Pos Fetal Screen + Neg Kleihauer-Betke?

[GilTphoto]

We had a mother come in to deliver her baby.

Her pre delivery Type and Screen was O neg (Du weak to 1+). DAT-neg, Antibody screen neg.

Her baby was O pos (Du 2+), DAT-neg

Her post partum Du was still weak to 1+, Fetal Screen 1+ both specimens.

So this indicates a large trans-placental hemorrhage.

Since we only get about 1 positive Fetal Screen every 10 years, so our plan was to send the Kleihauer-Betke to a neighbor hospital. They reported negative (no fetal cells seen).

Are these results conflicting? So how many vials of RhIG do I give? Since a positive Fetal Screen indicates more than 1.

I ordered the Simmler K/B kit shipped overnight and did the test myself. I also did not see any fetal cells, while the control worked fine (0.1 cord + 0.9 adult cells).

The AABB Technical Manual states that the K/B procedure's accuracy is poor, and any time the K/B is questionable, you can add 1 to the number of vials of RhIG to play it safe.

So to play it safe, we issued 2 vials.

Any thoughts or opinions?

Thanks, Gil

[Mabel Adams]

The fetal screen is positive because the mom has a weakly pos D antigen. The neg Kleihauer tells you that there really are not fetal cells present. The fetal screen measures D antigen, while the Kleihauer measures fetal hemoglobin. Determine the dose based on the Kleihauer. If you use the formula in the Tech Manual you will round down to zero and add one dose, which says to give the patient 1 dose. Two doses shouldn't hurt her.

Anyone that is recommending RhIG for weak D moms needs to have a policy addressing these cases so techs don't go nuts. Even if you give up doing weak D tests on moms, you still need the policy because you will find out they are weak D pos when you get a pos fetal screen and a neg Kleihauer.

[huntilla]

I would give two vials of Rh-Ig in this instance, but it would be interesting to see if the paternal sample was also a Du-pos. In that scenario, with the father being Du-pos, I think one vial would be sufficient to provide protection. It seems to me that the only way mom would mount an antibody repsonse is if the father was D-pos at immediate spin and even then it would be questionable. Were any of previous pregnancies on record for the mother in question, it would be interesting to know if she had previous Du-Pos infants.

Have a great week,

Barr Antilla, MT(ASCP), BB coordinator

[GilTphoto]

I was always under the impression that weak D's usually react 2+ or stronger at Du, that's why we classified the baby as Rh pos, but the mother's +/- result at Du only made me think of FMH.

Thanks for the replies.

Gil

[bbbirder]

I think that given the range of D-variants out there, you can get a whole variety of reaction strengths, some stronger than others. And the reagent you use will also affect the results you get. Some reagents pick up D-variants that others do not. We try to keep 2 types of Anti-D reagent on hand, plus the fetal screen anti-D gives us a 3rd

As Mabel said, there need to be policies in place so the techs don't go nuts. When we find a D-variant patient, we try to flag their BB history in the computer, so they get a little heads-up.

Linda Frederick

[AMcCord]

Weak D in AHG phase can be almost any strength. I've seen samples that test +/- and I've seen samples that test 2+. Remeber that there are several 'causes' for weak D. Your patient could have a low number of 'normal' antigen sites or could have a variant structure D antigen. The strength of reaction (or failure to react) can depend on which anti-D antisera you use.

If you check your package insert for the fetal screen, it will specify in limitations for the procedure that it must be performed only on the blood of a known D neg mother of a D pos child. If the mother is weak D positive, agglutination provides no info about how much feto-maternal hemorrhage has occured in these cases. The other thing to watch out for is that it also won't provide valid results if the baby is weak D positive. A negative test can occur with a large feto-maternal hemorrhage - those weak D baby cells may simply not be detected.

We flag our prenatals for weak D positive mothers with the comment that a Kleihauer-Betke is required. Saves confusion if the baby comes on the evening, night or holiday shift and there isn't anyone handy to ask about it.

There is one more thing to watch out for. If mom has a positive DAT, that will cause the fetalscreen to be positive. A Kleihauer-Betke is required for detection and quantitation of fetal cells in this case, too.

[GilTphoto]

This was the first time the mother came in, so we didn't know if it's a weak D or FMH. Mom's DAT was negative. We reported the mother as Rh neg. Should we now change to Rh pos(Weak D), now that we know the K/B had no fetal cells? Should weak D's be RhIG candidates? under what criteria? When the Du phase was 2+ or stronger we report Rh pos - not a candidate for RhIG. this seems to be a very gray area!

[AMcCord]

There have been some very lengthy discussions on what to call a patient - Rh pos or Rh neg - based on strength of reaction with anti-D on the AABB site and I think I've seen one on this site. The Technical Manual says it's a grey area for perinatal issues, so what us mere mortals are supposed to do.................?!?

A growing number of facilities choose to call any patient who types 2+ or greater MACROSCOPICALLY (or 3+ or greater in gel) as Rh pos and any patient who types as less than 2+ (or 3+) as Rh negative. Folks who are typed as Rh neg by these rules are given Rh neg blood and RhoGAM. The rationale is that without using molecular techniques, there is no way to know for sure who is going to be the patient with the right variation of weak D to form anti-D. Any positive result on a cord blood, no matter how weak, means mom is a candidate for RhoGAM. Again, without molecular techniques to determine what version of D baby has or even if that weak variant can truly stimulate production of anti-D, safe is better than sorry.

We are still wrestling with this subject.

You might check out what John Judd has to say on the subject, though right at this moment, I can't give you a specific reference. Mabel...can you help us out with that?

[Mabel Adams]

AABB published Guidelines for Perinatal Testing (or some similar wording) which is based on Judd's work and makes a very clearcut case for policies in this area. There also was an article by Judd in Transfusion several years ago that covered most of the same territory.

The only other point I would throw into the pot, and it is also not sure-fire, is that massive FMH could leave an anemic baby. Not always, as FMH can be more of a slow seep than a gush so the baby has time to make replacement red cells so is not anemic. So, if you get this picture with an anemic baby, you might feel the possibility is weighted toward FMH more.

[Mabel Adams]

There is one more thing to watch out for. If mom has a positive DAT, that will cause the fetalscreen to be positive. A Kleihauer-Betke is required for detection and quantitation of fetal cells in this case, too.

What might be the mechanism that makes a DAT interfere with the Fetal screen test? The indicator cells are coated with anti-D, not anti-IgG, right?

[AMcCord]

What might be the mechanism that makes a DAT interfere with the Fetal screen test? The indicator cells are coated with anti-D, not anti-IgG, right?

Good question! Makes me think on a Monday morning....... Mother's DAT may be due to an autoantibody which is capable of reacting with the indicator cells. If the auto does not have an anti-D specificity, it could have a more generalized specificity that could be reacting with the indicator cells. I wonder how common this problem would be? - not very high incidence at all, I would quess.

[rcurrie]

Mabel, the false positive FBS comes from crosslinking of the mother's antibody-coated cells, not due to a reaction with the indicator cells. It will look just like a rosette under the scope. You can use a sample of diluted mother's blood to help you tell the difference. It is a form of negative control, except you don't add anti-D or indicator cells, which could have the antigen to which the antibody is directed. If you see the same number of "rosettes" on the untreated patient sample, you probably have interference due to the positive DAT.

Happy New Year, everyone. I was engineer on the New Years Eve special last night, with about 200 revellers aboard. I have run the New Years Eve Special as engineer or conductor for the last 5 years. I learned quickly to mark up as engineer rather than conductor. Although I don't get all the good food that the conductor has access to, as engineer I don't have to deal with the over-indulgers.

BC

[jane eubanks]

So you give Rh immune globulin to Mom are telling her no quarantee you won't develop anti-D? I didn't know that the Rh immune globulin could only detect fetal cells.

[rcurrie]

Rh immune globulin is definitely no guarantee you won't develop anti-D, just as the flu vaccine is no guarantee you won't get the flu.

No one said that RHIG only detects fetal cells. It will attach to certain weak D cells as well. Although there are several theories as to how RHIG works, there is no evidence that any one of the theories is the only reason for prevention of immunization. I do not subscribe to any one theory.

BC

[jane eubanks]

I knew that Rh immune globulin could not tell the difference.(next time I will not try to be funny)

We do not give Rh immune globulin to weak D moms is it common practice to do so? It seems to me that the liablility is greater if you give the injection and they have a reaction I don't know what percentage of people react but anytime you give a human deriviative you run that risk.

[Mabel Adams]

I don't believe I have ever seen a reaction to IM RhIG, although I doubt allergic reactions would be reported to us. Anyone else have experience with this?

Since this practice of not doing weak D testing on pregnant women is becoming widespread, many of them must be getting RhIG. I guess if the reaction rate goes up, that will answer the question. It will take a long time to get any data on whether the D sensitization rate for them goes down, since it was so rare to begin with. As we've said elsewhere on these pages, most of us that have seen anti-D in an Rh pos person have seen in the patient that types 4+ with anti-D.

[yolis76]

Calling someone Rh neg who types 2+ with Anti-D must mean that your supplier is rich in Rh neg blood.....

Edited June 26, 2008 by yolis76
Missing a word

[rcurrie]

Well, I am now out of the blood bank business and running high speed passenger and freight trains for a living, but we collected our own blood, and we usually had about 100 O neg on the shelf and an additional 250-300 O pos. Not bad for a town of 55,000 people.

BC

[KKidd]

The Immucor fetal screen that I use states that if the infant is weak D positive, the screen is invalid and a KB stain must be performed. Check your product insert.

I even put a prompt in my computer to assist my techs. If a positive fetal screen is entered, the tech is asked if the infant is weak D positive. When they answer "Y" a reflex KB stain is ordered.

[SANDRA CORBETT]

Are you using the Imucor fetal Screen kit? It has a problem that the manufacturer has not disclosed to users yet. Note that 66% of the participants on the last CAP survey got the negative fetalscreen incorrect. They called it positive, and the fetal cell stain was negative. We have stopped using the kit and reverted to Kleihauer's in house with the Simmler kit until Immucor can resolve its problem. Negative tests are OK. There are no cases of false negatives I guess I will write a letter to CAP. I told them about it, Immucor is silent and studying the problem (they will acknowledge the problem over the phone), and Cap needs a letter to the Chair.

[Patty]

The fetal screen kit has Anti-D in it, it reacts with the baby's Rh pos cells yielding a pos result. If the Mom is Du pos, the fetal screen will be a false pos because it is reacting with Mom's cells. The fetal stain looks for fetal cells not Rh pos cells, so if should be accurate. I would present findings to our Pathologist and let the final decision as to the number of vials up to him, filling out a deviation report.

[KKidd]

The Immucor fetal screen insert states that an excessive bleed may not be detected if the infant is weak D positive.

[bbbirder]

Sandra,

I would not be so quick to assume that this is a problem with the test kit, or that it will carry over to patient testing.

We have had problems over the years with CAP immunology, chemistry, coagulation, and other surveys, often due to 'matrix' effects or other things that CAP can't explain. As a result, we have switched many of our surveys to API.

Linda Frederick

[AMcCord]

I'm also not ready to blame the kit. I had a different tech repeat the fetal screen with the Immucor kit after receiving the results of the survey. She stated that the 'rosettes' seemed atypical in appearance in the sample in question, more like loose aggregates than the tight rosettes we usually see and different in color. The positive control was normal in appearance, as was a sample we prepared by adding the cells of a newborn to an adult male. Based on the premise of better safe than sorry, she also would have reported the fetal screen as positive, with a KB to follow. We have never had a survey failure prior to this for fetal screens. I am more inclined to place the blame on the sample. It will be interesting to see what the followup is for this.

[kelliott]

If I understand you correctly the mother is weak D positive...on a predelivery sample. In that case you would expect the fetal screen test to be positive because the mother is weak D positive. The fetal screen reagent is an anti-D. You confirmed there were no fetal cells in the mothers sample with the KB test in the event the predelivery weak D test on the mother was in error. Unless using molecular testing to define whether the mother is weak D or partial D most are erroring on the side of safety as ou did and administering one vial of RhIG for a negative KB test.