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Answering your questions: EDTA "pink top" tube for blood bank.

Q I recently read in my immunohematology textbook, Immunohematology principles and practice, 2nd ed., by Eva D. Quinley, and have heard in a recent lecture that the preferred specimen for ABO and Rh typing is non-anticoagulated specimen, or one anticoagulated with heparin in order to preserve complement. My question is how did the standard blood-collection tube for blood bank become the EDTA "pink top" tube? EDTA binds calcium and thereby inhibits complement activation.

[ILLUSTRATION OMITTED]

A According to American Association of Blood Banking standards (22nd ed.), either plasma or serum can be used for pretransfusion testing. (1) While transfusion-service use of EDTA samples is not yet "the standard," it is becoming more popular for a number of reasons. Serum that is incompletely clotted can yield spurious results, and serum-separator tubes that accelerate clotting cannot be used for transfusion testing. Given the need for rapid turnaround, waiting for specimens to clot is a delay that many trauma patients cannot afford. Patients on anticoagulants can also experience significant delays in getting blood ready because of prolonged clotting times. A major advantage with using EDTA is that testing can begin as soon as the specimen arrives in the lab, with no waiting for clotting. As the questioner implies, the concern with using EDTA-stabilized specimens is that there are clinically significant antibodies that can be detected only when activated complement is present (especially J[k.sup.a] and J[k.sup.b]). By blocking complement activation, EDTA impairs our ability to detect these antibodies. While this is a well-recognized limitation of EDTA, most clinically significant non-A, -B, -O antibodies are IGG molecules; and we are not reliant solely on complement for their detection. The increased use of gel-/solid-phase methods for antibody testing has increased interest in use of EDTA because these methods seem to perform more reliably when plasma is used. (2) Validation studies and clinical trials done over the last decade have shown that the combination of EDTA-stabilized specimens, monospecific IGG reagents, and gel-/solid-phase testing is fast, safe, and reliable. (3)

While no perfect method for antibody screening has yet been found, many blood bankers have concluded that EDTA is a practical compromise

that meets the needs of most patients.

"Our labs are much more than technology. They are the dedicated people who go the extra mile to provide service to our patients. Keep up the good work."--Daniel M. Baer, MD, MLO editorial advisory board

References

(1.) Menitove JE, ed. Standards for Blood Banks and Transfusion Services. 22nd ed. Bethesda, MD: American Association of Blood Banks; 2003.

(2.) Scott Y. Comparison of plasma and serum for antibody detection using DiaMed microtubes. Transfus Med. 1996;6(1)65.

(3.) Titlestad K. Detection of irregular red cell antibodies: more than 3 years of experience with a gel technique and pooled screening cells. Vox Sang. 1997;73(4):246-251.

Edited by Daniel M. Baer, MD

--Richard M. Scanlan, MD

Director, Transfusion Medicine

Oregon Health and Science University

Portland, OR

MLO's "Tips from the Clinical Experts" provides practical, up-to-date solutions to readers' technical and clinical issues from a panel of experts in various fields. Readers may send questions to Dan Baer by e-mail at tips@mlo-online.com.

Daniel M. Baer, MD, is professor emeritus of laboratory medicine at Oregon Health and Science University in Portland, OR, and a member of MLO's editorial advisory board.
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Title Annotation:Tips from the clinical experts
Author:Scanlan, Richard M.
Publication:Medical Laboratory Observer
Article Type:Column
Date:Apr 1, 2006
Words:560
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