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Positive DAT on Cord blood intefering with weak D test


John Bowers

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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+).

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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.

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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

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  • 4 weeks later...
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!

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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 by Abdulhameed Al-Attas
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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.

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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.

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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.

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