Subject: Antibody Detection Test; Gel Method
ANTIBODY DETECTION TEST; GEL METHOD
PURPOSE
To detect unexpected blood group antibodies in blood donors or recipients.
PRINCIPLE
The antibody detection test (“antibody screen”) tests the plasma or serum of a patient or donor for the presence of unexpected RBC antibodies. In the gel test system for antibody detection, reagent RBCs in a hypotonic buffered saline solution are combined with plasma/serum in the upper chamber of a microtube where antigen-antibody interaction can occur. The RBCs are then forced by centrifugation through a gel suspended in a solution containing anti-human globulin. If RBC antibody is present, RBC agglutinates form which cannot migrate easily through the gel and are retained. If no agglutinates form, single RBCs pellet at the very bottom of the microtube. The difference between agglutinates "hung up" in the gel and RBCs pelleted at the bottom of the tube is readily visualized.
The sensitivity of the antibody screen is limited by the presence or absence of antigens present on the screening cells. These cells are selected to detect most clinically significant antibodies. Since screening cells are group O they will not detect anti-A1 or other ABO antibodies.
MATERIALS AND SPECIMENS
See General Guidelines for serologic testing, procedure # 201
Patient Blood Bank Record, appendix 210.1 or other patient worksheet.
POLICIES
1.An antibody detection test(“antibody screen”) must be performed on all candidates for transfusion. In an emergency, blood can be issued prior to completion of the antibody screen with the approval of the patient’s physician.
2.Antibody screening for pretransfusion testing must be performed within 3 days of specimen collection.
3.For patients/donors with antibody(ies) demonstrated in a previous workup, the antibody screen test is performed with a cell panel comprised of RBCs selected to rule out clinically significant antibodies other than those the patient has already formed, along with one RBC which is antigen positive for each antibody the patient has already formed (refer to procedure #221 for selection of these cells). If the antibody(ies) become undetectable, the following study may again start with an antibody screen.
4.An antibody screen must be performed on all whole blood and platelet donors.
PROCEDURE
- Allow reagents and specimens to come to room temperature before testing (see procedure #201, General Guidelines for Serologic Testing" for reagents and specimen requirements).
2.Label the gel card with the patient's identification, the cells to be added, and the date and time of the test (see procedure #201 for labeling requirements).
3.Remove the foil seal from the card for the number of microtubes that will be used.
NOTE: Do not remove the foil until you are ready to perform the test.
4.Add 50 µl of each 0.8% antibody screen cell suspension to the correct microtube(s) using an appropriatemechanical pipette.
5.Add 25 µl of plasma or serum to the correct microtubes using the pipette.
6.Incubate at 37C for 15 minutes. Incubation may be extended to 40 minutes (see manufacturer’s instructions).
7.Centrifuge the gel card for 10 minutes.
8.Read the front and back of each microtube macroscopically, and record the results as negative or positive.
Procedure Notes
1.Red cells must be added to the gel card within 1 hour of removing the foil. If more than 1 hour has elapsed since removing the foil, the gel card is unsuitable and must be discarded.
2.Plasma or serum must be added, and the card placed in the incubator, within 10 to 15 minutes of adding the red cells to the reaction wells.
3.Reactions must be read within 1 hour of centrifugation.
4.If centrifugation has been interrupted, the test must be repeated; do not re-centrifuge the gel card(s).
5.Clots, fibrin or particulate matter in plasma or serum may cause anomalous results. For this reason if a clotted sample (red top tube) is used, adequate time must be allowed for complete clotting.
INTERPRETATION OF RESULTS
No agglutination or hemolysis of the screening cells in the gel card is a negative test result and indicates the absence of a blood group antibody in the plasma specimen.
Hemolysis or agglutination of any of the screening cells in the gel card indicates the presence of an antibody directed against an antigen which is present on the screening cells. A positive antibody screen must be investigated as outlined below.
Resolution of a Positive Antibody Screen
Initiate antibody identification as outlined in procedure #221, Investigation of a Positive Antibody Detection Test. For patients urgently needing transfusion, consult the blood bank physician immediately. Prior to the serologic resolution, the technologist must:
1.Initiate an Immunohematologic Problem Worksheet with patient identifiers, location, physician, etc.
2.Call the clinical care unit/hospital of the patient to notify them of the positive result and to request:
a.Additional samples if needed.
b.Patient diagnosis, transfusion history, and medications and enter on the worksheet.
c.Information on the urgency of the blood request.
REFERENCE:Manufacturer’s package inserts
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