Abdul Muqtadir Abbasi: PNH – How to Interpret Flow Cytometry
Abdul Muqtadir Abbasi, Assistant Consultant at King Faisal Specialist Hospital and Research Center, shared a post on X:
“PNH: How to Interpret Flow Cytometry
PNH is diagnosed by demonstrating blood cells that lack GPI-anchored proteins due to an acquired PIGA mutation.
Which cells do we test?
- Neutrophils: FLAER and CD24
- Monocytes: FLAER and CD14
- RBCs: CD59, usually with CD235a to identify red cells
FLAER binds to GPI anchors. PNH cells have reduced or absent binding, while GPI-deficient cells show reduced expression of the relevant GPI-linked markers. What does “70% PNH clone” mean?
If 70% of neutrophils show GPI-anchor deficiency, the granulocyte PNH clone is 70%.
In simple terms, 70% of the tested neutrophils belong to the PNH population. Why test both neutrophils and monocytes?
The clone sizes are usually broadly concordant. Testing both myeloid lineages strengthens the diagnosis and helps quantify the clone.
Their results are generally more reliable for estimating clone size than RBC testing because PNH red cells are selectively destroyed by complement. Why can the RBC clone be smaller?
PNH RBCs lack CD55/CD59 protection and are vulnerable to complement-mediated hemolysis. Transfused normal RBCs can also dilute the measured RBC clone.
Therefore, a patient may have a 70% granulocyte clone but a much smaller RBC clone.
What are RBC Type I, II and III?
- Type I: Normal CD59 expression
- Type II: Partial CD59 deficiency
- Type III: Complete CD59 deficiency
Type III RBCs are generally the most susceptible to complement-mediated hemolysis.
Clinical pearls Use high-sensitivity flow cytometry to detect small clones. Test granulocytes and monocytes, alongside RBCs when appropriate.
A negative or very small RBC clone does NOT exclude PNH.
Clone size alone does not determine disease severity or the need for complement inhibition.
Remember:
PNH flow cytometry identifies GPI-anchor-deficient cells. Interpret the clone alongside hemolysis, thrombosis, cytopenias and the clinical picture.”
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