Du poitive patients;Rhogam

[Elizabeth Gillis]

We have many OB doctors who send there specimens to a reference lab, They claim they do Du part of there routine. We have had two different OB patients who upon arrival for delivery who Du is 2+, DAT negative. Doctor still insists the patients should receive Rhogam because they received it at 28 weeks. My pathologist caters to the doctors. Has anyone come across the same problem. Is it still ok to give Rhogam?

[Mabel Adams]

"We try to follow what the AABB "Guidelines for Prenatal and Perinatal Immunohematology" says... "Only when prenatal tests for Rh are unequivocal and clearly reactive (>/= 2+) should the woman be considered Rh-positive." Interestingly, John Judd, who put this together, said on the AABB member forum that he uses </= 3+ when using Gel anti-D testing.

Linda Frederick"

Above is a quote from one of the previous threads here on the topic. You could search for the others, or just get this AABB publication. It is very helpful in understanding current thinking.

It does not harm a weak D patient to get RhIG--and, if they turn out to be a partial D, we hope it helps prevent production of anti-D directed at the epitopes they lack. This is the motivation behind no longer doing weak D testing on anyone but donors and babies of Rh neg moms (i.e. sources of sensitization).

Of course there are partial D patients that type 4+ with modern reagents, so it isn't a very clear-cut area until molecular testing becomes standard.

[geekay]

Hi there,

In doubtful cases, giving Rhogam is safer than the complications arising out of "not giving it " !

It has been stated so in some standards manuals also ( I think Mollison ?)

best wishes..!

[Liz]

Dear Mabel,

With which reagents would weak D have a reaction strength of 4+ ?

Thanks

Liz:eek:

[ckcheng]

Since weak D test unable to distinguish between quantitative weak D and partial D, it is not required to perform weak D test routinely in transfusion hospital.

Perform weak D test in

(1) donor blood to conform true D negative, and

(2) baby of D negative mother. Cuz mother of weak D phenotype baby is candidate for RhIG and should evaluate for excessive FMH.

D negative mother (perform weak D is not required) should receive RhoGam injection at week 28.

Also, Standards for BB & Transfusion Services and Guidelines for Prenatal and Perinatal Immunohematology published by AABB are good references.

CK Cheng, MSc, SBB(ASCP), CQA(ASQ)

HONG KONG

Aug 6, 2008

[Liz]

On the gel technique, weak D gives a diffuse result, not a pure D negative. Has anyone had a clear cut negative result with the Du on the gel technology? Any references please? (we use Diamed).

I am also concerned about Mabel saying that they get 4+ with Du, what technique and how common is this? any references please?

Liz (worried)

[galvania]

Dear Liz,

Where are you working? Weak D come in many shapes and forms, and some 'strong' weak Ds will give a 4+ reaction with the various monoclonal anti-Ds in the cards. This isn't a problem as all of this type of weak D can be considered as D+ as both patient and donor. Most weak Ds will give a 1+ to 3+ reaction (a weak 3; a strong 3 is a normal positive). On the other hand, an extremely weak Dweak can be below the threshold of detection even for the gel. I have seen a couple of these - negative in direct tests, positive using the special anti-D formulated for use with the Coombs cards. Again, this is not a problem when testing patients, as these patients are better off treated as D-; could possibly be a problem for donors if thesey are in fact immunogenic. I know there have been a couple of papers claiming that even Del can be immunogenic, but i have no experience of this myself. As for partial Ds, they can also be extremely variable. Some partial Ds have almost normal quantities of antigen, even though the antigen is 'defective'. These partial Ds can also give a 4+ reaction with anti-D, if that particular monoclonal anti-D detects that particular variiant. One sub-type of DVI comes into this category; so does DIV. Depending on the reagent, they will also come up positive in direct tube testing. There may well be others. The typical way that these are detected is when an apparantly normal D+ presents with an anti-D. I had my first one of these about 35 years ago, shortly after I had just started as a trainee! It took quite a while to convince my boss that no, I hadn't made a mistake, and no, I wasn't going crazy. It turned out to be a 'strong' DVI. Of course at the time, all the antisera were human. And yes, this can be a problem for patients. It helps, of course, to use 2 anti-Ds, with different cell lines, with one not detecting DVI, but that does not, of course, eliminate all the problems. There is no technique in existence (apart from molecular testing) that would enable us to avoid every single one of these cases. Fortunately, they are very very rare..

[LaraT23]

We call all Weak D pos patients RH pos. So in theory that person is RH pos and would not be candidate for Rhogam. That being said, most weak D cases are due to a weak expression of the full D antigen either to position effect or an alteration in the protein. It may be prudent then, to confirm if this patient is infact weak or partial D, as with partial, she may make abs to the portion of the D ag that the baby has that she does not.

[NedB]

ckcheng and galvania have both succinctly stated our policy and procedure. Anyone calling a weak D Rh+ and not giving RhiG is taking a gamble. As it is with the strength of reagents in use now, we use a cut-off of > 2+ and don't do weak D except on donors and newborns.

[Mabel Adams]

I think Galvania covered this pretty well. Too bad our terminology and reagents don't really correlate with the biology. Weak D is a misnomer for a partial D that types 4+.

We have changed Du, weak D etc. terminology at least 3 times in the past 30 years; maybe we should make another try that fits the situations better--or should we wait for molecular testing to clarify things?

[galvania]

I agree with you there Mabel. I get a sneaky suspicion that we'll soon be going back to the situation of 30 years ago when everyone who wasn't D+ (4+) or D- was a Du (but now we'll call them D variants because thet's more 'scientific' ) and treated as a D+ donor and D- patient unless they've had a fully validated genotype done that proves that they are a D sub-type xyz and sufficient information is present to show that this particular genotype is/is not immunogenic/able to make anti-D. How many D subtypes are already known? Last count I think about 60 - but I'm probably out of date. I haven't looked for year or so...........

[madhu]

This is in reply to Liz's query if anyone has seen a clear cut negative in weak D on gel...yes, I have and I too use DiaMed gel. I have had many samples for weak D ranging between a weak to 1+/2+ on direct testing with anti-D and a 3 to 4+ with Du test on gel. One case was a clear cut negative with 2 different anti-D's on gel cards but a good strong 3+ on Du test using the AHG IgG card and the special anti-D for D weak testing.

[Liz]

Thank you Madhu,

what is the the special anti-D for D weak testing? what brand is it, Diamed?

Thanks,

Liz:)