Fluorescein-labeled proaerolysin (FLAER) is a flow cytometric assay used to diagnose paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria , sometimes referred to as Marchiafava-Micheli syndrome, is a rare, acquired, potentially life-threatening disease of the blood characterised by complement-induced intravascular hemolytic anemia , red urine and thrombosis...

 (PNH). The assay takes advantage of the action of proaerolysin, a prototoxin of aerolysin

Aerolysin

In molecular biology, aerolysin is a cytolytic toxin exported by Aeromonas hydrophila, a Gram-negative bacterium associated with diarrhoeal diseases and deep wound infections. The mature toxin binds to eukaryotic cells and aggregates to form holes leading to the destruction of the membrane...

, a virulence factor of the bacterium Aeromonas hydrophila

Aeromonas hydrophila

Aeromonas hydrophila is a heterotrophic, Gram-negative, rod shaped bacterium, mainly found in areas with a warm climate. This bacterium can also be found in fresh, salt, marine, estuarine, chlorinated, and un-chlorinated water. Aeromonas hydrophila can survive in aerobic and anaerobic...

. Proaerolysin binds to the glycophosphatidylinositol

Glycophosphatidylinositol

Glycosylphosphatidylinositol is a glycolipid that can be attached to the C-terminus of a protein during posttranslational modification...

(GPI) anchor in the plasma membrane of cells. Cells affected by PNH lack GPI anchoring proteins, and thus are not bound by proaerolysin. Of note, normal erythrocytes and platelets cannot be used to evaluate for expression of GPI anchoring proteins.