40 Antibody Screening (ABS) by Gel Method (G-IAT)

Principle

The antibody screen test is used for the detection of unexpected blood group antibodies. In this test, 0.8% Screening Cells ( reagent red cells) are combined with patient serum/plasma. The Gel-card includes anti-IgG and  a potentiating medium (low ionic strength saline/solution or LISS) which promotes antibody/antigen reactions to occur quickly. Positive reactions at any phase of testing indicates the presence of an  allo- or auto-antibody.

An autologous control, is included in antibody investigations of positive antibody screen tests. Antibody investigations should be performed using the same method in which the ABS was performed, to test patient plasma and red cells under the same conditions as the antibody screen test. Incubation and the presence of enhancement/potentiating media may cause reactivity in the autologous control that is only an “in-vitro” phenomenon; an auto-control is expected to be negative.

Related Policies

This procedure applies to all testing that requires antibody screening.

Specimen

Serum or plasma may be used. Specimen age must comply with policies and procedures of the institution. CAN/CSA Z902 Blood and Blood Components standards indicate “the sample shall be collected within 96 hr prior to the scheduled transfusion if:

• The recipient has been transfused with a blood component containing red cells within the previous 3 months
• The recipient has been pregnant within the previous 3 months; or
• The recipient’s history is questionable or unavailable

For repeat recipients, the original sample may be used to crossmatch additional units within the 96 hr period following transfusion of the first unit of blood.”

Reagents

1. Gel Cards (Anti-IgG)
2. Screening Cells(SC) – 0.8%.(commercially available un-pooled group O cells)
3. MTS-Diluent (for auto control as required)

Procedure

1. Visually inspect the gel card(s) for dryness, bubbles.
2. Label gel card with I,II,III in the small block under each  gel card well. Gel cards have 6 wells, so can be shared or used for two patients.
   1. Next to well III put a small line to divide card in half and record patient identification and your initials on the white area of the gel card under I,II,III, this a ssigns the microtube well results to the patient.
3. Remove the foil from the wells that are to be used; if only 3 wells lift the foil to expose the appropriate wells and cut it once wells are open. Leave remaining wells covered with foil.
4. Using an approved pipette Add 50 ul of SUSPENDED 0.8% SC I to the well labelled I; be careful not to touch the gel card with the pipette tip, hold straight and steady above the well then dispense into the well without touching the gel card with the pipette tip. With fresh tips, repeat for SCII and SCIII until all 3 wells contain appropriate SC.
5. Add 25ul of plasma/serum to the wells, I, II, and III.
6. Incubate the gel cards according to manufactures directions, at 37 +/- 2 ℃ for 15 minutes.
7. After incubation, centrifuge gel card for 10 minutes.
8. Grade and record results.

 Interpretation

1. The presence of agglutination/hemolysis may indicate the presence of an unexpected antibody.
2. The absence of agglutination/hemolysis is a negative result.

Notes

1. The Antiglobulin test must be completed without delays. Interruptions or extended delays may result in false negative and /or positive results depending on which phase of testing is impacted.
2. If tests with all reagent red cells are reactive, the possibility of spontaneous agglutination should be considered- an auto control test should be nonreactive.
3. Gel testing is more sensitive than other methods and may result in the detection of nonspecific reactivity.