Fetal Bleed Screen - false positive's

[kelliott]

How many of you have seen an increase in the number of false positives beginning the last 8 months or so?

We have been frustrated with this and the slow immucor response to resolve this problem.

We opened a new lot two weeks ago. The first 7 patients had positive fetal screen tests and no fetal cells seen on the fetal stain.

We have tried all that the manufacture has suggested: extra washes, buffered saline, alternate blood collection tubes.

We have made no changes since implementing this kit 3-5 years ago.

Immucor has relocated the manufacture of the kit and it was around that time we started noticing false positives.

Yesterday during a student training session, a D neg male sample was selected to ensure we would obtain a negative FS test...it was positive.

Has anyone found a solution for this very frustrating problem?

It will be awhile before Ortho has a kit available...but they are working on one.

[lef5501]

We haven't seen too many false positives recently. We had quite a few in the past though. Our biggest concern at the moment is that the positive control is not positive. It's just as negative as the negative control.

[KKidd]

I have only had one positive fetal screen that had any fetal cells when the KB stain was performed. We are also getting a weak positive control with the current lot.

[cooltech]

Glad I'm not the only one having issues with the current lot's weak positive control...

[Eagle Eye]

we had several patient with positive fetal screen and no fetal cells in KB.

[bxcall1]

I agree that about 8 months ago the only fetalscreening kit available went down the toilet. We have had alot of 'positive' fetalscreens with negative KB's.

I wish there was some competition for this product, then thay couldn't sell us garbage.

[Mabel Adams]

I have also seen a significant uptick in false pos Fetal screens, both at my new workplace and just before I left the prior one in July. Nothing changed either place but whatever the manufacturer did.

[tar1heel]

We had this problem and after sending positive specimens to Immucor (which they got as negative), we used some PHIX to buffer our saline to a pH of 7 (we purchase blood bank saline but we had never pH'd it - when we did it was 6.0 - too acidic). The buffered saline did the trick! We retested some specimens that had been positive and they were negative. So - check the pH of your saline. If you get it between 6.9 and 7.2 you should be ok. Otherwise, buffer it!

[estiner]

Please tell us what PHIX is. We too have seen false positives and this might be helpful for us as well.

[davenoso]

Hi Kay! We feel the solution is to move FMH testing to the Flow Lab - but that process is proving to be fraught with peril -- hang in there! Diane

[babsglab]

I've had a positive fetal screen that was negative on the Kleihauer- Betke (which we have to send out to another hospital) AND I've had a kit that had such a weak positive control that I took it out of use before the outdate and switched to a more current lot that worked better. I agree the positive control "ain't what it used to be"

Babs in the lab

[AMcCord]

Phix is available from Immucor. It is a bottle of buffer to pour into a cube of non-buffered blood bank saline - one bottle per 20L cube. It is recommended by them for their automated systems. If you look for it to order on line, it is with the reagents/supplies for automation.

[babsglab]

Thank you!

Babs

[rcdjr]

I too have been having multiple false positives with the FBS kit and have been getting the same run around from the vendor. The last thing to come up was the saline also but I check the buffered saline and I'm running a pH of 7.9. We confirm all our FBS with a KB.

[dingalls2]

I haven't seen a problem-my last positive had a matching K-B stain, but I will keep pH in mind if anything develops, thanks

[rescyth]

I've never had any false positives so far for the FS but we did have some tech here that performed FS on an RH POS MOM ! and it gave a whooping 4+ reaction on tube. That's the only problem we had with the FS but it's due to technical error.

[Sue Miller]

We also have seen many false positives with negative KB stain. Immucor originally advised washing the specimen numerous times before beginning testing when this problem appeared. Sometimes that seemed to work but not always. Then they advised not washing the specimen. The current lot number seems to be doing better. We have been documenting our fetal bleed and KB results and how the specimen was treated, i.e. wash vs not washed. I sent this information to Immucor but they really did not seem very interested. They wanted to say the problem was with our saline which we have used forever. They had me do a pH on each cube we were using and all were in range.I am anxiously awaiting the to see how everyone performed on the CAP PT from November.

[huntilla]

pHiX is a phosphate buffer additive that is used on non buffered saline and is available from Immucor (six bottles to a box)

It is used for testing on the Echo and Galileo for standardizing the pH for the saline cubes(20 liter) that are used to refill the PBS supply.

[phouck]

We have not experienced any problem with our kit (pos control is just fine). What lot number are you using now? I have been here since July and have not had a problem. Take that back, did get a CAP survey negative when CAP said that it was postitive. Repeated the sample and it was positive. Very weak on the KB.

[DFields]

So if the FBS is + and the KB is NOT negative, you only give 1 dose of RhIg as long as the KB shows less than 15 ml <whole blood) of feto-maternal hemorrhage??

[Sue Miller]

The recent lot number seems to be better. Our saline always has a pH of 7.2 and we still experienced many false positives beginning about September.

[rescyth]

So if the FBS is + and the KB is NOT negative, you only give 1 dose of RhIg as long as the KB shows less than 15 ml <whole blood) of feto-maternal hemorrhage??

Yes...1 vial of RHIg(IM) can neutralize about 15ml prbc/30 WB and for the intravenous RHIg its equivalent to 17.5ml PRBC...but our institution protocol says that if the degree of FMH is >30 WB we add 1 additional vial.