Screening

Grouping

Antibody ID

SCREENING

There are a number of red cell antigens other than Rh and ABO which trigger antibody production and the clinically relevant antigens are represented on screening cells.
At RNSH Serum from the patient is reacted with these screening cells in Diamed gel cards and if a reaction is observed the specificity of the antibody is investigated.

It is important, prior to use of a specimen for screening to check that the sample is valid (if the patient has had a transfusion in the last three months a specimen is only valid for 72 hours). If the specimen is not valid a new specimen should be obtained as an antibody may have been produced.

Following a negative screen for antibodies, blood can be allocated to a patient if no reaction is observed in an immediate-spin crossmatch.

Auto controls: This control is designed to investigate whether if the patient's serum agglutinates the patient's own cells. This is run in parallel with the screen and is for detection of red cell autoantibodies. A postive autocontrol may indicate a positive direct antiglobulin test.

ANTIBODY SCREENING USING GEL CARDS

Principle
The polyspecific antibody screening cassettes contain rabbit antibody to human IgG, C3b/c and C3d. The reagent contains a buffer solution with bovine albumin, sodium azide and macromolecules. The reagent is coloured blue. One cassette will accommodate two separate patient antibody screens. It is acceptable to only use one half of the cassette provided that the remaining half remains totally sealed. A weak anti-D control is often used as a system control.

- Patient's serum
- 0.8% screening panel
- DiaMed Card One card for two (2) patient samples
- Micropipette and disposable tips
- Incubation chamber
- DiaMed system centrifuge

Procedure

1. Label the cassette with the patient's name or first 3 letters.
2. Check that the contents of the chambers are combined.
3. Incubate in the DiaMed incubator for 15 minutes.
4. Centrifuge the cassette using the DiaMed centrifuge.
5. Read the front and back of the individual columns for agglutination.
6. Record results in the computer system and on the request form.

*Interpretation of results* A positive reaction {score 3 (1+w); 5 (1+); 8 (2+); 10 (3+); 12 (4+)} is recorded when red cells are retained in or above the gel column after centrifugation. A negative reaction is recorded (as 0) when a distinct button of cells sediment to the bottom of the column after centrifugation. Haemolysis is recorded as a positive reaction. Reading and interpretation of results is done only on initial spin and performed within 30 minutes of centrifugation. If an IgM antibody causes stable agglutination at 37°C screen both IgM and IgG antibodies can be detected.	Click on image for high resolution view

	Left, Pt.1, No antibody detected Right, Pt.2 Antibody detected with Screening cell 1

Specimen preparation

Clotted specimens or specimens in EDTA, can be tested up to 7 days (specimens in heparin or sodium citrate can also be tested but these anticoagulants are not preferred).