I prepared this policy for HMC Qatar, which did not perform genotyping.

Principle:

Weakened expression of the D antigen may be due to either quantitative or qualitative defects.  Qualitative defects (partial or mosaic D) are uncommon.

Patients with quantitative defects have the whole D molecule and will not make anti-D upon exposure to D-positive RBCs.

Patients with partial or mosaic D may form antibodies against the portion of the D molecule they lack.  However, not all partial D types may make anti-D upon exposure.  Since we cannot specifically test for this condition, we shall consider females of child-bearing age with weak D as potentially partial D and use D-negative RBCs.

Genotyping for the D gene may define better which partial D types need to receive RhIG or D-negative transfusions.

Definition:

Weak D is defined as weak (1+ or weaker) reactions with one or more routine reagents or reactions only at antiglobulin phase (i.e. D^u testing).

Policy:

1. All donor units must be tested by a method to detect weak D phenotype.  If such testing is positive, the donor unit must be labelled as D-positive and be used routinely for D-positive patients.
2. Weak-D females of child-bearing ages (<50) should receive D-negative RBCs.
3. Weak-D males may receive D-positive RBCs unless they are a potential recipient of chronic transfusions (e.g. thalassemia, sickle cell disease, etc.)

References:

Technical Manual, Current Edition, American Association of Blood Banks, Bethesda, Maryland, USA

Standards for Blood Banks and Transfusion Services, Current Edition, AABB, Bethesda, MD, USA