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EXERCISE 5

DuTest(Tube Method)

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Ing antigen only

PRINCIPLES AND APPLICATION:

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 antihuman globulin test is

necessary to identify patients with the Weak

D (formerly known as Du )phenotype. Weak D

testing is done on all prenatal patients andcandidates for Rh immune globulin.

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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 Dpositive patients should receive Rh positive

blood.

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OBJECTIVES:

a. Explain the importance of Du testing

b. Differentiate Du from the Rh antigens

MATERIALS:

Test tubes, rack and brush AHG

Dropper Anti-D or Anti-Rho

Syringe NSS(0.90%)

Antiseptic Bovine albumin 22%

Cotton Waterbath

Centrifuge machine

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PROCEDURE:

1. 2 test tubes (label-test and control)

2. Add anti-D in the test and Bovine albumin

for the control

3. Add 2 drops 3% Rh suspension on both

tubes

4. MCRO

5. Incubate the tubes at 37C for 15 min.

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6.Wash the red cell for 3x with NSS

7.Add 2 drops of AHG

8.Shake and mix well

9.Centrifuge for 15 sec. @ 3400rpm

10.Resuspend

11.Observe for the presence or absence of

agglutination

12.Record the result.

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GUIDE QUESTIONS:

1. What is Du?

Du is the weak expression of D antigen. Du

originally defined those red cells reacting

with anti-D only when a more sensitive

indirect antihuman globulin test was used.

But with the use of more potent anti-sera

(monoclonal reagents certain previously Dulabeled now classified as D-positive.

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2. How does Du differ with Rh antigens and antigenic

variants?

-The weak D phenotype (Du) is a weakened form of the

D antigen that in routine D typing will react with some

anti-D but not with others (when an immediate spin or37 incubation is done).

-Weak D red cells have the D antigen, but have fewer D

antigens per cell than normal Rh positive cells.

-The genetically transmissible Du is more common in

blacks and is transmitted in Mendelian dominant

pattern of inheritance.

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3 Mechanism for weak D:

1. Genetic/Inherited Weakened Expression

2. Position effect

- C trans-position effect

- Dce/dCe

3. Partial D

- absence of a portion or portions of the

total material that comprises the Dantigen.

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3. Name the Rh antigens and antigenic variants.

Rh Antigens: Rh antigen Variants

-D - Enhance D antigens

-c - Weak D(Du)-E - Del

-C - Rhnull and Rhmod

-e

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4.What is the clinical significance of Du factor?

The clinical significance of weak D is that

transfusion of such red cells to a Rh D immunized

subject can result in a haemolytic transfusion

reaction. If Weak-D red cells are transfused to a

Rh negative subject it may lead to

alloimmunisation to the Rh D antigen.

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-It is important that the Du status of the D negative

pregnant woman be established early in pregnancy.

-If the mother is found to be Rh positive, Du variant,

she is not a candidate for Rh immunoglobulin

prophylaxis- either ante partum or postpartum-

whereas the Rh negative (D and Du negative) mother

is a candidate.

-The reason for performing the Du test early in

pregnancy is to avoid misinterpreting the cause of apositive fetal cell screening test at the time of

delivery.

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5. What are the general rules to follow for Du

positive individuals, if they are recipients ofblood transfusion? If they are blood donors?

-Weak D as a blood donor:

As donors, weak D red cells are considered

to be Rh(D)-positive because, even though the Dantigen is weak, it is present. If weak D red cells

were transfused to D-negative patients, the

patients might be immunized to produce anti-D.

Some blood transfusion services give weak Ddonors the designation "Rh positive, weak D."

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Weak D as a blood recipient:As recipients, patients with the weak D

phenotype are considered to be Rh(D)-

negative, and usually receive only Rh(D)-

negative red cells. This is because a mosaic-

type weak D such as DAB might produce anti-D

(anti-DCD) if given DABCD red cells from a

normal Rh(D)-positive donor (although this is

unlikely). Note: If a weak D person phenotypes

as Rh(D)-positive, Rh(D)positive donor cells

would be transfused.