New Thought on Weak D testing

[Mary**]

Yesterday we had a post-partum specimen for a Rhogam workup including FMH screening. The screen was 2+ macroscopically. We had no previous history and had not done any weak D testing on her, which is our protocol. Her prenatal specimen was sent to a commerical lab that most likely does not do weak D testing on D Negatives.

We performed weak D testing and it was positive which invalidated the FMH screen. A Kleihaur Betke stain was negative. The physician wanted to give the Rhogam to her, which we did.

When you have no history, as in this case, a situation like this in the hands of an inexperienced tech could have been misinterpreted as a VERY positive FMH screen which would have been resolved by the negative KB Stain, but would have left the tech who didn't consider that the patient might be a weak D confused.

[Malcolm Needs ☆]

Yesterday we had a post-partum specimen for a Rhogam workup including FMH screening. The screen was 2+ macroscopically. We had no previous history and had not done any weak D testing on her, which is our protocol. Her prenatal specimen was sent to a commerical lab that most likely does not do weak D testing on D Negatives.

We performed weak D testing and it was positive which invalidated the FMH screen. A Kleihaur Betke stain was negative. The physician wanted to give the Rhogam to her, which we did.

When you have no history, as in this case, a situation like this in the hands of an inexperienced tech could have been misinterpreted as a VERY positive FMH screen which would have been resolved by the negative KB Stain, but would have left the tech who didn't consider that the patient might be a weak D confused.

I agree that it would Mary, but there are ways around it that, perhaps, should be added to the standard SOP.

I presume, by FMH screening, you are using an anti-D to see mixed-field/rosetting? If you are getting such strong results (and these are true results) it is a fair bet that the baby would be anaemic. It might be worthwhile writing a step into the SOP saying that the baby's Hb should be estimated. If this is normal, or near normal, it may be a guide that other tests need to be performed.

In such a case, a KB would, of course help, but if this is also positive (because there has actually been a slight FMH, or because the mother has elevated HbF), then testing by FITC conjugated anti-D with flow cytometery may help. This would give an enormously positive result (if the mum is a weak D [and, in many cases, but not all of course, if the mum is a partial D]). This result will be at odds with the slightly positive KB result if there has been a slight (or no) FMH (although it will not help in the case of the mother having a high HbF level). In this case (the high maternal HbF) using a conjugated anti-HbF may help (but this method has not, as far as I know, been fully validated anywhere).

Having re-read this post, I not sure that it will help, or muddy the waters even further (but it is an attempt to help)!

:confused:

[Mary**]

:whew:The baby was not anemic and fortunately the KB was negative. It would have been more complicated if either had been so. Thanks for your thoughts Malcolm.

[LaraT23]

I require that before anyone here reports out a positive rosette, the mother has a weak D test done. If negative, we send the specimen out for flow cytometry. If positive, we report invalid rosette and request that the physician notify the lab if he wants flow done for fetal cells. Sometimes they just give an extra vial and call it a day if they are sure there was no trauma during delivery. Most of them do want the specimen sent for flow though...just for CYA.