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. Du testing).
Policy:
- 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.
- Weak-D females of child-bearing ages (<50) should receive D-negative RBCs.
- 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