RhIG for pregnant weak D patients

[ollie]

I have been reading your threads about weak D and am thankful for the chance to ask questions of the experts. I will try to keep brief, but I am happy to answer any follow-up questions you have. Forgive my non-technical, common language. I hope my ignorance does not get in the way!

 

I am 26 weeks into my fourth pregnancy (first one ended in miscarriage). For all of my pregnancies until this one (except for another exception I will explain) I have typed A+..."true" A+ with no weak D disclaimer. The exception I mentioned is one I just learned this morning, occurring in 2009 when I delivered my first-born via C-section. I was typed just before surgery as A-. My newborn was subsequently typed as A-, so no need for RhIG. Throughout pregnancy with my second-born, I was A+, as of 10/2013. Now, in this pregnancy, they (my OB's office) started telling me I am A- and will need RhIG. I questioned the "change" and was told that testing is more sensitive now, so this just showed up. When I started reading I found literature about weak D, so I asked more questions. Today I saw my results and they read A-, weak D+. All tests were from the same lab June 2008 - present. Additionally, my antibody screen was last week and came back negative.

Long story short(er), today I met with my high risk doctor (due to gestational diabetes) and she told me about an experience she had earlier this year with a patient just like me who had always typed Rh+. At that time, in February, the doctor called a blood bank in a larger city to see if RhIG was recommended. She was told it was not. I asked her if the testing so far has shown me to be weak D or if there is a chance I am partial D. She said she would like to find that out and it may require further testing if the hospital's lab did not or cannot do the further testing. She then called that same blood bank in the larger city and was told something more recent has come out to suggest treating all weak D types as Rh-.

Is anyone familiar with a change in recommendations? I saw someone on the board quote the 17th edition of AABB's Technical Manual as stating not to treat weak D patients as Rh-. Maybe there is a new recommendation after that? I listened to Dr. Connie Westhoff's podcast on bbguy.com from April 2016 and it supports treating weak D types 1 - 3 as Rh+. I am not trying to avoid RhIG altogether...just if it is not medically necessary; my baby's best interest is my greatest concern. Any insight is appreciated! In case it matters or anyone is interested, my mom is O+, dad A+, and husband O+. Thank you!

[StevenB]

This is directly from the AABB recommendations:

 

Consequences of current practice

Current practice for testing and interpreting Rh typing results appears to be highly successful in preventing alloimmunization to the D blood group antigen and Rh hemolytic disease of the fetus/newborn.⁴ However, there are unwarranted consequences associated with the practice of avoiding detection of weak D phenotypes, including unnecessary injections of Rh immune globulin and transfusion of Rh-negative red blood cells – always in short supply – when Rh-positive red blood cells could be transfused safely. If all pregnant women in the United States with a weak D phenotype were identified and their RHD genotype determined, an estimated 13,360 pregnant women who are currently managed as Rh-negative could be managed as Rh-positive, avoiding 24,700 injections of Rh immune globulin annually.¹

Recommendation of the Work Group

RHD genotyping is recommended whenever a weak D phenotype is detected by routine Rh blood typing of pregnant women and other females of childbearing potential. The Work Group rates this as strong recommendation, based on high-quality evidence from observational studies (1A).⁵ The Work Group also considered a recommendation to standardize routine laboratory methods for Rh typing that would increase detection of all patients with D variant phenotypes, including partial D, as well as weak D phenotypes. While desirable, such a recommendation is technically complex, likely controversial, and would divert the focus from our advocacy for phasing-in RHD genotyping when a pregnant woman’s routine Rh typing detects a serologic weak D phenotype. The immediate benefit of determining the RHD genotype of pregnant women with a weak D phenotype will be fewer unnecessary injections of Rh immune globulin.

It's common for hospital blood banks to treat potential mothers who type Rh (D) positive at the weak D phase of testing as Rh negative. It's not uncommon to hear stories similar to yours where a patient has been told one time they are D- and then another time, D+.  

If you want to get a better handle on your D typing, request that your hospital sends it out for molecular testing.  It can be expensive...ballpark $300...but it is the only way to determine whether or not you truly need Rh immune globulin.

[ollie]

Thanks for the response, StevenB!

[Malcolm Needs ☆]

SteveB's response is correct in all details, but just to put some more "flesh on the bones", I will add a little.

The reagents used to determine whether an individual is a "normal" D Positive, a "weak" D Positive, a "partial D Positive or a "normal" D Negative have improved in both sensitivity and specificity no end over the past few years and, as a result, situations in which you find yourself are now not uncommon (in other words, you have been found to be D Negative in the past, but are now being classified as a "weak" D Positive.

The situation is compounded by the fact that, until recently, individuals who have a weak or partial D antigen were regarded as "D Negative" when (potentially) receiving blood (in other words, when these individuals are patients), but as "D Positive" when giving blood as a donor.  I will not go into all the scientific and clinical reasons why this was so, not because I think that you will not be able to understand the reasoning (obviously, from your post, you are a very intelligent and well-informed lady), it is just that whole books have been written on the subject, and I would probably "crash the site" if I went into all of the fine detail.

In addition to the improvement in the reagents used, and the fact that we can now "look at" the RHD gene at a molecular level, population studies have indeed altered our views on who requires anti-D immunoglobulin prophylaxis, and who does not.

There have been two recent papers published (one this side of the "pond" in the UK, and one the other side of the "pond" in the USA) that have given guidance on who does, and who does not require this prophylaxis.  They are as follows:

Daniels G.  Variants of RhD - current testing and clinical consequences.  British Journal of Haematology 2013; 161: 461-470.

Sandler SG, Flegel WA, Westhoff CM, Denomme GA, Delaney M, Keller MA, Johnson ST, Katz L, Queenan JT, Vassallo RR, Simon CD.  It's time to phase in RHD genotyping for patients with a serologic weak D phenotype.  Transfusion 2015; 55: 680-689.

The authors of these two papers are the kind of people who are held in awe by individuals who work in our field - they are all experts!

I am fairly sure that your high risk doctor, and certain that the people whom she contacted at the larger blood bank will be familiar with one or both of these publications.

As SteveB said, if you are Weak Type 1 through to Weak D Type 3, it is not considered necessary for you to be offered anti-D immunoglobulin prophylaxis, whereas, if you are any of the other weak D or partial D types (of which there are now a huge number - but most extremely rare) it is considered necessary to make this offer.

From your obstetric history, and the fact that you have made no anti-D yourself, I would guess that you are amongst the Weak D Type 1 through to Weak D Type 3 group - BUT, that is very much a guess, and guessing is not in the nature of a scientist who works in this field!  Again, I agree with SteveB that it would be best to have your RHD gene "looked at" at a molecular level - albeit, the test is somewhat expensive.

[ollie]

Thank you for the kind words and wisdom. Moments ago I received a call from the high risk doctor who scheduled me for molecular testing. Just as an FYI for anyone interested or those who may run across this topic out of need in future, she volunteered the estimate of $450 and said it will take 5 - 7 business days to get results. Thanks again for the insight; I feel encouraged.