The Direct Antiglobulin Test (also known as the “DAT” or “Direct Coombs” test) seems super-simple, but there’s more to it than meets the eye! Sue Johnson from BloodCenter of Wisconsin, Marquette University, and the Indian Immunohematology Initiative joins Dr. Chaffin to discuss.


Sue Johnson

Susan Johnson, MTSM, MT(ASCP)SBB

The DAT is really, in practice, a particularly basic and easy test to do. For such a simple test, however, most blood bank students struggle with the concepts, as do many clinicians! The DAT leads to discussions of autoantibodies, adsorptions, and elutions, oh my! Never fear, though, Sue Johnson is a master teacher who has taught thousands of students the essentials of the DAT! She is my guest on this episode to guide us to great clarity on this most excellent immunohematology test.

Brief Speaker Bio: Sue Johnson is the Director of Clinical Education at BloodCenter of Wisconsin, as well as the director of BCW’s Specialist in Blood Banking Program. She is also the Director of the Transfusion Medicine Program at Marquette University and Associate Director of the Indian Immunohematology Program. She has extensive experience as a teacher, author, and international lecturer; in short, she knows what she is talking about!

This is a fun episode! Whether you are a pure beginner or an experienced blood banker, you will come away with a much better understanding of why the DAT is so important!

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DISCLAIMER: The opinions expressed on this episode are those of my guest and I alone, and do not reflect those of the organizations with which either of us is affiliated. Neither Ms. Johnson nor I have any relevant financial disclosures.

The images below are generously provided by Sue Johnson. The featured image seen in the podcast episode list and on Facebook and Twitter was illustrated by Jenny O’Connor, MLS(ASCP)SBBCM.

Johnson Slide 1
Johnson Slide 2 - DAT Reagents
DAT procedure 1 - Fresh sample from patient to be tested
DAT procedure 2 - Wash thoroughly
DAT procedure 3 - Washing removes interfering free antibody (compare to slide 2)
DAT procedure 4 - Anti-human globulin agglutinates coated RBCs
Johnson Slide 7 - Complement deposition on RBCs (note C3b and C3d)
Johnson Slide 8 - Causes of positive DAT (1 of 3)
Johnson Slide 9 - Causes of positive DAT (2 of 3)
Johnson Slide 10 - Causes of positive DAT (3 of 3)
Johnson Slide 11 - Factors to consider when evaluating DAT results
Johnson Slide 12 - AMAZING flowchart for DAT evaluation!

Don’t miss these videos for a visual look at what Sue described:

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