**4. Post-analytical phase and assay validation**

The results of PNH testing by flow cytometry are usually reported as percentage of type II and III PNH cells from the total gated neutrophils, monocytes and red blood cells. Assays reporting numeric data are considered as semi-quantitative, therefore the post-analytical validation process should comprise confirmation of accuracy, specificity, sensitivity, repeatability, reproducibility and stability [24, 25].
