Transcript Weak D
WEAK D TESTING (DU) Mr. Mohammed Jaber. WEAK EXPRESSION OF THE RHD ANTIGEN (DU) The term DU is widely used to describe cells which have a quantitative reduction in the expression of their RhD antigen. Or qualitative variation in RhD antigen expression, these are referred to as partial D. Weak D individuals may also be partial D. DU TEST SHOULD BE DONE IN THE FOLLOWING SITUATIONS: When weak or 1+ reactions are found. Microscopic readings should only be done if mixed field agglutination* is suspected. When Rh typing discrepancies are found between current and previous results. On Rh negative neonates born to Rh negative mothers. If the weak D testing is positive, the neonatal Rh type would be reported as "D positive" and the mother would be a candidate for Rh Immune Globulin (RhIG). PRINCIPLE To test for a weak expression of the D antigen. Red cells that react weakly or not at all in direct agglutination tests with anti-D may react with anti-D by the indirect antiglobulin test (IAT). Red cells that fail to react 2+ in direct agglutination tests with anti-D are incubated with anti-D at 37° C and examined for agglutination. The red cells are washed to remove unbound antibody (IgG anti-D), then tested with anti-IgG. SPECIMENS Clotted or anticoagulated whole blood Reagents & Equipments 37oC incubator Wash bottle with normal saline Coombs serum - either polyspecific or anti-IgG Coombs control cells (IgG coated control cells ). All reagents, equipment, and supplies used in the Rh testing procedure RECOMMENDED TECHNIQUES 1. SLIDE TECHNIQUE 1.1 Add to a clean, labelled slide: • One drop of anti-D IgM & IgG blend. • One drop of the test red cells suspension. 1.2Mix well by gently and continuously rocking the slide for approx. 30 seconds and incubate the test for 5 minutes at room temperature, with occasional mixing. 1.3 Examine macroscopically for agglutination. A diffuse light source may aid reading. 2. TUBE TECHNIQUE – IMMEDIATE SPIN 2.1 Prepare a suspension of test washed red cells 2-3% or 1.5-2% in LISS. 2.2 Place in a small, labelled test tube: • 1 volume of anti-D IgM & IgG blend. • 1 volume of suspended red cells. 2.3 Mix well. 2.4 Centrifuge immediately for 10 seconds at 1000g or for a suitable alternative force and time. 2.5 Agitate the tube gently to dislodge the cell button and examine macroscopically for agglutination. Apparently negative tests which are to be tested for DU should be further tested by the DU test method. 3. TUBE TECHNIQUE – LISS 3.1 Place in a small, labelled test tube: • 1 volume of Anti-D blood grouping reagent • 1 volume of red cells suspended 1.5-2% in LISS. 3.2 Mix well and incubate for 15-20 minutes at 37°C. 3.3 Centrifuge immediately for 10 seconds at 1000g or for a suitable alternative force and time. 3.4 Agitate the tube gently to dislodge the cell button and examine macroscopically for agglutination. 4. DU TEST METHOD (INDIRECT ANTIGLOBULIN TEST (IAT). ) After reading the immediate spin results, re-incubate the test for a further 20 minutes at 37°C before completing the DU test method described below. OR After reading the LISS tube test, complete the DU test, without further incubation, following the procedure given below. DU TEST METHOD 4.1 Wash the test 4 times with a large excess of PBS (e.g. 4ml of PBS per 12 (or 10) x 75mm glass tubes). NOTE: a) allow adequate spin time to sediment the red cells b) make sure that most of the residual saline is removed at the end if each wash to leave a ‘dry’ cell button. 4.2 Add two drops of anti-human globulin reagent to each tube. 4.3 Mix thoroughly. DU TEST METHOD 4.4 Centrifuge at 1000g for 10 seconds or for a suitable alternative force and time. 4.5 Agitate the tube gently to dislodge the cell button and examine macroscopically for agglutination. 4.6 Add 1 drop of IgG-coated control cells to the tube(s) with negative results. Centrifuge, resuspend cells, read macroscopically and record results. Agglutination (2+) shall be present or the test shall be repeated. PROCEDURAL NOTES Tests should be read immediately after centrifugation. Delay may cause bound IgG to dissociate from red cells and either leave too little IgG to detect or neutralize AHG reagent causing false negative results. Interpretation A negative result in the immediate spin phase but agglutination in the D tube following incubation (with no agglutination in the DC tube) indicates a positive test for weak D. Lack of agglutination is a negative test and the patient is considered truly D negative. Agglutination in the DC tube invalidates the test.