Arno

@Bet'naSBB yep the patient was K neg.

I do not know if Malcolm's case was published (I did not find it?) but this kind of auto anti-K mimicking an allo antibody is well described in this paper issued back in 1982 Autoanti-K antibody mimicking an alloantibody, Transfusion Jul-Aug 1982;22(4):329-32, E. Viggiano et al. This anti-K was adsorbed onto and eluted from both K pos. and K neg. cells.

This phenomenon is also described with the monoclonal antibody therapy anti-CD47 (Hu5F9-G4) where red cells are so heavily loaded with IgG that it creates steric hindrance. Basically, antibodies bound to the red cells hinder the binding sites of the anti-human globulin leading from very weak to negative DAT. Anti-CD47 can be eluted off the red cells and it gives very strong reaction in IAT. Of note: it is not the same mechanism involved with the anti-CD38 (another monoclonal antibody therapy often called DARA) where here the DAT can be negative too because of down-regulation of CD38 expression onto the red cell membrane.

In this paper from 1985, "The Lui elution technique A simple and efficient method for eluting ABO antibodies c. s. FENG, K. c. KIRKLEY, c. A. EICHER, AND D. s. DE JONGH, TRANSFUSION 1985; 25:433-434.", the authors thank A. Lui. MT(ASCP)SBB, who introduced this technique to them. Therefore, I believe Lui is the name of the MT who invented this elution method.

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There are a very few cases of severe HDFN caused by anti-Kpa (see references below). I believe that in many guidelines (to be confirmed though), antibodies to Kell blood group antigen are handled, by extrapolation, the same way as anti-K due to the very few examples reported in the literature. Costamagna L, Barbarini M, Viarengo GL, Pagani A, Isernia D, Salvaneschi L. A case of hemolytic disease of the newborn due to anti-Kpa. Immunohematology. 1997;13(2):61-2. PMID: 15387785. Tuson M, Hue-Roye K, Koval K, Imlay S, Desai R, Garg G, Kazem E, Stockman D, Hamilton J, Reid ME. Possible suppression of fetal erythropoiesis by the Kell blood group antibody anti-Kp(a). Immunohematology. 2011;27(2):58-60. PMID: 22356520. Smoleniec J, Anderson N, Poole G. Hydrops fetalis caused by a blood group antibody usually undetected in routine screening. Arch Dis Child Fetal Neonatal Ed. 1994 Nov;71(3):F216-7. doi: 10.1136/fn.71.3.f216. PMID: 7820722; PMCID: PMC1061131.

When you say asymptomatic, does it mean she is not anemic? What about the reticulocyte count, bilirubin, LDH, haptoglobin? May be the mother has a compensated hemolytic anemia?

Here is an interesting paper showing that antibodies to red cell/platelet... may be transmitted via breast milk indeed, causing prolonged HDFN. Milk contains mostly IgA but IgM and IgG may be present of course and IgGs can cross the different barriers up to blood circulation (not on the same model - not actively - as the placenta though). The surprizing part here is the mother and baby are group A, A antigen is ubiquitous so the anti-A titer in breast milk should high enough to interfer with reverse group despite the adsorption of anti-A on various tissues. https://pubmed.ncbi.nlm.nih.gov/30720868/

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Here are some thoughts 1. Prophylatic anti-D given after pregnacy loss despite her D pos type and not communicated further (but sounds like the event is too old to support this option right?) 2. Can be an anti-LW instead which looks like auto anti-D (reacting stronger with D pos cells) 3. Other blood derived product given (e.g. IVIG) containing anti-D but the reaction strentgh does not support this hypothesis 4. D variants alloimmunized during first pregnancy with D pos fetus

This thread is pretty old but as it comes up again.... this "air gap" is required to avoid having the Anti-Human Globulin (AHG) present in the gel matrix getting partly "neutralized" by the excess of human immunoglobulin from the plasma. Keep in mind that plasma is full of various human Immunogloblins which will be recognized by the rabbit AHG. This "partial" neutralization may weaken the reaction indeed. Same as in tube but there is no washing step requires as the air gap is there to prevent this neutralization. Once cells are sensitized after the 37°C incubation step, the card is spun and the AHG will catch the Ig bound to the RBCs leading to positive reaction.

Is the buffer used for preparing the RBC suspension for X-Match the same as for the AC? If not, this patient may have an additional Ab to a buffer component?

Not that I am aware of. There are publications reporting an increase of DAT positive samples amongst Covid-19 patients. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7414594/ According to the authors, the eluate (IgG) reacts only with cells from Covid patients and this state is likely to be transient (related to hyperinflammation in these patients).

I don't want to advertise any specific company but in this webinar available O-D (https://info.bio-rad.com/ww-IHD-transfusion-w6-registration-lp.html), various methods are discussed (pros/cons) on how to overcome the anti-CD38 interference. I thought it could be insteresting in the context of this thread.

Sorry to hear this Malcolm. My most sincere condolences.