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The page below is a sample from the LabCE course Overview Of Major Antigens of the Rh Blood Group System. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Deletion, null and mod Phenotypes in the Rh System

Rare phenotypes have been identified that do not react when tested with anti-C, anti-E, anti-c, or anti-e. These individuals lack the genetic material or the functionality of it has been changed or silenced. This is referred to as a deletion phenotype. Many examples of deletion phenotypes have an unusually strong D antigen expression, frequently referred to as exalted D or elevated D. The deletion phenotype is indicated by the use of a dash (-) as in the examples that follow: DC- (DC dash) or Dc- (Dc dash), in which there is deletion of the E gene, or D-- (D dash dash), in which there is deletion of both C and E genes. The antibody potentially made by D--/D-- individuals is called anti-Rh17 or anti-Ho .
A variation within the deletion D-- is recognized and referred to as D .. (D dot dot). The D antigen in D.. is stronger than that in DC- or Dc- samples, but weaker than that of D-- samples. A low prevalence antigen called Evans (Rh:37) accompanies the Rh structure of D.. cells.
Another rare individual may lack all Rh antigen expression and is said to be Rhnull . Their phenotype is written ---/---. These individuals are said to have Rhnull syndrome and demonstrate a mild compensated hemolytic anemia, reticulocytosis, stomatocytosis, slightly to moderately low hemoglobin/hematocrit, increased hemoglobin F, decreased serum haptoglobin, and may have an elevated bilirubin level. The clinical condition of these patients is highly variable. When they require transfusion, Rhnull blood must be given.
Weakened expression of all Rh antigens has also been reported as a rare occurrence and those individuals are said to have the Rhmod phenotype. When describing this phenotype in written format, parentheses are used as in (D), (C), and (e) to indicate the weakened expression of the given antigen.
Harmening, DM,: Modern Blood Banking & Transfusion Practices, 6th ed. FA Davis, Philadelphia, PA, 2012, p 163.
Fung, MK, Eder, AF, Spitalnik, SL, Westhoff, CM (eds): Technical Manual, 19th ed. AABB, Bethesda, MD, 2017, p 311.