Serologically possible?

[labgirl153]

Gang, am creating some flowcharts for a small lab that was inconsistent on their D typing and weak D SOP (for neonates and preg. women with + fetalscreens). Was asked to include all serologic reactions/possibilities that could occur with weak D typing; however, they wanted me to include the reaction of weak D negative, DAT positive.

To be honest, I've never seen this reaction in all my years and wonder if it's even serologically possible. After all, if the patient's cells are coated with IgG (allo or auto in derivation), then shouldn't the weak D also be reactive at AHG - and thereby the test is invalid? BTW, this lab uses tube method and the DAT is the control for weak D testing. Dumb question but thought I'd run it by you all.

[Rh-fan]

When you use a indirect antiglobulin test for your weak D testing, it can not be negative when your DAT is positive. Only when your DAT is very weak, on the edge of detecting, maybe the weak D test can be negative but this is a very smal change

[labgirl153]

Thx Rh-fan. Didn't think I was crazy but thought I'd better run it by just to get some affirmation from other blood bankers :cool: Been awhile since I worked in a real blood bank and the generalist crowd sometimes gang up and insist that something like this is possible when in fact it's not.

[Malcolm Needs ☆]

I agree with Rh-fan.

You could buy some IgM anti-D reagents that work with DAT+ red cells (i.e. they will give negative reactions with D-, DAT+ red cells, and positive reactions with D+weak, DAT+ red cells, but they cost a fortune, and the number of times you will require them would mean that they may well expire before you have even used them once.

[galvania]

Malcolm - do you mean IgM anti-D reagents that work by IAT?? Otherwisw, most monoclonal anti-D reagents that I know of are IgM and would not give you a false positive reaction due to a pos DAT. I'm confused. I think maybe my brain isn't working very well today.......

[Malcolm Needs ☆]

No, I meant IgM anti-D reagents that work by straightforward agglutination - sorry if I didn't make myself clear (NOT the first time in my life!).

I was thinking of such reagents as TOTEM (can't for the life of me think who makes it off the top of my head), but it's like superglue for weak and some partial D's. If a red cell has seen a photograph of a D antigen, it will agglutinate it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Well almost - but it is a very good reagent.

[Rh-fan]

Labgirl,

What is the reason that you do a weak D test (patient, donor or cord blood) ?

The monoclonal anti D reagent from Immucor/Gamma (rapid) contains the Monoclonal antibody RUM-1. This is one of the most sensitive IgM anti D antibodies, it is reactive (at RT) with weak D type 2 (one of the most commen weak forms of D antigens). Some publications (W. Flegel) have stated that a type 2 weak D antigen should be detectable with your reagent to say it is sensitive enough.

In a hospital setting it is not nessecery to detect weak D antigens in patients, in cord blood the above mentioned MoAb will detect almost all forms of weak D antigens.

[crldehart]

Gang, am creating some flowcharts for a small lab that was inconsistent on their D typing and weak D SOP (for neonates and preg. women with + fetalscreens). Was asked to include all serologic reactions/possibilities that could occur with weak D typing; however, they wanted me to include the reaction of weak D negative, DAT positive.

To be honest, I've never seen this reaction in all my years and wonder if it's even serologically possible. After all, if the patient's cells are coated with IgG (allo or auto in derivation), then shouldn't the weak D also be reactive at AHG - and thereby the test is invalid? BTW, this lab uses tube method and the DAT is the control for weak D testing. Dumb question but thought I'd run it by you all.

We have seen this happen in the days of tube testing and "dirty" cord blood collection (stripping the cord vein into a tube). There was so much wharton's jelly in the sample that 4-6 washes were required prior to DAT testing. If the DAT was weakly positive, the additional washes after incubation in the weak D test seemed to remove the cause of the positive DAT and left us with a negative weak D test. This is not a problem now, cleaner collected samples and Gel technology.:)

[jeanne.wall]

I actually have seen this (D negative at IAT, D control negative at IAT, in a patient with a weak positive DAT) happen once in my almost 40 years' experience. My theory was that the antibody coating the red cells actually eluted off during the incubation phase and in fact I could actually demonstrate the antibody in the supernatant of the tests collected prior to washing. I think it is a fluke, all stars aligned, the moon in the right phase, and I must have twitched my noise correctly as well, but it was reproducible. I will also accept Malcolm and the rest of you telling me I’m crazy – I couldn’t have seen it.

If I were you, Labgirl, I wouldn’t include it in a chart like the one you are creating. Understanding when something really odd happens is part of the fun of Blood Banking and that is the fun of Blood Banking that those odd things do happen once in a lifetime. Our responsibility is to understand they do happen, but may not happen again and shouldn’t become part of every decision we make.

Jeanne Wall, M.Ed., MT (ASCP) SBB

[labgirl153]

Thx for weighing in all...gave a brief presentation yesterday to the crew and posted flowcharts. I did qualify my talk with the disclaimer of: "some of what's on the flowchart is a rarity so tuck it away". The flowcharts are guidelines - not SOPs - and they are very clear. Most of the scenarios I gave were to dissuade the crew from doing weak Ds on adults (some were running weak D with no DAT and wrongly reporting out adults as weak D +). I'm new at the facility and the crew there is an older crowd who have virtually no guidance. In other words they've been "making up" their own protocols (a no-no).

Having said that, according to the fetalscreen inserts, if Pos, it's wise to perform a weak D on the mother and also a DAT to discover the source of that positive. Regardless, a K-B needs to be done. In addition, we do perform weak Ds on all Rh negative cords and if the weak D is + with a positive DAT, we report it out as "Rh indeterminate". The M.D. is advised to retest the child later (3 mo. or so later). We then perform a rhogam work-up on mom, under the assumption that the infant is D+. We then leave it up to the M.D. as to whether he/she wants to administer RHiG. I've seen this SOP many times at other facilities great and small over the years.

Also, I'd love to get them on-board with gel (a fav of mine), or solid phase, but there are some private obstacles to that right now. For now, it's tube only.

[Malcolm Needs ☆]

The M.D. is advised to retest the child later (3 mo. or so later).

Ummmmm, why?

Whereas antigens that are not direct gene products (but the result of the action of transferase enzymes), such as ABO, Lewis, etc definitely do change with age, antigens that are a direct gene product (apart from a bit of post-translational "editing"), such Rh will not, so why retest later???????????

Please ask him/her, because I am always ready to learn.

Edited September 21, 2011 by Malcolm Needs
Spelling (yet again).

[labgirl153]

Malcolm, I mean...where the cord blood DAT is positive and weak D is +...maternal IgG coating the infant's erythrocytes diallowing us to confirm that the infant is indeed D= until those coated cells are taken out of the system. Hope that clarifies it.

[Malcolm Needs ☆]

Ah, right. Sorry I mis-interpreted what you were saying.