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Weak D Testing (Du) Testing Principle and Applications

Weak D testing identifies individuals with a weakly expressed D antigen through an indirect antiglobulin test. It is performed on all prenatal patients, Rh negative blood donors and transfusion candidates to ensure proper Rh immune globulin administration and compatible blood transfusions. The test involves incubating a patient's red blood cells, washing, adding anti-human globulin and checking for agglutination which would indicate a weak D positive result. A true weak D result will be at least 2+ positive while weaker reactions may be due to prior transfusions.

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1K views1 page

Weak D Testing (Du) Testing Principle and Applications

Weak D testing identifies individuals with a weakly expressed D antigen through an indirect antiglobulin test. It is performed on all prenatal patients, Rh negative blood donors and transfusion candidates to ensure proper Rh immune globulin administration and compatible blood transfusions. The test involves incubating a patient's red blood cells, washing, adding anti-human globulin and checking for agglutination which would indicate a weak D positive result. A true weak D result will be at least 2+ positive while weaker reactions may be due to prior transfusions.

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Mai Üü
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© © All Rights Reserved
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Weak D Testing (Du) Testing

PRINCIPLE AND APPLICATIONS


Some red cells possess the D antigen but it is expressed so weakly that the cells are not agglutinated
directly by anti-D sera. An indirect antiglobulin test is necessary to identify patients with the Weak D
(formerly known as Du )phenotype. Weak D testing is done on all prenatal patients and candidates for
Rh immune globulin. Weak D testing is also done on Rh negative donors to ensure they are truly D
negative. It may or may not be done routinely on Rh negative candidates for transfusion, depending on
the policy of the transfusing institution. If routine weak D testing is done, weak D positive patients
should receive Rh positive blood.

SAMPLE
Any sample satisfactory for ABO and Rh testing is acceptable. The weak D is most often performed
directly from the same tube set up for the Rh test, if the patient cells were a washed 3% suspension.

REAGENTS, EQUIPMENT, AND SUPPLIES


37degC incubator
Wash bottle with physiologic saline
Coombs serum - either polyspecific or anti-IgG
Coombs control cells
All reagents, equipment, and supplies used in the Rh TESTING procedure

PROCEDURE
- Prepare a washed, 3% suspension of patient cells, and set up the D and DC (Rh Control) tubes, if not
already done. (SEE ABO/Rh TYPING PROCEDURE)
- Record the D and DC immediate spin results. If the Rh test is negative, continue with step 3.
- Incubate both tubes at 37oC for 15 to 30 minutes.
- Centrifuge and read for agglutination as usual. If the Rh test is negative, continue with step 5.
- Wash both tubes 3-4 times with saline.
- Immediately after the last wash, add one drop Coombs serum to each tube and centrifuge in the
serofuge the time appropriate for the Coombs spin calibration.
- Immediately resuspend gently and examine for agglutination using the lighted agglutination viewer.
- Record results in the appropriate column on the worksheet
- Confirm all negative results by adding one drop Coombs control cells to all tubes showing no
agglutination and centrifuge 15-30 seconds at high speed in the serofuge.
- Gently resuspend and examine for agglutination. Agglutination should be present in this step or the
test is invalid.

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.

A true weak D should give at least a 2+ positive result. Weaker results may be due to mixed field
agglutination in an Rh negative individual who received Rh positive blood, or vice-versa. Obtain a recent
transfusion history on patients who give inconclusive weak D results

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