How do other facilities manage RHIG administration when the test for Weak D on cord blood is likely falsely positive due to ABO incompatability induced positive DAT. In this case the RH status can not be reliably determined, but most likely is Rh negative as the reaction strength is equal to the DAT (w+).

If need be perform K/B testing to determine the number of RHIG vials needed.

I agree. We perform K/B testing in the case of a "true" weak D positive cord blood because on the possibility of getting a falsely negative Fetal bleed screen and to determine dosage. But one might argue no Rhogam is necessary as the baby is probably Rh negative. I think the decision to give RHIG would vary among different OB/GYN's.

Does anyone try to remove bound antibody to get an accurate D type?

R1R2

We have a heelstick specimen drawn on the baby and type the baby. Usually the DAT is negative on the heelstick and we get an accurate D type.

We use IgM monoclonal anti-D reagents, so the DAT does not interfere with the results.

I have always used a mild heat elution (56C) with 8% albumin to remove the weak ab. Works great but is a bit time consuming. We don't have to use it that often.

You could try chloroquine diphosphate, but, that having been said, I doubt whether you would carry this as part of your reagents, because you wouldn't have to use it that often.

We do have it, but even we, as a Reference Laboratory, rarely use it.

the ability to remove the bound antibody is dependent on the strength of the DAT, also. None of the gentle elution methods work with a strongly positive DAT. Surprisingly, we have access to chloroquin and not the IgM anti-D. We do the K-B stain and give RhIg just in case.

How do other facilities manage RHIG administration when the test for Weak D on cord blood is likely falsely positive due to ABO incompatability induced positive DAT. In this case the RH status can not be reliably determined, but most likely is Rh negative as the reaction strength is equal to the DAT (w+).

The Rh interpretation should be reported out as Rh inconclusive and your Fetal Screen kit should say it is not accurate if weak D+ in Mom or Baby, so do a Kleihauer betke to calculate RHIG, this mother needs RHIG. you can't assume baby is Rh neg

How do other facilities manage RHIG administration when the test for Weak D on cord blood is likely falsely positive due to ABO incompatability induced positive DAT. In this case the RH status can not be reliably determined, but most likely is Rh negative as the reaction strength is equal to the DAT (w+).

Have you thought about using the fetal screen kit directly on the baby's specimen not the mom? On priniciple, the kit detects D+ cells regardless where they are at. the Positive DAT does not interfere with testing (by the testing our facility performed) You might think about using this principle in conjunction with the degree of positive DAT in the baby. I have read of others doing this. We use Immucor fetal screen kit and currently trying to get more info on this use of the kit. Just a thought!

Very interesting... thanks for that info.

We consider the baby Rh neg Weak D unable to determine and do a FTLS and give Rhogam. Better safe than sorry.

Landsteiner Heat (56°C): is NOTsuitable if the purpose is to elute antibody and save the red cells for antigen typing or for autoadsorption. The heat elution at 56°C denatures antigens.This method is mainly useful for cold antibodies or antibodies that react in both the cold and the warm, e.g., antibodies that cause ABO-HDN. It does not recover warm antibodies as well as the other methods but is relatively simple and rapid.
The Modified Heat Elution( 40°C- 45°C):
Unlike the regular heat elution at 56°C, the modified heat method uses lower temperatures that will not denature antigens. A disadvantage is that the DAT may not become negative until the temperature is so high that antigens may be denatured.

Edited August 27, 201410 yr by Abdulhameed Al-Attas

What is a FTLS (not familiar with that acronym). Fetal Bleed screen? I would think a Fetal Bleed Screen would give you a false negative given that it is not labeled to be used as a screening test for weak D infants. Rather a Kleihauer-Betke should be done instead.

We also report the baby's blood type as indeterminate and give RhoGAM to be safe (Kleihauer-Betke is done). We tell the pediatricians that we can give them an accurate Rh type on baby in a few months, if they'd like to send the tot in to be redrawn and retested, but so far we've never seen one.

We also report the baby's blood type as indeterminate and give RhoGAM to be safe (Kleihauer-Betke is done). We tell the pediatricians that we can give them an accurate Rh type on baby in a few months, if they'd like to send the tot in to be redrawn and retested, but so far we've never seen one.

We do the same.

I agree with profbaud

I am just curious as to how most people are doing the cord DAT - tube or gel?

I am just curious as to how most people are doing the cord DAT - tube or gel?

We run Cord Blood samples on the Provue. Gel is our backup if the Provue is down.