50 Crossmatch GEL-MTS Method

Principle

The serologic Gel-IAT crossmatch is used to detect blood group antibodies in the serum/plasma of a recipient to antigens on donor RCs. The RCs are combined with patient serum/plasma to allow antigen-antibody interaction.  The immediate-spin (IS) crossmatch provides serologic testing to detect ABO incompatibility only. The completion of the crossmatch by Gel-IAT testing permits detection of incompatibility caused by antibodies (IgG)that react with cells at 37°C. This crossmatch is required when a patient has an identified or previously identified clinically significant red cell allo-antibody.

Related Policies

This procedure applies to compatibility testing of all transfusion recipients with clinically significant antibodies.

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 h 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 h period following transfusion of the first unit of blood.”

Reagents

1. Gel Cards(Anti-IgG).
2. Donor RCs; from segments attached to the units to be transfused.
3. Isotonic Saline
4. MTS Diluent 

Procedure

1. Label 2 sets of tubes with patient name, donor unit number and test identification (XM).
2. If RC segments are available, remove a segment from the unit and place it in the appropriate labelled tube; this becomes a neat donor red cell tube and is used to Prepare a 0.8% red cell suspension. As follows:
   1. Add 1 ml of MTS diluent to the second (empty)labelled tube
   2. Add 10 ul of donor red cells to the above diluent, this is your donor 0.8% working cell suspension.
3. Visually inspect Anti-IgG gel card for dryness and air bubbles.
4. Label Gel card well as XM1, XM2 ….as needed, in small squares below wells, include patient information in white area under wells assigned to patient and your initials. Only remove the foil from the wells required for testing.
5. Add 50 ul of 0.8% donor cells (XM1,XM2 …) to the appropriate well, pipette all cells to each well before adding plasma/serum.
6. Add 25ul of plasma/serum to XM1, XM2 …. wells in gel card, can use multipipettor
7. Visually inspect volume in each card gently tap to assure all liquids are together..
8. Place gel card in MTS Gel card incubator for 15 minutes at 37 +/- 2℃ ; document time of incubation on the worksheet.
   1. During incubation perform an ABO -I.S. XM between patient plasma/serum and donor segments follow Immediate Spin Crossmatch procedure.
9. Post incubation centrifuge gel card for 10 minutes.
10. Read and record results.

Interpretation

1. The presence of agglutination/hemolysis may indicate the presence of a serologically incompatible crossmatch. This result is interpreted as “incompatible”. The cause of all positive results must be investigated before transfusion.
2. The absence of agglutination/hemolysis is a negative result and indicates a serologically compatible crossmatch This result is interpreted as “compatible”.
3. Calculating the number of units to be tested when a patient has an antibody: Example: Patient has anti-K, require 2 compatible units

• • Use the negative frequency of the Ag (9% have “K” Ag therefore 91% do not have “K” Ag-negative frequency is 0.91)
  • Need 2 units. Divide the number of units required by the negative frequency for the antigen: 2/.91=2.2 (3) units need to be screened to get 2 compatible units
  • For multiple Ab’s: Multiply negative frequencies for ALL Ag’s and divide the number of units required by this combined frequency

Notes

1. The antihuman globulin test is sensitive to delays in testing. It is not permissible to interrupt or delay the test outside of manufacturers recommendations.
2. The antihuman globulin crossmatch will not detect errors in Rh typing, prevent iso-immunization of the recipient or ensure normal red blood cell survival.