title: Difficulties in Immunohaematology : The Weak D Antigen.
abstract: BACKGROUND
  The Rh blood system is one of the most polymorphic and immunogenic systems known to humans. The expression of Rh blood group antigen is complex. The Rh D antigen is the most important of the antigens that constitute the Rh antigen system. In most cases, D antigen can easily be detected. However, due to variability of expression, weak forms antigen are encountered. The reactivity of weak D with antisera is variable and presents as a problem in blood banking.
  
  
  METHODS
  A retrospective analysis for a five-year period was done. Blood samples that were negative for Rh D by immediate spin tube method were tested for weak D antigen by additional lab tests.
  
  
  RESULTS
  Of 34932 serial Rh grouping tests done in our Blood Bank, the incidence of weak D Rh antigen was 0.189%. All these were confirmed by the antiglobulin test.
  
  
  CONCLUSIONS
  These patients present as a problem for the blood banker and a curiosity to the clinician. Although uncommon, all health care workers should be aware of this entity to avoid anti D alloimmunisation.
authors.affiliation: Associate Professor, Department of Transfusion Medicine, AFMC, Pune.
authors.forename: H
authors.initials: H
authors.lastname: Kumar
authors.affiliation: Classified Specialist (Pathology and Haematology), AHDC(R&R), Delhi Cantt.
authors.forename: D K
authors.initials: DK
authors.lastname: Mishra
authors.affiliation: Cl Spl (Path & Haem) MH Roorkee.
authors.forename: R S
authors.initials: RS
authors.lastname: Sarkar
authors.affiliation: Professor and Head, Department of Transfusion Medicine, AFMC, Pune.
authors.forename: M
authors.initials: M
authors.lastname: Jaiprakash
keywords: Rh Blood Group; Weak D