Passive Anti-D in Capture-R Ready method

[Diane Lowitz]

We are in the process of validating the Capture-R Ready method (solid phase) with the intent of switching from Gel to the ECHO. I just discovered that passive anti-D is not detected in the Capture-R method. I am concerned that this passive anti D is not being picked up. We are a pediatric center and have always honored a passive anti-D when transfusing neonates. With Capture-R Ready method we will not be aware of a passive anti D and will transfuse RH positive red blood cells. This bothers me and I am not sure if this will affect the babies outcome. How do other facilities handle this or is this not an issue? Thanks in advance for any help.

[John C. Staley]

This is odd. One of the reasons we stopped doing antibody screens on post partum RhIG workups for patients with a negative antibody screen during their antenatal workup was because we were constantly going through the process of identifying the passive anti-D we picked up with the echo as a result of the 28 week antenatal RhIG injection. Please explain your process which led you to the conclusion that the Capture R does not detect passive anti-D.

[Malcolm Needs ☆]

This is odd. One of the reasons we stopped doing antibody screens on post partum RhIG workups for patients with a negative antibody screen during their antenatal workup was because we were constantly going through the process of identifying the passive anti-D we picked up with the echo as a result of the 28 week antenatal RhIG injection. Please explain your process which led you to the conclusion that the Capture R does not detect passive anti-D.

I'm pretty amazed by this too John.

[Diane Lowitz]

It is stated in the Manufacture Insert as a limitation to the procedure. It states "Some IgG antibodies have shown to react poorly in solid phase red blood cell adherence assays. ...Passively administered antibodies may fail to react by Capture-R Ready Screen, even though the antibodies are detected by alternative technique." I also ran a screen plus panel using this methodology and it failed to detect the passive Anti-D.

[Malcolm Needs ☆]

That's a worry Diane, because 1) alloanti-D starts out as IgM, but quickly changes to a weakly reacting IgG and, 2) what other IgG specificities does it miss?????????

[Diane Lowitz]

According to the package insert it states Bga, Bgb, Kna, Csa, Yka, JMH, McCa, Ch and Rg. My main concern is if a passive D is not honored in a transfusion to a neonate which is a premie will this cause any harm to the neonate who is rh positive? We do not have a maternity center at the hospital and rely on babies transferred to us for treatment. We do not see mom's specimen or have a history on mom to know if she received Rhogam . It is our policy to give type specific blood whenever possible. We preserve our Oneg blood for those who really need it.

[Malcolm Needs ☆]

Well, from that point-of-view, I doubt if the passive anti-D will cause too many problems, and I wouldn't worry two hoots about not detecting antibodies of those specificities (in fact, I wish we didn't!!!!!!!!!).

If you think about it, there are an incredible number of D Positive babies that have been born to D Negative Mums, where the Mum has received prophylactic anti-D immunoglobulin (sometimes in quite large doses) where the baby has not suffered any clinically significant sequalae, even though their own D Positive red cells are sensitised by the passive anti-D. Most of this passive anti-D will have been "mopped up" by their own D Positive red cells, and so there will be very little passive anti-D left to cause any problems if donor D Positive red cells are transfused to the baby. This, of course, is quite a different situation to where the mother has produced a cracking alloanti-D of her own, where there certainly would be clinically significant sequalae, should D Positive donor blood be transfused to the baby.

[R1R2]

Well, from that point-of-view, I doubt if the passive anti-D will cause too many problems, and I wouldn't worry two hoots about not detecting antibodies of those specificities (in fact, I wish we didn't!!!!!!!!!).

If you think about it, there are an incredible number of D Positive babies that have been born to D Negative Mums, where the Mum has received prophylactic anti-D immunoglobulin (sometimes in quite large doses) where the baby has not suffered any clinically significant sequalae, even though their own D Positive red cells are sensitised by the passive anti-D. Most of this passive anti-D will have been "mopped up" by their own D Positive red cells, and so there will be very little passive anti-D left to cause any problems if donor D Positive red cells are transfused to the baby. This, of course, is quite a different situation to where the mother has produced a cracking alloanti-D of her own, where there certainly would be clinically significant sequalae, should D Positive donor blood be transfused to the baby.

I agree with Malcolm. In fact, I don't think I have ever seen an Rh positive baby with passive anti-D in plasma (DAT positive only).

R1R2

[Malcolm Needs ☆]

Ah, sorry R1R2, that wasn't quite what I said.

The key word in the post (as far as that bit was concerned) is "most". We do detect passive anti-D immunoglobulin in the plasma of some babies, albeit, it is very weakly detected by IAT (stronger with enzyme-treated red cells - but then, you would expect that).

[AMcCord]

We don't have any trouble detecting RhoGAM in the mother's sample using the Echo, unfortunately - much more so than gel. I can't say that we've seen it in infant samples, though we do antibody screens on very few, so I can't really make a statement one way or the other.

[John C. Staley]

It is stated in the Manufacture Insert as a limitation to the procedure. It states "Some IgG antibodies have shown to react poorly in solid phase red blood cell adherence assays. ...Passively administered antibodies may fail to react by Capture-R Ready Screen, even though the antibodies are detected by alternative technique." I also ran a screen plus panel using this methodology and it failed to detect the passive Anti-D.

I see this as the CYA statement you find just about anywhere. I find the use of the words "some" and "may" to be what I fondly refer to as waffle words. Now if they used "most" and "will", that's an entirely different cup of tea. As Malcolm noted, in the real world you probably (my favorite waffle word) have nothing to worry about.

[Malcolm Needs ☆]

As Malcolm noted, in the real world you probably (my favorite waffle word) have nothing to worry about.

I've got a PhD in waffle John!!!!!!!!!!!!!!!!!!!!!!!!

:bow::bow::haha::haha:

[marvy1]

We don't have any trouble detecting RhoGAM in the mother's sample using the Echo, unfortunately - much more so than gel. I can't say that we've seen it in infant samples, though we do antibody screens on very few, so I can't really make a statement one way or the other.

We also find that Rhogam and allo-D antibodies both show up stronger in Echo than in Gel

[David]

Ditto to AMcCord. Our detection rate for passive D's has increased 10 fold since we switched to the Echos.

[BldBnker4]

I see this as the CYA statement you find just about anywhere. I find the use of the words "some" and "may" to be what I fondly refer to as waffle words. Now if they used "most" and "will", that's an entirely different cup of tea. As Malcolm noted, in the real world you probably (my favorite waffle word) have nothing to worry about.

We are constantly detecting passive Anti-D's in our OB patients with our Echo. It made validation challenging when our bench (manual) screens were negative and the Echo was finding the prenatal Thogam Anti-D's! I can't imagine why you are not detecting the passive Anti-D's? We have also been detecting weak Anti-Jka and Anti-Jkb antibodies too. Manual screens are negative. We are seeing these in recently transfused patients....maybe newly formed "baby" antibodies?!