RhIg

[Lindz82]

In maternal specimens...Out of curiosity... How strong can RhIg be (in gel column)? How long after dose is given will it still show up?

Is there any way to ensure that it is actually RhIg and not Anti-D?

Thanks for the Info!

Lindsay

[Malcolm Needs ☆]

In maternal specimens...Out of curiosity... How strong can RhIg be (in gel column)? How long after dose is given will it still show up?

Is there any way to ensure that it is actually RhIg and not Anti-D?

Thanks for the Info!

Lindsay

This is an almost impossible question to answer.

I've seen reactions as strong as 3+ as a result of anti-D immunoglobulin, but I have also seen 3+ reactions given by an alloanti-D with a strength of 932IU/mL, presumably because of antigen swamping (for those of you unfamiliar with the UK way of measuring anti-D levels, we get worried when the level reaches anything above 4IU/mL, and there is usually hydrops with a level of 20IU/mL, without intervention).

It also depends upon the dose given, and when. In the UK, we use many different doses (the most common being 250IU, 500IU, 1250IU and 1500IU). The foremer 2 doses can usually be detected for 8 weeks by IAT post administration, but the latter can often be detected for at least 12 weeks.

One can usually detect the anti-D within about 48 hours of the dose given, but all women are different of course. Some absorb it into their circulation quicker, whilst others much slower (and some never absorbit at all, and the prophylaxis fails).

At present, I don't know of a way of absolutely showing the difference between immune anti-D and prophylactic anti-D. I suppose one way of doing it would be to test the Gm and Km antigens on the anti-D. If it is imune, then the Gm and Km types will all be the same, but if it is immune, the will be a mixture (as the prophylactic anti-D will come from a blend of plasmas), but I would not recommend this method, as it takes ages, decent anti-Gm and anti-Km antisera are difficult to come by, and the method has never been validated. It will be evn more difficult when the prophylactic anti-D becomes monoclonal as, of course, this will also be from a single source.

Sorry, I know that this is not a very hopeful (or helpful) answer.

:(:(

[Malcolm Needs ☆]

I should also add, of course, that the size of the lady involved is also a factor.

[Malcolm Needs ☆]

And I should also have added that it depends upon the way the individual catabolises (if that is the right word) the IgG.

[Lindz82]

Thanks for the input Malcolm. I just have a hard time telling a client hospital it is probably RhIg when it is reacting 3+... I worry it is allo-anti-D and I may lead tham astray...

[tbostock]

We've seen anti-D from RhIg administration go as high as 3+ in gel, so there is really no way to distinguish "real" anti-D from anti-D from RhIg in the transfusion service setting. We've also had it show up very quickly, the next day after administration; so our only recourse is a good patient history. Usually the OB's office can give us a date of RhIg administration that correlates with what we are seeing in the gel.

[AMcCord]

We've seen patients who were given RhoGAM in the office and sent immediately to us to have an antibody screen drawn (cart before the horse). Our specimens were drawn less than 1 hour post administration and our gel reactions were 3 and 4+. We begged that office to please not do that anymore...

[L106]

I think most of us see passive Anti-D due to RhoGam as 3+ reactions in gel or with automation that we used to see as only micro or 1+ with tube technique.

[Mabel Adams]

You are safest to assume it is passive anti-D and still give RhIG. If necessary, the case can be followed by titrations every few weeks--passive anti-D should decrease (until they give another dose anyway). If active, you will be monitoring the titers so will avoid any disasters to baby, but this is seldom necessary in a case with a clear history.

[Malcolm Needs ☆]

You are safest to assume it is passive anti-D and still give RhIG. If necessary, the case can be followed by titrations every few weeks--passive anti-D should decrease (until they give another dose anyway). If active, you will be monitoring the titers so will avoid any disasters to baby, but this is seldom necessary in a case with a clear history.

I agree entirely with this Mabel.

The danger from giving unnecessary anti-D immunoglobulin (even though it is a human blood derivative, and may contain a blood-borne transmissible virus) is minimal, compared with the known (and much more common) danger of haemolytic disease of the foetus/newborn.