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hollowayl

HbS neg requirement

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No guidelines, just clinical common sense.  There are absolutely no data to support the need for excluding heterozygous donors, nor the need for heterozygous recipients to receive only AA blood.  Heterozygous patients are physiologically normal except for some data to suggest that under extreme conditions of dehydration, altitude they are slightly more susceptible to complications that occur even among hemoglobin AA patients.

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We have a pretty big (and growing) Adult Sickle Cell Clinic with a majority of the patients getting Erythrocytapheresis for their disease.  We give all our patients sickle negative RBC’s.  The reason I was given was that when tracking the Hgb concentration (A, A2, S, C, etc.) by hemoglobin electrophoresis, we want the results for the patient, not the Hgb S positive unit that we are transfusing them.  We are told the doctors adjust treatment based on the hemoglobin electrophoresis levels.

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Posted (edited)

One unit of hemoglobin AS blood will contribute perhaps 5% to the S level in a patient with hemoglobin SS whose overall post-apheresis hemoglobin level is 10 g/dl.  Not enough to make a real difference.  A lot of work for pretty much nothing in my view.  But we do it anyway.  Probably would be less work to test donor units if the %S doesn't drop quite as far as expected.  Hemoglobin S in AS red cells does not behave the way it does in SS red cells, so this has absolutely no clinical implications.  The hemoglobin S goal for most treatment is 30% or less.  5% is not going to make any difference in treatment plans.  Just an alternative view from the usual :).

Edited by Neil Blumberg

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I’m certainly not a doctor, but from a technologist perspective, when we give the clinician a Hgb S level of 35% and their goal was 30% or less for their patient suffering from Acute Chest Syndrome, I know we will be getting another order for an Erythrocytapheresis meaning we have to find 6-8 more units that are negative for C, E, and K antigens and all the other antibodies they may have developed to get their Hgb S level below 30%. 

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" I know we will be getting another order for an Erythrocytapheresis"

That's not to say that is good clinical judgment.  There is not a shred of evidence that 30% is better than 35%, and to expose the patient to the risk of another 6-8 units of red cells and an invasive procedure is, in my opinion a serious misreading of the benefits and risks of transfusion in this setting.  Not to mention that the same goal (30%) could be achieved by simple  transfusion of AA red cells.  But neither apheresis exchange nor transfusion is indicated for clinical benefit.

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One might add that use of transfusion in acute chest syndrome has almost no evidence base and may indeed do more harm than good.  In transfusion, less is usually better than more.  

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