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Possible Auto-Jka


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I would most strongly advise you to send a sample, possibly even multiple samples throughout the pregnancy, to a Reference Laboratory.

As the patient is pregnant, there is the possibility that the Jk(a) antigen you are detecting is actually being expressed on the red cells of the foetus, and you are detecting it as a result of a foeto-maternal haemorrhage.  However, the Jk(a) antigen is not necessarily straight forward, as there are weakened forms of the antigen (and the Jk(b) antigen come to that) where there are amino acid substitutions remote from the site usually associated with the Jk(a) and Jk(b) antigens (280 of the mature protein).

In addition though, you have, obviously, to consider the health of the unborn baby who, even if the antibody does turn out to be a maternal auto-anti-Jka, may cause haemolytic disease of the foetus and newborn, albeit this will usually be be very mild.

I attach a PowerPoint which may, or may not help you in your decision to send a sample to your local Reference Laboratory (also tell them the ethnicity of the patient).

Interesting case - please keep us informed.

In Depth Lecture on The Kidd Blood Group System.pptx

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I would definitely refer this patient's sample to a reference lab for JK sequencing. As my friend Malcolm mentioned above, variants of JK antigens are not uncommon. The most common variant I've seen is caused by c.130G>C, which causes weakened expression of the Jka antigen. Interestingly, some patients with this variant would make anti-Jka, but I don't think we know much about the clinical significance of this antibody.

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I have a little bit more info on my case. In July she had a T&S done and the ABID was neg. She came through our ER as an MVA patient.  We use Capture R method (Echo) All panels show a perfect Jka. The throw off is the Complement is w+ after 5 min incubation. she antigen typed Jka+. Is this a true Jka or possible auto-Jka or varient. Patient was discharged same day. So no extra samples can be collected for send-off to reference lab. Our hospital does not handle OBGYN patients. 

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  • 2 weeks later...

A bit late for hopping in but. Another possibility suggests from the 2+ strength typing. Yes, it might just be heterozygous expression, but some techs will call a mixed field 2+. I know you said you didn't have transfusion history, but that's where I'd go first in workup before genotype. Try retic separation and retest.

If your patient had a low titer Jka, received unmatched units elsewhere either from this MVA as uncrossmatched units before transfer, or at an outside hospital between july and now, then came to you. I think it is feasible  you'd see this presentation.  DAT positive in c3d first as the Jka re-activates, an anomalous Jka+ result due to transfused cells but a clearly demonstrated anti-Jka. They could also have a weak expression variant of Jka, where they test positive but can form it. Or an auto Jka. But those are way less common than I think my boring scenario :-)


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