Fetal Screen

[LaraT23]

Althougn I have no doubt you will all get this one, it really happened and we are a fairly small facility (125 beds) in a smallish town:

Mom - 23 year old involved in MVA, is 8 mos pregnant and is RH neg. We had no idea what the fetus was as far as type. We no longer do fetal stains and the tech here suggested a screen as a starting place. The screen was VERY positive. Thinking we had a severe bleed she called me at home and I suggested that she re-read the limitations before sending it for HgBF flow cytometry. She sent it anyway and it came back 0% fetal cells on flow. What do you think happened? The positive in the patient was repeated and was very positive.

Like I said easy, just surprised me.

[David Saikin]

Mom was weak D+; if you get macro results with the fetal screen that has to be the answer. The baby doesn't have enough blood to get that test macro positive.

Edited May 20, 2009 by David Saikin
added more info

[RR1]

I'm not going to spoil this...but I think it begins with ....H.

[David Saikin]

OK Lara - - - what is the answer?

[RR1]

Possibly Hereditary Persistance of Fetal Hb (HPFH) ?

[rescyth]

hmmmm....

0% fetal cells

==> no fetal cells to begin with

==> mom is a high titered O and baby is ABO incompatible(test was done on a redrawn sample)

The positive in the patient was repeated and was very positive(no technical error)

==> test was performed in primary tube (both initial and confirmatory)

3rd option...

weak D

[RR1]

Slightly raised HbF levels can give a positive Kleihauer picture, but this would not necessarily be significant enough to be detected by flow cytometry......of course-I could be writing a load of rubbish!!

[Vaatha]

The majority of our patients are OB's. We have seen enough cases where the fetal screen is overwhelmingly positive due to the patient actually being Weak D positive that we actually have as our policy that the tech must do a weak D workup if the fetal screen is positive, before turning out any positive fetal screens. If the weak D is positive, then we turn the fetal screen out as indeterminate. Either way, we would still order a Kleihauer-Betke to determine hemorrhage and dosage. Despite the weak D, we would still consider these patients as Rh negative in regards to receiving any blood products or rhogam injections.

[LaraT23]

That little missing part of the D ad sure does give us problems. I did a weak D on the mom the next day and bingo, pos. I had asked my night tech to do a weak D before sending it out as positive but she didn't. I added a line in the computer that requires the weak D be resulted before finalizing the report. I am also going to require that the specimen be recollected before we result a positive screen. So many of my techs seem to "see" things and when I retest a new sample, there is nothing. The Flow lab must think we are all bonkers!!

[RR1]

Hi everyone.....I think I need a bit of educating here! When you talk about a screening test- are you therefore referring to the Rosette Test?

We only use the Kleihauer test for screening our patients, though there may besome labs in the UK using Rosette. As you probably know, some patients with haemoglobinopathies/ HPFH can show a positive K-B stain either as a pancellular or heterocellular picture, which can make determining FMHs difficult.

[Malcolm Needs ☆]

Are we talking weak D or partial D here?

If it's a weak D, then why on Earth are you giving anti-D immunoglobulin prophylaxis Vaatha?

If it's a weak D, what part of the D antigen is missing LaraT23?

I am well aware that there have been reported cases of weak D Type 1 and 2 individuals making very weak alloanti-D, but they are extremely few and far between.

This is another occasion where I think Geoff Daniels, Joyce Poole and Geoff Poole are absolutely correct in writing that partial D and weak D (and DEL, come to that) should all be regarded as variant D.

All that having been said, I think it was an excellent case study!

HbF indeed RR1!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Edited May 27, 2009 by Malcolm Needs
Forgot something very important!

[Vaatha]

To complicate matters, there is also the slight problem of false positives occurring with the Immucor Fetal Bleed Screen Kit. We had quite a problem with that for several months, and were driving our hematology dept crazy with all the Kleihauer-Betke orders due to the false positives. After a recommendation from one of the Immucor technical staff, we switched to using buffered saline in our FBS procedure, and that seemed to solve our problems. We did a small correlation to make sure the buffered saline was getting accurate results, which it was. We haven't switched back to regular normal saline and we don't plan to-not while it seems to be working okay that way.

[RR1]

Purely a misunderstanding of the word 'screen'- which I took to mean a K-B test. I have never performed a Rosette test, which is I presume what we are talking about. Is this still a commonly performed test then ?

[Mary**]

Yes, the rosette test isused for the routine screening of post-partum mothers.

[RR1]

Hi Mary,

Wouldn't it be easier just to perform the K-B test on post-partums? ( I just need educating on this !)

Thanks

[L106]

The K-B test is much more labor-intensive. The FMH (ie: Rosette test) can be more easily performed along with (or in-between) other regular Blood Bank benchwork.

[Brenda K Hutson]

Right, not much help doing a Fetal Screen if you don't have the ability to do a KB. Without knowing the baby's Rh Type, if the screen is Positive, what are you going to do? It would need a KB anyway. And if the Screen is Negative, is it because the Baby is Rh Negative, or because there was not a large bleed? Also, you mentioned that it was strongly positive. Just wondering if you carry your Rh testing through to Weak D on pregnant women? We do not; so if I get a positive Fetal Screen, especially if macroscopic, the first thing I do is Weak D testing on the Mom. Though I did have one once that I still cannot explain; macroscopic positive Fetal Screen, Mom is Rh, Weak D Negative, KB Negative???

Brenda Hutson, CLS(ASCP)SBB

[LaraT23]

Malcom: don't know, maybe have a weak D, maybe a partial. Rosette tests of course include a chemically modified anti-D reagent. This will attract both baby ( if RH pos, neg mom) and the mom ( if rh pos, even weak D.). Our ED doc insisted on having this done even though we had no idea the RH of the baby. He as just looking to find a way to indicate a fetal bleed or not. I have since told the ED that the rosette test is not going to be effective really in that case. We will send all non-delivered mom's samples for Flow cytometry. We don't do KB stains.

I have explained the pitfalls of this test with my staff. It isn't fool proof, there are a few things that can cause a false pos ( including pH of the saline apparently). We do not routinely do the weak D on our delivering moms unless they have an RH pos infant and we are going to do a fetal screen. It is a really all about understanding what we are looking for and how the test works. Knowing those things, we can decide whether what you are seeing is a real pos or has potential to be false!

[RR1]

The K-B doesn't take that long to stain and look at films, especially if you consider the time spent in reflex testing your Rosette test, weak-D typing, ensuring you have covered all aspects of the reason for the positive Rosette, and then having to eventually perform a K-B anyway.

Try mapping your current process to see if it would be leaner to just go over to a K-B test.

[LaraT23]

We did take a look at that and with the cost of the CAP survey and the cost of reagent and the number we would do a year ( like maybe 3) it just doesn't make sense. This is not to mention the competencies. My night techs almost passed out when we talked about doing those again. We only have 3 techs on nights for the entire lab, and they might mutinize if I asked them to do KB's again!