Uncommonly, D-positive people have significantly decreased quantities of the D antigen, so they do NOT test as D-positive with routine immediate spin testing (instead, positive reaction is only seen at the “AHG phase“). Such persons are defined as “weak D” (formerly “Du“).
Is Weak D positive or negative?
An individual with weak D has a decreased amount of D antigens expressed on the red cell. With current serologic testing, most individuals with weak D are typed as Rh-positive via direct agglutination testing using anti-D.
What does weak D negative mean?
Weak D as a blood donor: As donors, weak D red cells are considered to be Rh(D)-positive because, even though the D antigen is weak, it is present. Weak D as it relates to prenatal testing: An Rh(D)-negative woman is given Rh immune globulin if she has an Rh(D)-positive infant and has not produced active anti-D.
When should a weak D test be performed?
1.2 Testing for weak D shall be performed in the case of an Rh negative neonate (less than 4 months of age) of an Rh negative mother with no evidence of Rh alloimmunization. 1.3 Weak D shall be performed if there is a discrepancy in previous and current results obtained with the Rh anti-sera.
How common is weak D?
Approximately 0.2% to 1% of routine RhD blood typings result in a “serological weak D phenotype.” For more than 50 years, serological weak D phenotypes have been managed by policies to protect RhD-negative women of child-bearing potential from exposure to weak D antigens.
Are blood donors tested for weak D?
Today, weak D antiglobulin testing is required for blood donors and newborns of D negative mothers to detect potentially immunogenic weak D red blood cells. Weak D typing is not required, nor encouraged, for transfusion recipients and pregnant women.
How can you tell a weak D?
The way to detect weak D cells reliably is to do a test for weak D (usually called a Du test). The Du test is an indirect antiglobulin test using the patient’s red cells and an IgG anti-D. An IgG anti-D must be used because antiglobulin serum contains anti-IgG.
What is a characteristic of a person who is weak D?
What is the characteristic of a person who is weak D? Demonstrates a reduced number of D antigen sites on the surface of the red cell.
What is weak D testing for?
The testing of weak D antigen is of particular importance in patients with chronic requirements for blood transfusion such as thalassemia, sickle cell anemia, chronic renal failure, HIV/AIDS. If these Rh D-negative individuals are found to be positive for weak D antigen, they can be transfused with Rh D-positive blood.
How do you know if you have a weak D?
In the UK, the recommended method for D typing of patients requires direct agglutination tests, in duplicate, with potent IgM monoclonal anti-D reagents. An antiglobulin test is not required. This means that very weak D red cells will be typed as D negative.
What is the importance of weak D testing?
The importance of weak D lies in the fact that it is much less antigenic as compared to Rh D and weak D red cells may be destroyed if transfused to a person having anti D. Hence, weak D donor units are currently labelled as Rh D positive. Weak D testing is not done for a recipient and they are labelled as Rh negative.
What is a weak D antigen?
Weak D antigen is a phenotype where the D antigen is weakly expressed on red blood cells, and this antigen cannot be detected by routine methods.
How do you test for weak D?
How do you test for weak D antigen?
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).
With current serologic testing, most individuals with weak D are typed as Rh-positive via direct agglutination testing using anti-D.
What is weak D blood type?
The weak D phenotype is a weakened form of D antigen that in routine D antigen testing will react with some anti-D but not with others (when 37 C incubation or an immediate spin is given). Weak D RBC has D antigen but fewer in number as compared to normal Rh D-positive red cells.
Who are routinely tested for weak D?
How do you perform a weak D test?
What does weak D stand for in medical terms?
The weak D (formerly D u) phenotype describes an individual with a variant RHD allele, leading to low expression of complete D antigen on the surface of their red blood cells.
What is the difference between weak D and partial D?
The weak D (formerly Du) phenotype describes an individual with a variant RHD allele, leading to low expression of complete D antigen on the surface of their red blood cells. The partial D phenotype describes a variant RHD allele that results in modification of the surface D antigen and can result in the loss of D epitope.
Why are red blood cells called weak D?
Historically, red blood cell antigens that react with anti-D only after extended testing with the indirect antiglobulin test are called weak D. Weak D expression primarily results from single point mutations in RHDwhich encode amino acid changes predicted to be intracellular or in the transmembrane regions of RhD.
What causes a person to have weak D?
Weak D phenotype most commonly results from a single point mutation in the transmembrane domain of the RHD gene. More than fifty different weak D types have been reported so far.
