Tareq Abadl: Not Every Rh-Positive or Rh-Negative Result is That Simple
Tareq Abadl, Medical Lab Specialist, shared a post on LinkedIn:
“Not every ‘Rh-Positive’ or ‘Rh-Negative’ result is that simple!
Most people think RhD typing is a clear yes or no — but in transfusion medicine, it’s not always that straightforward.
Some individuals have what’s called a weak D or other RHD variants.
This means the D antigen is present, but expressed at very low levels, structurally altered or reacts inconsistently in routine testing.
Because of this, standard serologic typing may give uncertain or misleading results.
Why does this matter?
In blood banking, especially during pregnancy, this distinction is critical.
The American Red Cross notes that weak or altered D expression can produce a serologic weak D phenotype.
The AABB recommends molecular (genotyping) testing when RhD results are unclear.
Why? Because management decisions can change.
- Weak D types 1, 2, and 3 – can be safely treated as RhD-positive.
- Other variants (like partial D) – may still form anti-D – managed as RhD-negative
Key clinical impact this directly affects:
- Rh immune globulin (RhIg) use.
- Blood transfusion selection.
- Risk of alloimmunization.
Without genotyping, patients may: receive unnecessary RhIg or be given Rh-negative blood unnecessarily (a limited resource).
Even donor testing is more detailed than people expect: The Canadian Blood Services confirms that first-time donors typed as Rh-negative are often retested for weak D to ensure accurate classification.
Newer Insight (Important): Recent practice is shifting toward
- Routine RHD genotyping in pregnant patients with weak D.
- Better standardization of interpretation across labs.
- Reducing variation between hospitals in RhIg decisions.
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