what is weak D
D antigen present on RBC but expressed v weakly
not react strongly in routine Rh typing
[as it is weak, laboratories sometimes need a special test (Weak D test) to detect it]
briefly explain the causes of weak D
- Genetic Weak D
- D antigen is normal but produced in small amt on RBC surface
- as genes inherited from parents, which affect how much D antigen is expressed
[few D antigens → weak reaction in testing] - C-trans (Position Effect)
- C-antigen gene sits opposite the D gene = reduced the expression of the D antigen
- when C is opposite (trans) t D, it interfered with D antigen expression
example:
Dce / dCe
DcE / dCE
- Partial D (Mosaic D)
- D antigen is incomplete
- instead of being weak, some parts of the antigen are missing
*D antigen is made of many small parts called epitopes. in partial D, some epitopes are missing
= not fully developed, person can form antibodies against missing parts of D
*clinically impt in blood trnsfusion and pregnancy
interpret the following:
1. Dce / dCe
2. DCe / dce
- Weak D (C in trans reduces D expression)
- Normal D (no C opposing D)
[as C is big (strong antigen), it reduces the expression of D, making D appear weak]
why are epitopes important in partial D
as D antigen is made of many small parts called epitopes
[each small piece = epitope
whole puzzle = the complete D antigen]
so, in partial D, some puzzle pieces (epitopes) are missing = antigen is incomplete
this is the main antigen to determine the Rh blood type
D antigen
Rh+
- D antigen is present on RBCs
- agglutination occurs
Rh−
- D antigen is absent on RBCs
- no agglutination
this test is done to confirm negative Rh typing results
weak D determination
- to check if the person actually has a weak form of the D antigen
[sometimes the D antigen is present but very weak, so it does not react in the first Rh test. so the lab performs a Weak D test using Anti-Human Globulin (AHG) to confirm]
true or false:
It is plausible to immediately report Rh negative without confirming Weak D.
false - do NOT
what is used for the following in Weak D testing
specimen:
reagent:
cells used:
Specimen:
- negative result from the Rh typing
Reagent:
- anti-human globulin (AHG)
Cells used:
- 5% Red Cell Suspension (RCS)
procedure in weak D determination
- mix pateint RBC and anti-D reagent
- centrifuge
- check reaction
Rh+ = agglutination occurs
Rh− = no agglutination
*if no agglutination, procced to Indirect Antihuman Globulin Test (IAT) using AHG
[to help detect v small amt of D antigen]
interpretation result after Weak D test using AHG: Indirect Antihuman Globulin Test (IAT)
agglutination with AHG:
weak D Positive → Rh Positive
no agglutination with AHG:
true Rh Negative
are asians/ filipinos usually Rh positive or negative
Rh positive
- however, there are genes that secrete without Rh antigen
- do not release Rh negative without weak D determination
what are the manner of reporting in AHG Test for Weak D
DU reaction:
(0) No agglutination
Manner of reporting:
Dᵘ negative
DU reaction:
(+) With agglutination
Manner of reporting:
Dᵘ positive
manner of reporting when negative reaction confirms that the person is Rh negative (Patient or donor)
Rh (-), Dᵘ (-)
manner of reporting when initial Rh test looked negative but Weak D test became positive
Rh (-), Dᵘ (+)
REPORT IF PATIENT/ DONOR
Patient → treat as Rh NEGATIVE
Donor → classify as Rh POSITIVE
Why is classification different for patients and donors?
Patient
- Rh Negative
- To prevent formation of anti-D antibodies
[even if they have weak D, their immune system might still react to strong D antigens from transfused blood = given Rh negative blood to stay safe]
Donor
- Rh Positive
- Their RBCs still have D antigen that could affect recipients
[their blood were given to a true Rh-negative patient, it could cause the patient to develop anti-D antibodies = donors with Weak D are labeled Rh positive]
[patient = -ve = avoid anti-D formation
donor = Rh positive = RBCs contain D antigen]
this test is done when the initial Rh typing shows no agglutination to check if the person has Weak D (Du antigen).
AHG Test for Weak D (IAT)
- Indirect Antihuman Globulin Test
procedure in Indirect Antihuman Globulin Test
- Initial Rh typing
mix patient RBC + Anti-D
centrifuge
*if no agglutination
proceed to Weak D test
- Weak D testing steps
incubate at 37 °C
wash RBCs 3 times (to remove unbound antibodies)
add 2 drops of AHG reagent
centrifuge and observe for agglutination
