DAT Testing Post-Transfusion

[jhaig]

According to AABB, you should perform a DAT on patients that have been transfused within the previous 3 months. Our reference lab will only do one if the transfusion had occured within the previous 30 days. I'm not 100% sure where they got the info to adopt this protocol, but is there any documentation out there that will let me change my protocol to 30 days rather than 3 months? Last time I checked 3 months was the accepted standard.

[SMW]

Could you please provide the specific AABB Standard you're referencing? I am unaware of an AABB Standard (or any other US standard or regulation for that matter), that specifies a required frequency for routinely performing a DAT (with the exception of a transfusion reaction investigation).

[jhaig]

Could you please provide the specific AABB Standard you're referencing? I am unaware of an AABB Standard (or any other US standard or regulation for that matter), that specifies a required frequency for routinely performing a DAT (with the exception of a transfusion reaction investigation).

I agree that there's no specific standard, but I'm referring to the AABB technical manual 15th ed, pg 455 "Many workers routinely attempt to determine the cause of a positive DAT when the patient has recevied transfusions within the previous 3 months". I just don't know how to adjust my protocol because I can't find any documentation to back me up. Is this something I can change based on my patient population or are there any specific guidelines to follow?

The AABB manual also goes on to say that "antibody may appear as early as 7 to 10 days (but typically 2 weeks to several months)". That, to me, leaves a lot open to interpretation.

[ckcheng]

Perform DAT on pre-transfusion sample is not necessary. Do when you perform antibody workup or transfusion reaction investigation. Also, DAT can be use to exclude or include a hemolysis is due to immune complex (antigen-antibody reaction).

CK Cheng, MSc, SBB(ASCP), CQA(ASQ)

Hong Kong

July 8, 2009

[SMW]

The section you refer to in the Technical Manual is for the evaluation of a positive DAT, not necessarily what tests should be performed as part of pre-transfusion testing. And as a reminder, although published by the AABB, the Technical Manul is a textbook and not regulations or standards of the association.

It has been known for some time now that there is little predictive value of a DAT for detecting an early response to clinically significant antibodies in recently transfused patients. [see Judd WJ, Barnes BA, Steiner EA, et al. The evaluation of a positive direct antiglobulin test (autocontrol) in pretransfusion testing revisited. Transfusion 1986;26:220-4.] Many US facilities currently do not routinely perform a DAT (or autocontrol) as part of the routine pre-transfusion testing regardless of transfusion history unless the antibody screen results are positive. On the other hand, the recent transfusion history would be important to be considered in the evaluation of a DAT that has been requested and performed for the typical diagnostic evaluations of a suspected transfusion reaction or evaluation of a hemolytic process and would determine what additional tests (if any) might be considered.

For re-considering your protocol for the evaluation of a positive DAT in a recently transfused patient, in addition to above article you may want to also review Judd et al. [The evaluation of a positive direct antiglobulin test in pretransfusion testing. Transfusion 1980;20:17-23]. After testing and evaluating a number of samples, that group restricted serologic evaluation of a positive DAT to only those samples from patients transfused within the previous 14 days. They further note “…because the predictive value of a positive antiglobulin crossmatch is higher than that of a positive DAT when screening tests for unexpected serum antibodies are negative, it seems inappropriate to eliminate the antiglobulin crossmatch yet continue to perform a DAT or autocontrol.†The reference lab protocol of 30 days (and I’m assuming this is a sample that demonstrated a positive antibody screen) seems well within the accepted parameters of only performing tests that are likely to reveal clinically useful information.

[tbostock]

This is correct, the DAT is not required as part of pretransfusion testing.