Jump to content
PathLabTalk

Weak D Testing - Cord Blood Evaluation


Recommended Posts

Hello, 

My facility is trying to determine whether or not it is necessary to perform weak D testing on Rh negative cord bloods (Rh performed in gel). As far back as our LIS can go, there has never been a weak D identified for a cord blood that originally tested as Rh negative in gel. 

I am unsure of how to interpret TRM.40780 "Maternal RhIG candidacy assessment must include the identification of weak-D phenotype newborns". 

I know there are previous threads on this topic, but most are quite old. Currently, do you perform this testing at your facility? Any input is appreciated. Thank you!

Link to post
Share on other sites


1 hour ago, Kathyang said:

  We use gel on Cord Bloods but it doesn't detect DVI. We still perform weak D testing on all negative cord bloods.

It is not the gel test that does not detect Partial DVI, it is the monoclonal anti-D blend in the gel that you use that does not detect those four Partial DVI types.

Link to post
Share on other sites
1 hour ago, kaleigh said:

Hello, 

My facility is trying to determine whether or not it is necessary to perform weak D testing on Rh negative cord bloods (Rh performed in gel). As far back as our LIS can go, there has never been a weak D identified for a cord blood that originally tested as Rh negative in gel. 

I am unsure of how to interpret TRM.40780 "Maternal RhIG candidacy assessment must include the identification of weak-D phenotype newborns". 

I know there are previous threads on this topic, but most are quite old. Currently, do you perform this testing at your facility? Any input is appreciated. Thank you!

I am a worker from/in the UK, but if TRM.40780 says, "Maternal RhIG candidacy assessment must include the identification of weak-D phenotype newborns", that is exactly what it means.  It doesn't say "should" instead of "must", and it doesn't say, "until you give up because you are bored, because you have never found one"!

Yes, such types are rare, but they do happen, and they can cause the mother to produce an anti-D (of sorts).  These antibodies are not usually particularly clinically significant in terms of further pregnancies - but the word "usually" is the important one in that sentence.

The only thing I would say is, WHEN you do detect a newborn who tests as weak-D positive, don't forget to test the mother too; she may also express the same weak-D type (but, depending upon your laboratory's policy, may not have been tested as expressing this type during the pregnancy), and, if she does, she doesn't need the anti-D immunoglobulin (which, remember, is a human-derived blood product, which may contain a novel blood-borne virus type about which we know nothing - YET).

Link to post
Share on other sites
5 hours ago, YorkshireExile said:

We also test for Weak D`s on Rh negative babies of Rh negative mothers. The CAP TRM: 40780 says you have to anyway. I think in about 13 years I have seen two babies that were Weak D positive.

You have NEVER seen a baby who is Weak D Positive.

There is no such thing as anti-Weak D!  May I suggest that you read Stratton F.  A new Rh allelomorph.  Nature 1946; 158: 25-26, followed closely by Race RR, Sanger R, Lawler SD.  The Rh antigen Du. Ann Eugen (Camb) 1948; 14: 171-184, which will explain why there is no such thing as anti-Weak D.

I appreciate that CAP seem to be incapable of using correct terminology, but that does not mean that we should all descend to their levels of incompetence.

Sorry for the "vent", but this wrong terminology has gone on now for 72 years; six years more (embarrassingly) than I have been alive!

I'm sorry if this sounds like a personal RANT against you. YorkshireExile; it is certainly not meant as such.  It is just a general rant against people who use poor nomenclature because they don't learn even the basic history of their own specialist subject - and that includes the people who SUPPOSEDLY make sure the rest of us "follow the rules"!

Edited by Malcolm Needs
Entirely my fault. Got upperty AGAIN.
Link to post
Share on other sites

Limitations to the FHM RapidScreen Test
1. For correct interpretation of the test results, the test must be performed on the blood of a
known D-negative mother of a recently delivered D-positive child. If the infant's red blood
cells possess a weak D antigen or partial D antigen, the test may not detect a fetomaternal
hemorrhage exceeding 30 mL of whole blood.

Link to post
Share on other sites
On ‎6‎/‎12‎/‎2020 at 1:11 PM, Malcolm Needs said:

It is not the gel test that does not detect Partial DVI, it is the monoclonal anti-D blend in the gel that you use that does not detect those four Partial DVI types.

We use gel, and as other are doing, if Rh Neg with Gel, we test for Weak D. 

I must add this caution: Be mindful of what your Anti-D is capable of detecting.  Some purposely do not detect DVI.  You want to detect DVI on these newborns to determine the possibly of immunizing an Rh-Neg mother, i.e. Is she a candidate for Rh-Immune Globulin. 

n.b. Currently, we are using an Anti-D reagent that detects DVI (as well as other Weak D)  at Immediate Spin, so the 'Weak D typing' is very quick and simple.

Edited by Joanne P. Scannell
Link to post
Share on other sites
53 minutes ago, Joanne P. Scannell said:

We use gel, and as other are doing, if Rh Neg with Gel, we test for Weak D. 

I must add this caution: Be mindful of what your Anti-D is capable of detecting.  Some purposely do not detect DVI.  You want to detect DVI on these newborns to determine the possibly of immunizing an Rh-Neg mother, i.e. Is she a candidate for Rh-Immune Globulin. 

n.b. Currently, we are using an Anti-D reagent that detects DVI (as well as other Weak D)  at Immediate Spin, so the 'Weak D typing' is very quick and simple.

True Joanne, it is very fast, but one of my points about this is that, when a baby is found to have a Weak or Partial D (such as Partial DVI), it would be good practice to test the mother for Weak or Partial D expression, if this has not already been done, because she may be the source of the mutant gene leading to the baby's Weak or Partial D type.  If she is the source, then it is a moot point, to say the least, as to whether she should or should not be exposed to a human-derived blood product that may, for all we know, be harbouring novel virus that may be transfusion-transmitted.  AT the very least, she should have the risk, albeit very low, explained to her before she is given the anti-D immunoglobulin.

Link to post
Share on other sites

Yes, you should perform the weak D test. The fact that you haven't seen a positive yet doesn't mean you won't see one tomorrow. If mother is truly D negative, she has been exposed to D antigen and needs to receive RhIG. As Monique pointed out, it changes how you determine RhIG dosage as well. We see 1 to 3 babies each year that have positive weak D tests out of the 150 or so tests we do, so they are out there. Actually...it's kind of fun to find them in a total geek way.

Link to post
Share on other sites
23 hours ago, Malcolm Needs said:

True Joanne, it is very fast, but one of my points about this is that, when a baby is found to have a Weak or Partial D (such as Partial DVI), it would be good practice to test the mother for Weak or Partial D expression, if this has not already been done, because she may be the source of the mutant gene leading to the baby's Weak or Partial D type.  If she is the source, then it is a moot point, to say the least, as to whether she should or should not be exposed to a human-derived blood product that may, for all we know, be harbouring novel virus that may be transfusion-transmitted.  AT the very least, she should have the risk, albeit very low, explained to her before she is given the anti-D immunoglobulin.

Good point ... but most MDs give the RhIg when Weak/Partial D is reported because they don't understand the situation even if we try to explain it to them.

Link to post
Share on other sites
  • 2 weeks later...

Can I just point out here that no one serological test, or even combination of tests will detect all weak / variant Ds .  And that includes women who test D+ but actually have a partial D and may make anti-D antibodies.  It is SO important to know your reagents, and know what your anti-D reagents will and will not detect

Link to post
Share on other sites
  • 2 weeks later...
13 minutes ago, Malcolm Needs said:

WHY?

You know why Malcolm. If mom is Rh negative and baby is Rh positive, mom has 16% chance of developing anti-D after her first pregnancy. Moms with partial D can be classified as Rh Positive, but may still require RhIg to prevent HDFN.  Our policy is to do weak D testing on all newborns who test D negative when we do the ABO/Rh forward typing. 

Link to post
Share on other sites
9 minutes ago, diplomatic_scarf said:

You know why Malcolm. If mom is Rh negative and baby is Rh positive, mom has 16% chance of developing anti-D after her first pregnancy. Moms with partial D can be classified as Rh Positive, but may still require RhIg to prevent HDFN.  Our policy is to do weak D testing on all newborns who test D negative when we do the ABO/Rh forward typing. 

Sorry, but no.  Mother's who have a weak D phenotype can, VERY rarely, produce an alloanti-D, but if they have a partial D phenotype, they are automatically classified as D Negative (unless they are Partial DIII, in which case, unless genotyping is performed, it is impossible to tell, as ALL monoclonal anti-D reagents react strongly with red cells that are partial DIII).I see that you are an SBB student.  From this, I deduce that you either work in the USA, or follow their guidelines, and so, no doubt you will have read 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 serological weak D phenotype.  Transfusion 2015; 55: 680-689, and the recent update Willy A. FlegelGregory A. DenommeJohn T. QueenanSusan T. JohnsonMargaret A. KellerConnie M. WesthoffLouis M. KatzMeghan DelaneyRalph R. Vassallo, Clayton D. SimonS. Gerald Sandler.  It's time to phase out “serologic weak D phenotype” and resolve D types with RHD genotyping including weak D type 4.  Transfusion 2020; 60(4): 855-859, which will show you that, what you have said is wrong, vis-a-vis maternal D typing.

Link to post
Share on other sites
3 hours ago, Malcolm Needs said:

Sorry, but no.  Mother's who have a weak D phenotype can, VERY rarely, produce an alloanti-D, but if they have a partial D phenotype, they are automatically classified as D Negative (unless they are Partial DIII, in which case, unless genotyping is performed, it is impossible to tell, as ALL monoclonal anti-D reagents react strongly with red cells that are partial DIII).I see that you are an SBB student.  From this, I deduce that you either work in the USA, or follow their guidelines, and so, no doubt you will have read 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 serological weak D phenotype.  Transfusion 2015; 55: 680-689, and the recent update Willy A. FlegelGregory A. DenommeJohn T. QueenanSusan T. JohnsonMargaret A. KellerConnie M. WesthoffLouis M. KatzMeghan DelaneyRalph R. Vassallo, Clayton D. SimonS. Gerald Sandler.  It's time to phase out “serologic weak D phenotype” and resolve D types with RHD genotyping including weak D type 4.  Transfusion 2020; 60(4): 855-859, which will show you that, what you have said is wrong, vis-a-vis maternal D typing.

I never said mother with weak D. Come on Malcolm, you know I didn't say mothers with weak D. 

Link to post
Share on other sites
1 minute ago, diplomatic_scarf said:

I never said mother with weak D. Come on Malcolm, you know I didn't say mothers with weak D. 

 

3 hours ago, Malcolm Needs said:

Sorry, but no.  Mother's who have a weak D phenotype can, VERY rarely, produce an alloanti-D, but if they have a partial D phenotype, they are automatically classified as D Negative (unless they are Partial DIII, in which case, unless genotyping is performed, it is impossible to tell, as ALL monoclonal anti-D reagents react strongly with red cells that are partial DIII).I see that you are an SBB student.  From this, I deduce that you either work in the USA, or follow their guidelines, and so, no doubt you will have read 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 serological weak D phenotype.  Transfusion 2015; 55: 680-689, and the recent update Willy A. FlegelGregory A. DenommeJohn T. QueenanSusan T. JohnsonMargaret A. KellerConnie M. WesthoffLouis M. KatzMeghan DelaneyRalph R. Vassallo, Clayton D. SimonS. Gerald Sandler.  It's time to phase out “serologic weak D phenotype” and resolve D types with RHD genotyping including weak D type 4.  Transfusion 2020; 60(4): 855-859, which will show you that, what you have said is wrong, vis-a-vis maternal D typing.

We don't do Weak D testing on adults, unless if they are donating blood. 

Link to post
Share on other sites
5 hours ago, Malcolm Needs said:

Sorry, but no.  Mother's who have a weak D phenotype can, VERY rarely, produce an alloanti-D, but if they have a partial D phenotype, they are automatically classified as D Negative (unless they are Partial DIII, in which case, unless genotyping is performed, it is impossible to tell, as ALL monoclonal anti-D reagents react strongly with red cells that are partial DIII).I see that you are an SBB student.  From this, I deduce that you either work in the USA, or follow their guidelines, and so, no doubt you will have read 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 serological weak D phenotype.  Transfusion 2015; 55: 680-689, and the recent update Willy A. FlegelGregory A. DenommeJohn T. QueenanSusan T. JohnsonMargaret A. KellerConnie M. WesthoffLouis M. KatzMeghan DelaneyRalph R. Vassallo, Clayton D. SimonS. Gerald Sandler.  It's time to phase out “serologic weak D phenotype” and resolve D types with RHD genotyping including weak D type 4.  Transfusion 2020; 60(4): 855-859, which will show you that, what you have said is wrong, vis-a-vis maternal D typing.

I have never heard of your references. The main texts for my course includes AABB technical manual by Fung, Harmening's Modern blood banking and transfusion services, and AABB's Standards for blood banking. I am only a part time SBB student, I work full time as a Medical Technologist. This is my final semester. You don't need to show me references I never heard of,  I am certain you are right.  Mom's with PARTIAL D (NOT WEAK D, WE DON'T TEST WEAK D FOR MOMS) can be typed as Rh positive, but still may form Anti-D when exposed to Rh positive red cells from baby(Modern Blood banking and transfusion services, Harmening, 7th Ed. p. 160). 

Edited by diplomatic_scarf
fixed spelling before Malcolm insults me for spelling error
Link to post
Share on other sites
  • 2 weeks later...

  "It's time to phase out “serologic weak D phenotype” and resolve D types with RHD genotyping including weak D type 4. "

 

I realize I'm a little late to the thread but thought I would share our practices at our US facility. newborns are only tested for partial D when they are initially Rh Negative. We use capture method and the ECHO does a fine job picking up weaker expressions of D at the RT phase of testing. I recently sent our 1st maternity sample out for molecular typing and plan to incorporate mandatory molecular as a reflex test in the future when the anti-D test result is 2+ or weaker. The 1st sample came back as an RH type 3 and as such would not be eligible for RhIG by the new recommendations. 

 always interesting to see what other facilities do for their maternal testing and I appreciate all the insight on the forum

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Advertisement

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.