Titrate anti-Lu b?

[Mabel Adams]

We have a pregnant patient with anti-Lu b.  Because of the variability of the antigen strength and the likely mild impact on the baby, is it recommended that we try to provide titers of this antibody?

[Malcolm Needs ☆]

I wouldn't bother, to be honest.

Apart from the fact that the Lutheran antigens vary in strength of expression, making it difficult to ensure that the recorded titres would "match up" one to another, but the expression of the Lutheran antigens on foetal and cord erythrocytes is known to be weak.  On top of that, of course, there is the problem of finding a regular source of adult erythrocytes with heterozygous expression.

In addition, anti-Lu^a and anti-Lu^b can be either IgG or IgM but are more commonly IgM.  It might be worth your while treating the maternal plasma/serum with a reducing agent such as 0.01M dithiothreitol, 2-mercaptoethanol or ZZAP to see how much, if any, IgG is present.

Even if the antibodies are IgG, they are thought to be adsorbed on to foetal Lutheran glycoprotein on the placental tissue.

Lastly, as you so rightly say, clinically significant HDFN caused by anti-Lu^b is incredibly rare, and so, all in all, you could be giving yourself an awful lot of work for very little return.  If you do decide to test the maternal plasma/serum with reducing agent, and you find that there is an element of IgG present, it might be worthwhile just performing a titre once, in order to see that you have not got one of these incredibly rare examples that might cause clinically significant HDFN, and, as lone as the titre isn't massive. I would rest easy.

If you want, I can cite references to back up what I have written above, but I haven't done so straightaway, as actually finding some of these papers to read is equally hard work!!!!!!!!!!

I hope that helps.

[Mabel Adams]

Thanks for your input.  I was hoping you might respond.

The Daniels book says that "No case of HDFN caused by anti-Lua or -Lub and requiring any treatment other than phototherapy is reported, although raised bilirubin or a positive DAT may be detected."  Does this description equal "clinical significant HDFN" by your definition or is there newer information on more severe HDFN from these since Daniels published the 3rd edition?  My thought is that, if there is no evidence of any case needing any early intervention, then there is no point in running titers to determine when to begin early intervention.

 

[Malcolm Needs ☆]

No Mabel.  As always, Geoff is ABSOLUTELY right (and I would NEVER, in any case, go against one of the world's GREATEST in terms of Blood Group Serology).  Thank you also for your kind words, and I totally agree with your conclusion.

[Mabel Adams]

Consensus I am getting from other sources is that we should either defer to our medical director (who doesn't feel comfortable making the call not to titrate on her own) or we confer with the obstetric providers and decide as a team what makes the most sense for this patient.  As long as the titer remains quite low, we could probably trust it.  If it approaches 16 (not a cut off determined with Lutheran antibodies in mind) then we couldn't be sure of its precision (to the extent any titer series is precise) but it would not be harmful to move to monitoring with Doppler US--just more expensive.

[Malcolm Needs ☆]

26 minutes ago, Mabel Adams said:

Consensus I am getting from other sources is that we should either defer to our medical director (who doesn't feel comfortable making the call not to titrate on her own) or we confer with the obstetric providers and decide as a team what makes the most sense for this patient.  As long as the titer remains quite low, we could probably trust it.  If it approaches 16 (not a cut off determined with Lutheran antibodies in mind) then we couldn't be sure of its precision (to the extent any titer series is precise) but it would not be harmful to move to monitoring with Doppler US--just more expensive.

To a VERY large extent I agree with you, if for no other reason than, it is NOT for laboratory workers to decide on the way a patient is treated (including monitoring during pregnancy).  That having been said, no medical director can be expected to be an expert in ALL aspects of medicine, including pregnancy and foetal medicine, and so a good medical director should be prepared to take advice from world famous scientists, such as the late Prof Dave Anstee, and the very much alive Dr Geoff Daniels.