The Rh Blood Group System Weak & Partial D

• RHD and RHCE genes are in close proximity on chromosome 1
• The complete deletion of the RHD gene could explain why D antigen is very potent in D negative people
• Five principle antigens (D, C, E, c, e) are responsible for the major ity of Rh incompatibilities
• Most D-positive red cells have a conventional RhD protein, but there are 70 different variants of D
• People can inherit D from both parents, or on D, or none. They can also inherit a variant and a normal, or 2 variants
• Weak D

  • formerly called Du
  • a mutation results in reduced number of D antigens on the red cell surface
  • can be detected using IAT
• Partial D

  • a situation where people type as Rh positive, but yet they make an anti-D antibody when alloimmunized
  • The D antigens are missing a piece of the gene
  • it was determined to be a situation where there is a replacement of part of the RHD gene with part of the RHCE gene
  • so it can turn out be a totally different piece
  • partial D is hard to assess unless there is also alloanti-D
• Testing for weak D is not required unless

  • testing an infant to determine if a Rh-neg mother needs RhoGam
  • Testing mother before she gives birth to see if she is really Rh-neg or not
  • some labs routinely do weak D testing on women of childbearing age who appear to be Rh-negative
• Donor Blood and Weak D

  • The Rh-negative donor gets tested by IAT - we don't want to give weak D positive blood to a Rh-negative patient
• Don't do IAT on recipient - just call them negative, they will get Rh-negative blood; do not want chance of partial-D person who might react with part of antigen they are missing
• Deleted/Partially deleted phenotypes

  • the problem is that when you transfuse them, they make antibodies to antigens (C, c, E, e) which are on everyone's red cells
  • must transfused them with D--/D-- blood
  • They are counseled to donate autologously, if posible
  • this can cause severe or fatal HDFN
• Anti-G

  • anti-G is an antibody formed in almost all cases of D-negative, G-negative patients with the genotype rr (dce)
  • The classic manner that anti-G is seen in a D-negative patient who has never been knowingly exposed to Rh-positive blood, yet presents with antibody that looks like a combination of both anti-D and anti-C (sometimes called anti-CD)
  • this antibody can be induced either by pregnancy or transfusion
• anti-G

  • give Rh-neg, G-pos blood to an Rh-neg, G-neg and they make an anti-G which will look like anti-C
  • from now one, this patient will need to get D-neg, C-neg lbood
• anti-G and pregnancy

  • when a D-neg mother has antibodies that look like anti-D along with anti-C in the antibody screen that is a routine part of prenatal care, the lab must ask a very important question: is this truly anti-D
  • if she really is making anti-D, she is not a RhoGam candidate, too late
  • if she is making anti-G, and not anti-D, she needs RhoGam to prevent her from making real anti-D
• Is it anti-G or anti-D and anti-C

  • done at reference lab
  • requires double adsorptions and elutions
  • pregnant women who is Rh-neg and shows up with anti-D and anti-C in her plasma needs to have her blood sent to reference lab
• Rhnull

  • Rhnull cells carry no Rh system antigens
  • very rare
  • RHD and RHCE are inactive
  • Can only get Rhnull blood
  • usually recommend autologous donation
• antigenicity

  • 30-80% of Rh negative people will develop anti-D following exposure to D-positive cells
  • you should only give Rh-positive blood to Rh-negative patient in emergencies
  • Rh-negative women and girls should always be given Rh-negative blood