How are antibody screening test results interpreted?

Updated: Jun 24, 2019
  • Author: Ashok Tholpady, MD, MSc; Chief Editor: Jun Teruya, MD, DSc, FCAP  more...
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If the screening result is positive in any of the 3 phases with any of the screening cells, additional tests must be performed to identify the specificity of the antibody. As a result, antigen-negative blood is given to the patient for safe transfusion.

In a negative reaction, the pellet passes easily to the bottom, as no agglutination occurs. This is scored as a "0." In a positive reaction, antibodies in the patient's plasma bind to RBCs and obstruct passage to the end of tube. The strongest reaction occurs when the RBCs remain at the top of the tube, scored as a "4+." See the following image.

Gel testing. Agglutination is graded on a scale fr Gel testing. Agglutination is graded on a scale from 0 to 4+. A: 4+ reaction = red blood cell agglutinates (RBCAs) remain at the top of the gel; B: 3+ reaction = RBCAs remain in the top half of the column; C: 2+ reaction = RBCAs are scattered throughout the column; D: 1+ reaction = RBCAs are primarily in the lower half of column; E: 0 = no agglutination and red blood cells pass all the way to the bottom.

With SPRCA, a positive reaction is noted by indicator RBCs becoming dispersed throughout the well, because their surface anti-IgG antibodies bind to any antibody attached to the fixed RBCs. In contrast, a negative reaction forms a tight button in the center of the well.

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