Is anyone calculating FMH by Kleihauer-Betke when the mother is RhD neg and infant is weak D? Since with regular testing we cannot determine if infant is weak or partial D we treat all those tested as weak D as if they could cause immunization. However in package insert for Fetalscreen test (using rosette method) it says that the screen may be falsely negative if the infant is weak D. Should we then require that a Kleihauer test be done in these cases? Of course we all hate the K-B in our chronically understaffed BB. Could the weak D infant cause the mother to need more than one vial of Rhogam even with a bleed of more than 30 mL?

Is anyone calculating FMH by Kleihauer-Betke when the mother is RhD neg and infant is weak D? Since with regular testing we cannot determine if infant is weak or partial D we treat all those tested as weak D as if they could cause immunization. However in package insert for Fetalscreen test (using rosette method) it says that the screen may be falsely negative if the infant is weak D. Should we then require that a Kleihauer test be done in these cases? Of course we all hate the K-B in our chronically understaffed BB. Could the weak D infant cause the mother to need more than one vial of Rhogam even with a bleed of more than 30 mL?

Yes; a weak D infant could cause an Rh-Neg mother to produce of an allo- D in the mother with a significant fetal/ maternal hemorage. And, Yes, a KHB should be performed in order to determine the number of RhoGam vials to be administered. Ultimately, we strive to circumvent the production of an allo-D in the mother such that future pregnacnies will not be jepardized. We utilize the FMH screen as a qualitative precursor to performing the KHB, which is quantitative. In other words, if the FMH screen is negative then no KHB is needed and one vial of RhoGam is administered; if the FMH screen is positive then we proceed with the KHB and calculate the number of vials of RhoGam to be administered. An Rh-Neg mother's immune system can recognize a weak D, do to decreased expression or protein alteration, as being foreighn and therefore produce an allo-D. You must remember that the FMH detects fetal cells via presence of D Ag where the KHB detects fetal cells through staining fetal Hgb.

Hope this helps. :)

Yes, we perform KB testing in place of the rosette test if the baby is weak D and the mother is Rh neg. And I agree with you - I really dislike the KB test! Belva in Lincoln

Yes; a weak D infant could cause an Rh-Neg mother to produce of an allo- D in the mother with a significant fetal/ maternal hemorage. And, Yes, a KHB should be performed in order to determine the number of RhoGam vials to be administered. Ultimately, we strive to circumvent the production of an allo-D in the mother such that future pregnacnies will not be jepardized. We utilize the FMH screen as a qualitative precursor to performing the KHB, which is quantitative. In other words, if the FMH screen is negative then no KHB is needed and one vial of RhoGam is administered; if the FMH screen is positive then we proceed with the KHB and calculate the number of vials of RhoGam to be administered. An Rh-Neg mother's immune system can recognize a weak D, do to decreased expression or protein alteration, as being foreighn and therefore produce an allo-D. You must remember that the FMH detects fetal cells via presence of D Ag where the KHB detects fetal cells through staining fetal Hgb.

Hope this helps. :)

Are you saying you do not do the K-B if the FMH screen is negative? According to the screen package insert it says that with a weak D infant the screen may not be positive even with a greater that 30ml. bleed. We are currently not following a negative screen with a K-B, although I am not sure how many if any infants we have had in these cases that are weak D since we report these babies out as RhD positive.

I think we have to be really careful with Weak D phenotypes. Although very rare, alloanti-D has, as someone else pointed out in another thread (sorry, I can't remember either the thread or the poster) been detected in individuals with Weak D Types 1, 2 and 3, amongst others (such as 4 and 15).

However, a Weak D Type 3 foetus has also been recorded as stimulating anti-D in the mum (Needs M, Poole J, Tilley L, Stern S, Preddy I, Win N. Stimulation of anti-D in pregnancy by a Weak D Type 3 foetus. Transfusion Medicine 2007; 17 (suppl 1): 40 (P17) Abstract.), and so I think that, under the circumstances described, the KHB test may be better than FMH.

:confused:

I must agree with Malcolm on this issue. As rravkin pointed out the FMH screen is reliant upon the D antigen to give a positive result. The KB would be a safer choice to avoid potentially "missing" a larger bleed requiring more doses of RhIg.

Malcolm I think the weak D types were mentioned in the post where stoogiesfreak posed a question related to the end stage lung cancer patient "changing" from A negative to A positive.

Are you saying you do not do the K-B if the FMH screen is negative? According to the screen package insert it says that with a weak D infant the screen may not be positive even with a greater that 30ml. bleed. We are currently not following a negative screen with a K-B, although I am not sure how many if any infants we have had in these cases that are weak D since we report these babies out as RhD positive.

Hey Jane,

You are correct! This case does require KHB reguardless of the FMH. As such, and in retrospect, I would think that the FMH might not be necessary.:)

We would send it for flow--much less subjective than KHB.

Is anyone calculating FMH by Kleihauer-Betke when the mother is RhD neg and infant is weak D? Since with regular testing we cannot determine if infant is weak or partial D we treat all those tested as weak D as if they could cause immunization. However in package insert for Fetalscreen test (using rosette method) it says that the screen may be falsely negative if the infant is weak D. Should we then require that a Kleihauer test be done in these cases? Of course we all hate the K-B in our chronically understaffed BB. Could the weak D infant cause the mother to need more than one vial of Rhogam even with a bleed of more than 30 mL?

We will perform Weak D testing on the baby's cord sample if the immediate spin D typing is negative or very weak. If the baby is weak D test posiitve, we will interpret the baby is Rh Positive and perform BK test for the Rh neg mother and skip the fetal screen test.

Does anyone have a reference on this?

The package insert for fetal bleed screens has a list of references. Can you ask your hospital library or education department to acquire those articles for you?