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Another RH antibody question


ssmith

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Good afternoon, I am a pharmacist in Philadelphia and currently pregnant (4th pregnancy, will be 3rd child) and was wondering if you smart folks could help me understand some lab results I received better. My story goes as follows. I am blood type O- and my husband is O+. We have 2 children both of whom are O+ as well. With both of those pregnancies I received the anti D antibody injection at 28 weeks and post-delivery. I then became pregnant in December 2014 but started to bleed pretty heavily February 27th 2015 at 11 weeks along. I went to the hospital at that time and as of then the pregnancy was still considered viable (closed cervix and visible HB on ultrasound). At that time they did an antibody screen that was negative and administered a 300mcg dose of Rhophylac, Rho(D) immune globulin, IM into my gluteus. Unfortunately that pregnancy did ultimately terminate on 3/5/15. I am fortunate to have become pregnant again and am expecting 2/4/2016. When I went in for my 28 week shot on 11/18/15 they drew blood for the antibody screen and then administered the injection. To my surprise the antibody screen came back positive. This is now almost 9 months after my latest anti D injection. Unfortunately I am told that they did not look at the titer of this result. I was sent back to the lab on 11/24/15 to repeat the test which of course came back positive since I had just received a dose of anti D 6 days previously. My OB has told me that the titer was 1:1 only and that they suspect that positive result 11/18 was from my previous dose of immune globulin. I really hope that this is the case, but am wondering what your experience with this is. Can you really remain antibody positive for 9 months?? I am 5'9, 150lb.

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Question:  Did you receive a dose of RhIG on 3/5/15 when the pregnancy terminated?  It is unlikely that after 9 months that the anti-D being detected is the result from the RhIG injection but I suppose not impossible.  Everyone's body is a little different and it just may take you longer to remove it from your system.

I would recommend having your husband Rh phenotyped, this will help determine the most likely odds of the current pregnancy being D+.  This would just be informational but it might alleviate some of the worry.  If your physician follows your pregnancy with additional titers of the anti-D and the titer rises, this would be pretty much confirmation that the anti-D is actually being produced by you and not the result of the RhIG injections.  Please do not think that having the anti-D is the end of the world.  My wife, a nurse of course, developed anti-D with our son.  Our daughter was effected by the antibody 4 years later when she was born which resulted in a double exchange transfusion but she is now 31 years old and has 3 children of her own. 

Good luck and please keep us posted.

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The package insert for Rhophylac specifically mentions the IM half-life as 18±5 days and that it's expected to see results at least 9 weeks post injection.

http://www.fda.gov/downloads/BiologicsBloodVaccines/BloodBloodProducts/ApprovedProducts/LicensedProductsBLAs/FractionatedPlasmaProducts/ucm119473.pdf

We'll routinely see 1+ reactions from presumed RhIg, three months post. Anything more than that and I get really curious.

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  • 3 weeks later...

Years ago I read that some RhIG anti-D could persist for as much as 6 months. We just had one recently that was weakly detectable after 4 or 5 months.  I do remember one strange case where it appeared to persist longer but it was 20 years ago and the details are hazy.  There is a test they can do on the mom's blood to detect fetal DNA and determine if the baby is Rh positive or not.  If your husband had one chromosome that was Rh negative but the other was positive, he would be Rh positive yet could pass the Rh negative to this baby.  Still, with already being in the 3rd trimester, even if there is real ant-D plus the shot, it is reassuring that the titer is so low.

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Thank you all for your responses. I have spoken more with my providers and they are pretty sure that the positive result is most likely real and not the result of the anti-d shot. The titer on 11/24 was <1 and when repeated on 12/17 it was not rising. Know one can say if its more likely from my miscarriage, or from this pregnancy, but I guess its not that important. They did an extra ultrasound to look at the baby and tell me everything looks good and that with levels so low there is likely not going to be a problem. I am keeping my fingers crossed! Only 5 weeks to go. Thanks again!!

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As there is no such a thing as a titer of less than 1, I'm guessing the titration result was actually nonreactive in the test phase they used for their titration study....which is good news for you and your baby!

Some labs report out titers as <1 when the first tube of the titration is nonreactive....not sure why as it is simply a negative result.  Again, that is good news for you and your baby.  I hope all goes well!

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On ‎1‎/‎5‎/‎2016 at 2:58 PM, StevenB said:

As there is no such a thing as a titer of less than 1, I'm guessing the titration result was actually nonreactive in the test phase they used for their titration study....which is good news for you and your baby!

Some labs report out titers as <1 when the first tube of the titration is nonreactive....not sure why as it is simply a negative result.  Again, that is good news for you and your baby.  I hope all goes well!

Sorry to disagree but there must be some level of antibody to have been detected in the first place.  Normal saline titrations are less sensitive than many detection methods.  Hence a titer of less than 1 is very accurate.  The antibody is there, there is just not enough of it to give a reaction in the 1st tube.  The reason most still perform saline titers is that was the method used when the studies were initially performed and, to my knowledge, that have been few if any subsequent studies using newer methods for titration studies.  :angered:

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No problem John, I enjoy a good discussion.  I agree totally with you when you say that there must have been some level of antibody reactivity for the antibody to have been detected in the first place. However when is comes to performing a titration for prenatal studies the only test of concern is the titration and it's results, not the PEG, LISS, Gel or Solid Phase tests that originally detected the antibody in question. Our physicians want to know whether their patient has an antibody, and if so how high is the titer.  In performing that test, I am only concerned with:  Does the antibody react in that test method and if so at what level.  If the antibody is not reactive in the 1:1 dilution, then the test is simply nonreactive and reported out as such.  That is a precise and accurate reporting of the test result obtained.  Anything else is speculation as we don't and can't test for a titer of <1. Obviously, as you have pointed out, there is some level of antibody present, but if a result is not tested for, and titrations do not test for <1 titers, then in my opinion it should not be reported as such.  Remember, this is a titration test...if there is a way to perform a titration of a sample to detect a titer of <1, I am "all in" on your position.  There are other tests available that will quantify the amount of antibody present, but they are not the test in question.

Thinking of this in other terms, when performing an antibody identification, it is not uncommon for us to use multiple techniques and there are times when the saline tube test is performed.  If nonreactive in saline, but reactive in other test methods, we would never report out that the antibody was present in the saline test phase, but at a level that was visually undetectable.  While we know the antibody is there in the patient's sample, it would not be accurate to report out something that we did not see. Essentially, that is what is being done when a result of <1 is reported in a titration test. 

As always in Blood Banking there are exceptions.  The endpoint for prenatal titrations is the last tube (or column, I suppose) that demonstrates 1+ reactivity.  That is a very specific parameter and it raises an interesting question:  If a titration reveals only reactivity in the 1:1 tube, but the reactivity is less than 1+, what is the titer?  In this situation, I would consider reporting out a titer of <1 because there is actually a visible result and a corresponding score would be reported.  However, I would also consider an accurate report to be "a titer of zero, score____" since as previously mentioned the endpoint for prenatal titrations is a 1+ reaction.  

Ultimately, a lab is going to report what they feel comfortable with.  In our region, we've had zero questions from physicians since we implemented reporting nonreactive titration studies in this manner. The same can not be said when a few of our techs were previously reporting the "<1" result.

 

 

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