Due to the recurrence of requests for Direct Antiglobulin Test (DAT) and, if positive, to perform the Eluate for patients with suspected Autoimmune Hemolytic Anemia (AIHA), I come here in the hope of obtaining answers or ideas from the specialists in this group.

I understand the purpose of performing DAT (IgG/IgA/IgM and C3) to confirm cases of clinical suspicion of AIHA and/or to monitor an ongoing hemolytic process. But I wonder:

• What additional information can be obtained from the elution of red blood cells where IgG has already been detected? I understand the importance of the Eluate in the transfusion context, but knowing the methodological limitations and risks of false negatives, I cannot understand how doctors are interpreting and defining treatment based on this test.

• Is it possible to confirm a clinical suspicion of AIHA using immunohematological tests without performing the eluate? My opinion is that yes, based on some references.

My interpretation is that the eluate would be important in the laboratory diagnosis of AIHA only if DAT is negative.

I appreciate contributions.

That's an awfully big question and I am going to "try" to hit the highlights. PLEASE feel free to add or clarity anything to keep my foot out of my mouth! I will start with the standard Dat is positive. You perform an eluate and it is negative. That points to the possibility of a drug based reaction. It's the policy of some facilities to not repeat the elution if the strength of the dat has not increased in strength or a new allo antibody has been created. The elution can also help you determine if it is truly a auto or an allo antibody by seeing if the eluate reacts with DAT negative auto cells (retic harvested if needed of course). Next, what about the times when the DAT is negative? The auto could be be directed at something that is surpressed or even negative. The antibody might even be a different class of antibody such as Iga for example or perhaps a subclass of IgG that your antisera doesn't pick up. These are just a few things that I will note, quickly. Perhaps we can get Mr Needs to make a few comments. 

 

Jason Temple 

This is an interesting topic and something i worked on many years ago.  We would always do a DAT on suspected AIHA patients and would do the subclass DAT too to give us more information.  The data we obtained was combined with CR51 assay data and the Hematologic picture.  However usually and pretty quickly the DAT would max out at 4+ or 5+ depending on your facility scoring.  This made it difficult to assess the efficacy of the drug regimen i.e. is it improving red cell survival or not.  We used to quantitate IgG on the red cell using a radioligand assay to assess efficacy of drugs and guide the treatment.  is this still done now? I imagine there is another assay instead of radioligand that quantitates IgG bound to the red cell?

Many, many years ago now, when I was working at the old Westminster Hospital in London as a quite junior member of the Blood Transfusion staff, I spent quite a few hours working on a sample from a patient with a positive DAT, trying to determine the specificity, in order to see whether the antibody was an allo- or an auto-antibody.  This included the use of several very rare red cells that I had frozen down and also examining the eluate.  After many happy hours, I had got precisely nowhere, and so sent a sample to my former colleges at the International Blood Group Reference Laboratory.

I received a somewhat "spicy" report from my heroine Joyce Poole, who explained to me, in words of one syllable, that I had rather been wasting my time, rare cell collection and the laboratory's money as, in almost all cases, the specificity would be found to be an auto-anti-Rh17 or auto-anti-Rh18!!!!!

Since then, I have reverted to doing as little as possible on such samples and, when I retired 43 years later, and, as far as I know, none of the patients ever died as a result.  There was a close one once, when I was working on a sample on a Saturday on-call in the Red Cell Reference Laboratory at NHSBT-Tooting Centre.  I was working on a sample that was overtly a case of wAIHA.  After several allo-adsorptions, I was finally able to provide "suitable blood".  It was only at the last minute that the computers came back on after an unplanned downtime, and it appeared that the patient was known, from many years previously as having an allo-anti-Vel!!!!!!!  As you can imagine, I did several more tests before I released the blood (on Pathologist's orders), as there was absolutely no evidence of an anti-Vel (auto- or allo-) in the present sample - but it did give me a bit of a turn!!!!!!!!!!!!

I would recommend a thorough reading of Petz LD, Garratty G.  Immune Hemolytic Anemias.  2nd edition, 2004, Churchill-Livingstone. ISBN  978-0-443-08559-8.

Other than that and, possibly, looking at the patient's sample at a more molecular level (as noelrbrown suggests above), I really wouldn't do much else, except that I would put a little note with the blood to be transfused to remind the doctors and nurses on the ward to be vigilant with their patient observations.

ALL OF THE ABOVE HAVING BEEN SAID, I AM NOT, AND NEVER HAVE BEEN, MEDICALLY QUALIFIED!!!!!!

Edited January 21Jan 21 by Malcolm Needs
Spelling (as ever!).

Agree that in “not recently transfused”patients, eluates are of no clinical use unless you like seeing panagglutinins.😜 Negative eluates occur in some drug dependent examples but the clinical information is paramount in such situations in any case.

Agree with Dr Blumberg. In an abstract from way back, 1996, Ann Church studied the value of an eluate, reference and abstract below (apologies for quality of print). 

A Church, S Nance, D Kavitsky.  Assessment of Elution Studies in Cases with 37^OC Reactive Serum Autoantibodies (SA).  Transfusion 1996; 36:161S (Suppl)