Weak D testing

[Dawn]

What are the circumstances where you will perform weak D testing?

We currently have four situations in which we will perform weak D testing:

1. Cord blood or any other infant sample, particularly if the mother is Rh negative.

2. If the patient is the recipient of an Rh mismatched bone marrow transplant.

3. When the patient's Rh type appears not to match the historical type.

4. When the sample is from a donor.

Other than that we test for the D antigen at immediate spin only.

[adiescast]

We do a weak D on

1) Cord bloods when the mother is Rh negative.

2) The patient has autologous blood that is labelled Rh positive (we don't draw donors - if we did, obviously that would be another condition).

3) The patient develops Anti-D (like an antigen type).

4) An obstetrician requests ABO/Rh testing on male partners of Rh negative women with obstetric diagnoses.

[ChrisH]

We still weak D on all Rh negative patients.

[David Saikin]

I would like to upgrade to the latest AABB standards . . . this is being discussed by the Medical staff at this time.

[Jane]

I am also thinking about changing to the new standards but as I am pregnant myself this will be after my leave.

[GUY]

We do weak D testing on 1. All Rh neg women of child bearing age (11-55)

2. All Rh neg cord bloods (newborns) 8)

[John C. Staley]

Currently we weak D type all patients that test negative on immediate spin with anti: D. :shock: I am trying to change that so we are only testing weak D on babies when doing RhIG workups on their mothers.

[S.Hunt]

Currently we weak D type babies and Rh Negative mom's who have Rho(D) Positive babies and the FETALSCREEN TEST is extremely positive (i.e. 30 to 40 or more clusters per microscopic field.)

[catmontgomery]

We do weak D testing on babies who test negative on immediate spin with anti-D. We do not do routine weak D testing on mothers who test negative on immediate spin with anti-D.

[ANORRIS]

When performing a weak D, does anyone do a negative control? If so, what do you use?

[mel]

We use Affirmagen (reverse cells) for the negative control when doing QC on anti-D. Both cells are RH neg

[ANORRIS]

I mean a neg control with the patient's weak D, not the daily QC.

[mel]

We use the patient cells with two drops of saline for the patient D control. Blood banking has certainly come a long way with the arrival of monoclonal reagents. And automation!

[Yanxia]

I mean a neg control with the patient's weak D, not the daily QC.

We do the weak D use AHG mehod, we don't do the neg control . I don't know what kind of reason can give this test the false positive result .

Maybe you use the differ method as me, or I miss something to disturb this test?

[khalidm3]

We do the weak D use AHG mehod, we don't do the neg control . I don't know what kind of reason can give this test the false positive result .

Maybe you use the differ method as me, or I miss something to disturb this test?

It is necessary to perform Negative Control with Weak D test, to detect if patient cells are not already sensitized and if so our positive test result will be invalid, as these cells will agglutinate by AHG serum with or without Anti D

[khalidm3]

We use DiaMed Gel cards and they recommend using DCT as negative control. Some time ago we were using Auto Control as a Negative control with weak Rh but one of Inspector’s from Minister of Health arose this point that the DCT must be performed as negative control, not the Auto Control as recommended by the manufacture.

In my opinion DCT or Auto Control are mostly same, just it is simpler to dispense patient serum/ plasma in parallel to Anti D and read both test in comparison in one card. Now we perform weak D and DCT in separate or in single card.

With manual test tubes we use Rh Control in parallel with the Anti D.

[Malcolm Needs ☆]

We use DiaMed Gel cards and they recommend using DCT as negative control. Some time ago we were using Auto Control as a Negative control with weak Rh but one of Inspector’s from Minister of Health arose this point that the DCT must be performed as negative control, not the Auto Control as recommended by the manufacture.

In my opinion DCT or Auto Control are mostly same, just it is simpler to dispense patient serum/ plasma in parallel to Anti D and read both test in comparison in one card. Now we perform weak D and DCT in separate or in single card.

With manual test tubes we use Rh Control in parallel with the Anti D.

I can see from where the inspector is coming.

It is not an unusual situation in our laboratory to see a patient with auto-antibodies reacting only with enzyme-treated red cells (not by IAT, including the auto), but who has a positive DAT. This means that the auto control may well be negative, but that you are unable to "trust" any positive results seen in the weak D testing.

[khalidm3]

I can see from where the inspector is coming.

It is not an unusual situation in our laboratory to see a patient with auto-antibodies reacting only with enzyme-treated red cells (not by IAT, including the auto), but who has a positive DAT. This means that the auto control may well be negative, but that you are unable to "trust" any positive results seen in the weak D testing.

Can u explain me the phenomena "Positive DCT and Negative Auto Control or Positive Auto Control and Negative DCT" What cause this difference, When same cells are treated with AHG. The only difference is incubation in Vitro with serum/Plasma, Whereas patient cells and serum/plasma is already incubated always in Vivo?

[Malcolm Needs ☆]

The honest answer is "NO"; I wish I could!

It is just that we see this phenomenon quite frequently. Whether or not it is that the anti-IgG in the DAT card is stronger than the polyspecific AHG in our ordinary IAT cards I don't know, but that may be the answer.

[DANDERS]

What about if using the gel system? Is weak D testing necessary?

[Malcolm Needs ☆]

It doesn't depend upon the technique used, so much as the anti-D reagents. If the anti-D reagents are capable of detecting (most) cases of weak D, and are not capable of detecting Partial D VI (unless you use a special one for cords) then there is no need to perform further weak D testing.

If, of course, you do not have anti-D reagents that detect Partial D VI on cords, then they will not detect Partial D VI, even if you take them on the IAT. It is a pretty moot point as to whether Partial D VI on babies red cells have ever, convincingly, immunised the mother to make alloanti-D anyway (it depends on the view you take of the paper in which it was said to have occured).

[mel]

The gel system is great at detecting cells that formerly tested DU pos, but we still perform a DU on Rh neg moms and their babies. I can't remember an instance where the gel didn't detect the weak D.....my mind is quickly starting to lose stored data....but we still perform the test.

[khalidm3]

DiaMed provide Anti D VI+ and DVI- in their cards, We use DVI+ cards for new born, but still we test to detect weak or partial D by IAT using special Anti D which detects DVI and Weak Ds for our donors and neonates and some time we find a test positive by IAT, which was earlier negative with DVI detecting card. It is evident that is a Weak D

[cmelloh]

We only perform weak D on new patients who have no historical type.

[ckcheng]

Routinely perform weak D test on

(1) before labelling a unit of blood as Rh-negative, and

(2) cord blood sample if mom is a candidate of RhoGam injection.

Of couse when indicated in antibody workup.

Hope that helps.

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