What would cause the ID to be negative

[bbnewbie]

I work in a reference lab and had a patient that had a positive antibody screen (1+) so it was sent for an antibody ID. This came back as anti-D too weak to titer. The doctor waited 4 weeks and did another antibody Id but this time it was negative. We dont have any patient info except age and sex. What would cause the ID to be negative???

Thanks

[RR1]

Possibly due to anti-D prophylaxis (Rhogam) given up to 8-12 weeks prior to the positive screen. After this time the antibody may have cleared.

However you would need to have evidence that she was given this dose and also if this was the case, that her antibody screen prior to administration was negative.

[ckcheng]

Antibody workup needs patient medical and transfusion history. I suggest you request them from the patient's transfusion center or physician. Otherwise report the result negative directly, or add comment depends on the practice of your institute.

4 weeks ago weak pos, now becomes neg most likely due to titer dropped. Others like cells selection, method use, and most important is sample properly stored , not deteriate, during transportation.

CK Cheng, MSc, SBB(ASCP), CQA(ASQ)

Hong Kong

Apr 30, 2009

[Hi-Freq]

I work in a reference lab and had a patient that had a positive antibody screen (1+) so it was sent for an antibody ID. This came back as anti-D too weak to titer. The doctor waited 4 weeks and did another antibody Id but this time it was negative. We dont have any patient info except age and sex. What would cause the ID to be negative???

Thanks

RhoGam is your most logical answer, but you would need verification from her physician's office. I work in a very large reference lab and we see this a few times a week. We always call the physician's office to confirm the date of RhoGam injection, and attempt to explain that when ordering the prenatal work-up, they can save a lot of unnecessary time (and money) by directing the patient to have her blood drawn for the antibody screen first, then giving her the RHIG injection afterwards. Often they do not do that because they want to give the patient the RhoGam before they get out of the office (for fear they will not come back) - but it's worth a try.

[John C. Staley]

Keep in mind that any antibody can and will "drop below detectable levels". While some are more likely(anit-Jka comes to mind) than others. I've seen anti-D do it as well as anti-S and others. It just happens, generally in older patients, they even have their anti-A or anti-B disappear sometimes.

Having said all that I agree that the most likely cause for your scenerio would be RhIG but without a little history it's only speculation.

[ckcheng]

Yes, I agree with John Staley, go and get patient medical history cuz they are very helpful in antibody workup and transfusion reaction workup. You may consider to add a column of [Patient History], and require all refer-in cases to fill so you do not have to ask every time.

CK Cheng, MSc, SBB(ASCP), CQA(ASQ)

Hong Kong

May 1, 2009

[Malcolm Needs ☆]

I work in a reference lab and had a patient that had a positive antibody screen (1+) so it was sent for an antibody ID. This came back as anti-D too weak to titer. The doctor waited 4 weeks and did another antibody Id but this time it was negative. We dont have any patient info except age and sex. What would cause the ID to be negative???

Thanks

This is a bit "left field", but the other thing it could be is a transient auto-anti-LW. If the patient has had an infection, he or she could transiently loose their own LW antigens and produce what appears to be an allo-anti-LW. As the patient gets better, so the antibody disappears and the antigens reappear.

Anti-LW does, of course, often mimic anti-D, but cord RhD- red cells are strongly LW+, and this is one way of telling the difference.

I do, however, think that anti-D immunoglobulin prophyaxis is much more likely.