Fetal Screen

[paddleking]

Getting lots of positive controls from our Immucor sets.  Currently, we had 3 in a row so now have to do a KB instead until it is resolved.

Is anyone else having this problem?  How did you resolve it?

[AMcCord]

We haven't been having problems with our kits, but investigations for two survey failures for false positive results a few years ago pointed to the wash step as critical. Maybe start there. What works for us is a 12 x 75 tube filled to near the top, decant well after each of the 4 washes, make sure to break up the cell button prior to adding saline, and make sure that the saline addition is well mixed (uniform color throughout the tube). We had problems when we were using NERL saline. We now use unbuffered saline with pHix added (same that runs on the Echo). I had techs that tended to fill the tube only 2/3 full with saline for the washes and who weren't making sure the saline/cells were well mixed. Changing that habit seems to have helped. 

[SbbPerson ☆]

Strange , we have never had that problem. We use immucor too.  I agree with AMcCord, washing is critical for this test.  Also, how are you counting the agglutinates?  By tube or slide? If you see agglutinates by tube, you should do it also on slide so you can count the number of agglutinates per LPF.   If you get less than 5 agglutinates in 5 fields, it is negative. 

Edited December 24, 2022 by SbbPerson
spellin

[paddleking]

We count under slide.  We wash with buffered saline, but not with PhiX added to unbuffered.  We purchase isotonic phosphate buffered saline from thermo scientific.  We have a sister hospital that follows the same procedure and reagents and they have not had issues.  Talking to Immucor we are the only customer that has reported issues with this.  We have gone through 3 lots.  I have checked the pH of the saline and it is 7.02, which is perfect.  We have washed both manually and with automated cell washers.  

Anyone have any additional thoughts or directions I should go?

[SbbPerson ☆]

On 12/28/2022 at 8:33 AM, paddleking said:

We count under slide.  We wash with buffered saline, but not with PhiX added to unbuffered.  We purchase isotonic phosphate buffered saline from thermo scientific.  We have a sister hospital that follows the same procedure and reagents and they have not had issues.  Talking to Immucor we are the only customer that has reported issues with this.  We have gone through 3 lots.  I have checked the pH of the saline and it is 7.02, which is perfect.  We have washed both manually and with automated cell washers.  

Anyone have any additional thoughts or directions I should go?

Does your sister hospital uses the same Lot numbers of Immucor FBS kit? If yes, then you guys must be doing something wrong.  When was the last time your cell washer/centrifuge was calibrated? RPMs? Amount of saline dispensed? 

If they are not using the same Lot #'s, perhaps give them one of your kits and see if they get the same result. If the kit's QC passes for them, then there is something wrong with either your procedure or maybe equipment.  This is really strange. Good luck. 

 

 

[SbbPerson ☆]

Also this test should only be performed on Rh negative moms. And do not use any other Anti-D reagent, use only the one included in the kit.  

 

Anyways, I attached the AABB procedure to this test. I hope this helps a little. Good luck. 

AABB_FBS.docx