, and Daddy is also negative, so as far as I can tell there is no way your son inherited the genes to produce Kell antigens. QED — he’s Kell negative. Hope that helps!

      • Belinda
        April 24, 2013 at 9:11 am

        Thank you very much, I had quite the scare and was so mad about the whole thing . Thank Goodness all is ok, but now I don’t think I can donate Blood anymore which is sad as I am
        O-Neg….I appreciate your response have a wonderful day.

  2. Lindsey
    July 24, 2013 at 10:14 pm

    I had two miscarriages a year ago. And after my second one (a week later) I had blood work done and it came back that I had Anti Kell. But my levels of it were too weak to show up on the titer level. Well, here I am a year later and I had blood work done the other day and my blood showed NO kell. My OB says my blood is normal. Is that possible? Or if I get pregnant again will it come back?

    • July 25, 2013 at 10:17 am

      I am not a medical doctor, but I will give you all the information I have. Just remember that my opinion is likely to be inferior to the doctor’s on any point of difference.

      First, I think s/he is correct about your blood work being normal. If there is no Kell positive fetus/embryo in your uterus then your body won’t be making the anti-Kell stuff to attack it with, so there shouldn’t be enough to show up.

      As for the next pregnancy … luck will play a big part of it. My hubby is a type 1 diabetic, and (although the public doesn’t seem to know this) blood sugar levels effect spermatogenesis. That means the partner of the diabetic man is more likely to have miscarriages because the sperm that fertilizes the egg may be “broken”. I knew this, and understood it rationally, but when I had two miscarriages in a row I was still devastated because the heart tends to ignore the brain. Thus, I do have some inkling of what you are going through and you have my deepest sympathy.

      I wish I could tell you it would be a-okay from now on but it will depend on several factors. The good news is that your husband is EXTREMELY likely to have a non-Kell gene as well as a Kell gene to give an embryo. If you get a non-Kell sperm then (if all else is normal) you will have a healthy pregnancy and a hearty little baby at the end of it without any big medical interventions. If you do get a Kell positive fetus then there ARE things the doctor can do to save the pregnancy. Just make sure s/he remembers/knows your last pregnancy had this issue. There is unlikely to be any insurmountable obstacles preventing your from having children … it may just take longer and be harder.

      After losing two pregnancies, I was blessed with three healthy babies in a row. I sincerely hope all of your subsequent pregnancies bring you such joyful results as well!

  3. Lindsey
    July 26, 2013 at 9:50 pm

    Thank you for the advice Kyra! And that’s awesome you have 3 precious babies! Thanks for the positive thoughts as well :) will keep you posted!

  4. BirdNerd
    August 15, 2013 at 8:18 am

    Help. I am pregnant and diagnosed as having the anti-Kell antigen. We have been trying for years to have a 2nd baby, I have had several misscarriages so those were probably Kell positive babies. I am terrified but there are no support groups for Mom’s struggling with this since it is so rare. Looking for a shoulder to cry on while I go through this process.

    • March 13, 2014 at 8:28 am

      Dear BirdNerd,

      This got caught erroneously in my spam filter. I am so sorry about the delayed reply. I sincerely hope this reply finds you well and delivered of a healthy second child!!!!!

  5. amber
    September 8, 2013 at 11:42 pm

    Okay, I’m trying to remember science in middle school, having a tough time. So of you are Kk, then are you positive or negative? We are waiting for the results of my husbands bloodwork, I have Kell and Kidd antibodies. Really wish they would screen blood for this when someone donates, it is scary for women to have to go thtough this. I have been wondering if the tables could be turned, could the father produce a K positive baby and mom be k negative. Would the baby’s blood attack moms blood? Not sure why this came to mind but it dis, perhaps I’m trying to occupy my time while we wait for the blood work. I wish we had the $ for the full bloodwork for my husband, as we are only finding put of he is positive or negative for the antigens. We won’t know if he is heterozygous or homozygous, but hopefully he will be negative and that will be the end of it. What I am also wondering is are the Kell antibodies only detectable if the baby in fact has the antigen, or are they detectable even when basically dormant.

    • Ashley
      January 29, 2015 at 8:17 pm

      I wonder if there is anyway that we can change this? I too became anti-kell from a blood transfusion. And I am now pregnant waiting in test results. I have some friends that I am trying to work with to petition some how to get blood Donors screened for kell. Hoping that it will help young girls/women of childbearing age. It could be prevented if they would just screen.

      • Debbie
        February 16, 2015 at 7:14 pm

        I agree with the petition. I’m 34 years old. At 25 I gave birth to my first child and had a blood transfusion where I than became KK positive Kell antigen. I didn’t find out until i was preganat with my second child five years later. My doctor explained my problem to my husband and I, where I cried until his results came back negative. For a few years I’ve been wondering how many other women.. But after reading this I can’t believe how this problem it has become a nightmare to many moms.
        Debbie from NY

        • Jessica
          March 23, 2015 at 4:23 pm

          I’m 35 weeks and I found out about two weeks ago that my original bloodwork was positive for the anti kell. After my first born I had a transfusion that obviously contained the Kell antibodies. Today my husbands blood work came back as negative just as your husbands did. Was that the end of the drama? Did the doctors have to take any extra special precautions or anything like that? I do have slight anemia which they believe is caused by the kell. I feel like even if the baby is negative and so is my husband that there could still be problems with myself?

  6. amber
    September 8, 2013 at 11:44 pm

    Never mind about the question, I asked it wrong can a Kk pass only positive onto a child or can they still pass the negative too? Maybe it is on your post it is pretty late.

    • September 9, 2013 at 9:18 am

      If your husband is Kk then the babies could have the Kell antigen. If he is KK then they will definitely have the Kell antigen. If he has kk, then it’s all clear because he cannot give any offspring the Kell antigen gene. If it is a first pregnancy, then the mother’s body will not attack the fetus even if it is Kell positive. However, any subsequent pregnancies will be threatened if the fetus is Kell positive. If the mother is Kell positive but the dad is not Kell positive, then the fetus will be unharmed by the mother’s body either way. I hope you get good news!!

  7. Lisa Sullivan
    November 27, 2013 at 5:07 am

    I have just found out that I had K antibodies in my blood tests in my second pregnancy. I didn’t have them in my first and haven’t had a transfusion. When my husbands blood came back, he is kell negative. He is 100% definitely the father. How have I got these antibodies?

    • November 27, 2013 at 10:49 am

      Well, my first instinct is to wonder if you got a false positive or if your husband got a false negative. If you had the antigens, it would just mean you are Kell positive and it would pose no threat to your pregnancy, but antibodies mean that your blood has been exposed to the Kell proteins. Did they test your husband for both K1 (Kell) and K2 (Cellano) genes, or was it just a blood test? I am so sorry that I can’t be more help. I’m an anthropologist, and maybe a specialist in genetic transmission could help you. Any university would probably have such an expert that you could email.

      Wishing you all success!!!

    • Suzi
      June 20, 2014 at 7:07 am


      Did you ever gather any more information on where your antibodies came from? I am currently in the same situation and am totally baffled!
      I have K antibodies, my husband is apparently negative with kk. He is the father of my two boys, and this third pregnancy where these antibodies have shown up for the first time. We also don’t know if the baby is definitely negative if antibodies have shown up in the first place….

      Any suggestions?


      • June 20, 2014 at 8:19 am

        Frankly, I am baffled as to how the antibodies got into your system without a blood transfusion or Kk hubby. I would recommend retesting Dad because a false negative is the most likely explanation.

  8. susan m
    December 14, 2013 at 8:49 am

    Any ideas on where the pos K people are from?? Me, and ALL of my family, sis, mom, aunts are all K pos, because a blood company wanted us to give blood for money to make diagnostics……. we cannot trace the family tree and were wondering if there was a spot in the world it showed up with more incidence, helping us to know our roots?

    • amber
      December 31, 2013 at 5:25 pm

      People who have that blood have golden blood to me. I can’t have blood transfusions unless they have an exact match as me. I almost died having my son. My baby girl is due in 3 months, even with a c section I can bleed out. I am A- with Kell and Kidd antibodies. It is rare my midwife said to find blood compatible with Kell.

  9. Melanie
    March 12, 2014 at 3:40 pm

    Hi I have 8 children when I was 20 weeks pregnant with baby number 9 they told me I had kell antibodies and during delivery some of my daughters blood must of leaked back into my system to create antibodies , my husband is father to all my children so is it just pure luck we haven’t had any issues till now? My hubby tested positive for kell antigen and is homogenous for kell so all our kids are kell positive , can you please explain how he is homogenous for kell antigen , my pregnancy is now 34 weeks and my tillers have remained stable at 1:28 but today have doubled , baby shows no signs of anaemia via mca scan and no signs of hydrous but they want to deliver in 2 weeks , what does the rise in antibodies mean?

    • March 13, 2014 at 8:24 am

      Hi! First, congratulations on your healthy family! First, homozygous Kells (KK) is very, very rare. Did they double check? If he is actually heterozygous (Kk) then yes, you were VERY lucky but not beyond rational expectations. If he is indeed homozygous then I have no idea whatsoever why your other pregnancies didn’t have severe complications. I think it would have to be a deficient immune response by your own body and I have no knowledge about that topic. I’m sure a proper medical doctor would be able to figure it out. I suggest you get one of the boys (other than the first born) and have him tested for Kell antigens. If they are Kell negative, you’ll know the test for your husband was off a bit and that he is Kk, not KK. That means all the children except for the first, your daughter, and #9 will be almost axiomatically Kell negative. They would have no K gene to cause their wives any distress during pregnancy. Yay! Your first born son will need to be tested to know for sure. Your little girl must be Kell+ and #9 must be Kell+ or your body would not be making antigens. Your daughter will not be troubled by Kell+ because her body will not attack the fetus either with or without Kell. If #9 is a boy, every pregnancy after his wife’s first will need to be watched by an OB/Gyn who knows she might be carrying a Kell+ fetus — unless his wife is K+ too, which is rare. PLEASE let me know what the results were if you get a son tested for Kell!! I am very, very glad baby #9 is doing well and I hope he or she has zero problems before, during, or after the birth.

  10. Melanie
    March 12, 2014 at 3:45 pm

    I have 7 boys and 1 girl baby number 9 gender not yet known what does being kell positive mean to them and their future offspring please

  11. January 6, 2015 at 12:45 pm

    I am little k cellano negative O positive is it hard for me to get blood if needed

  12. January 12, 2015 at 3:06 pm

    please reply as I will need a operation soon I am little k negative o positive

    • February 2, 2015 at 1:33 pm

      I am sorry that this got trapped in my comment filter and I just saw it. Sadly I am unsure as to what I could do to help ….

  13. Ashley
    January 29, 2015 at 8:36 pm

    Ok so I am pregnant with baby 4. Baby 3 I had to have a c sec and transfusion. Now I have anti-kell showing up on my blood test. They did a titer all they told me was that it is an 8 ?….

    My husbands waiting to get results to find out if he is kell pos.

    Would my body make the anti-kell show up even if daddy is negative?

    Does anti-kell only show up on blood work when it’s fighting baby….who is kell positive?

    (I’m not sure I even asked these questions correctly)

  14. Debbie
    February 16, 2015 at 7:30 pm

    I became Kell antigen positive after receiving a blood transfusion while giving birth. Will this be a health problem for me later in life. Could I get severe anemic? There’s really not much information out there for this problem that many young moms face today.
    Debbie , New York.

    • March 4, 2015 at 3:06 pm

      As far as I know (and remember I’m not an MD so if your doctor says otherwise listen to him/her!) you should be fine. Odds are good your body will always make enough red blood cells for you. Hope that helps!!!

  15. Donna
    February 25, 2015 at 4:58 pm

    After giving blood twice I recieved a letter letting me know I was A+ kell. For me this was a big shock, I’ve not had any blood transfusions and have had 2 very healthy boys. I have read a few articles on kell but must have my blonde head on as I can’t get my head round it.

    • March 4, 2015 at 2:56 pm

      Okay, the GOOD news is that as a K+ woman your pregnancies will never be effected. Your body won’t attack a Kell+ baby because it is the SAME and it won’t attack a Kell- baby because there is no antigen there to set it off. The BAD news is that if either of your sons have your blood type then their partners might (and it is a big if considering genetics) have issues IF the partner is a normal K- and IF the second fetus is K+. You can get the boys tested now and then they can warn their wife/partner if and when pregnancy is a possibility. The best news is that there is a lot they can do nowadays to keep a Kell+ fetus healthy until birth. Remember, YOU are here and you were obviously a Kell+ fetus at one point. Does that help clear things up at all?

  16. Melissa
    February 28, 2015 at 11:37 pm

    So, you touched on my question in another comment but I just want to ask in more detail because I’ve been able to find no information on the web…My brother is Kell positive and after his wife had their first child, she developed the antigen. They were pregnant again but lost the baby at 23 weeks due to the problem. :( I understand how it works when the mother is negative and the father is positive. However, I am currently pregnant and am wondering how it could possibly effect my pregnancies. What happens if the mother is Kell positive and the father is Kell negative? Like the punnett square shows, I have a 50% chance of passing it on to baby. I’m assuming if I’m positive and fetus is positive there is no problem. What happens if I don’t pass it on to the fetus and I’m positive but fetus is negative? Thanks for your help!

    • March 4, 2015 at 3:02 pm

      First, I am sorry for the loss your brother and SIL went through. I hope their next fetus is Kell- or that the Ob/Gyns can do more to help and keep the fetus safe until old enough to be born.
      That being said, a Kell+ woman will not have any problems with pregnancy because of her blood type. If your fetus is Kell+ your body will not attack it because it is the same as your blood type. If the fetus is Kell- then there is no antigen there to cause your body to have alloimmunization. Either way, your babies are safe from issues due to Kell. However, if you have a Kell+ son and his future partner is Kell- then they need to give her a doctor a heads up when/if she gets pregnant.

      • Melissa
        March 6, 2015 at 3:35 am

        Thanks for writing back and for explaining how the Kell blood type will effect me. I appreciate your help. Cheers.

      • Jessica
        March 23, 2015 at 4:31 pm

        If I am Kell +, & My husband is Kell -, babies + or – is currently unknown . . Am I at any risk myself during my pregnancy? I’m 35 weeks and have slight anemia as I did with my 1st baby. I have Orthostatic Hypotension and after my 1st baby girl I ruptured a vein causing me to lose blood when I was already anemic and had a lowish blood count. I did have a transfusion. Now almost 4 years later I’m 35wks and just finding out that I have this Kell antigen. I’ve heard stories of Kell making you severely anemic, and causing women to bleed out even in cases where baby is negative. Am I at risk for anything because of this antigen??

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