The D (Rho) antigen was first identified in 1939 and is present on the erythrocytes of approximately 85% of the Caucasian population. Human red blood cells are classified as Rh positive or Rh negative based solely on the presence or absence of the D antigen. Anti-D serum is used for routine Rh determination, and the Du variant (weak D) is also tested in this procedure when needed.

Rh (D) typing is based on the principle of agglutination. Red blood cells that possess the D antigen will agglutinate when exposed to anti-D antibody.

• Agglutination with anti-D serum and no agglutination with the control reagent indicates a positive result (D antigen present).
• No agglutination indicates a negative result (D antigen not detectable).

If Rh typing is negative, Du (Weak D) testing is automatically performed.

Tubes containing serum separator gel (may cause false agglutination; will be rejected)

None required

Reported as Rh positive or Rh negative

• American Association of Blood Banks. Technical Manual, 9th ed. Arlington, VA: AABB; 1985.

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