To perform the serologic crossmatch, two samples must be collected, as follows:
An immediate spin phase is performed with donor RBCs prepared as a 2%-5% suspension in normal saline or ethylenediaminetetraacetic acid (EDTA) saline and the patient's serum. Both samples are mixed together and centrifuged at room temperature to visualize hemolysis or agglutination, which would signify a positive test result and the presence of an additional antibody. Crossmatch-incompatible blood is rarely encountered, because donor blood units are selected after an effective antibody screen. When only the type and screen are combined with the immediate spin phase, this is known as an abbreviated crossmatch [4] and it is 99.9% effective in preventing an incompatible transfusion. [5] The benefits of the abbreviated crossmatch include decreased cost and quicker blood availability. Further testing is unnecessary if no antibodies are identified with the immediate spin phase. However, if agglutination occurs during the immediate spin phase, one of the following situations may have occurred:
When the immediate spin phase is positive for agglutination or hemolysis, further testing is required. The donor unit is deemed incompatible for transfusion, and the antibody responsible for the reaction should be identified. The next phase of testing consists of the antiglobulin crossmatch, which may be performed via column agglutination, solid-phase systems, or tube. The antiglobulin crossmatch is the major component of a full serologic crossmatch. 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. In an antiglobulin crossmatch performed using the column agglutination system, the donor RBCs, suspended in a hypotonic buffered saline solution, are mixed with the recipient’s serum or plasma to allow antigen-antibody interaction in the upper chamber of the microtube. The antibody in the recipient’s serum or plasma is detected when the sensitized donor RBCs react with the anti–immunoglobulin G (IgG) in the microtube during centrifugation. Agglutination or hemolysis constitutes incompatibility between the donor RBC unit and the recipient’s serum. As shown in the image above (gel testing), the migration of donor RBCs through the tube is graded between 0 (representing no agglutination) to 4+ (the maximum amount of agglutination). Before performing tube testing, it is advantageous to wash and resuspend donor RBCs in 2%-5% saline to remove small fibrin clots and some cold agglutinins. The ratio of patient plasma or serum to donor RBCs is also important, as too many donor RBCs could result in a false-negative result if there are not enough antibodies binding to the RBCs to cause a reaction. The crossmatch incompatibility detected in antiglobulin crossmatch can be associated with the following conditions:
In the computer crossmatch, there is no mixing of the donor RBCs and patient serum. Instead, a computer verifies the ABO/Rh compatibility. [4, 6] This procedure may be used in lieu of an immediate-spin phase and antiglobulin crossmatch if certain criteria are met, as follows:
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401. Basic Science and Clinical Practice in Blood Transfusion| November 15, 2013
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