Flow Cytometry Screening for Paroxysmal Nocturnal Hemoglobinuria Abnormal Clones in Saudi Arabia

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease with insidious process, chronic course and life-threatening condition. PNH is clinically defined by the deficiency of the endogenous glycosyl phosphatidylinositol (GPI)-anchored complement inhibitory protein. It has always aroused interest in the medical profession rendering screening and proper diagnosis by flow cytometry (FCM) technology a priority

We reviewed all samples submitted for PNH/ FCM screening for the past 2 years (2012-2013) at hematology section, Department of Pathology and Laboratory Medicine, King Faisal Specialist Hospital and Research Center (General Organization). We collected the positive cases and reviewed them for age, gender, indication for screening, sample type, size of the PNH clone and cell type affected. Immunophenotypic analysis was performed using gating antibodies CD45, CD15, CD33, CD235a GPI-linked antibodies, CD59, CD14, and CD24 as well as fluorescent Aerolysin (FLAER).

In a total of 366 peripheral blood samples submitted for PNH/ FCM screening fifteen samples (4%) were positive for PNH clones but only 12 patients were available for analysis. The median age for our patients was 34 years with approximately equal male to female distribution.

12 cases showed type II and III clones within the RBCs with clone size ranging between 0.04% and 56%. Analysis of granulocytes and monocytes revealed type III clone in 8 cases, type II and III clone in 3 cases and non in one case. The percentage of the clone varies between the granulocytes and monocytes and ranges from 1% up to 100%.

Of 12 positive PNH cases, 8 (66.7%) patients were diagnosed as having aplastic anemia (AA), 1 (8.3%) patient with Budd-Chiari syndrome, 1 (8.3%) patient has chronic immune thrombocytopenia (ITP), and 2 (16.7%) patients presented with pancytopenia.

This study confirms the rarity of the disease since only 4% of the submitted samples for analysis turned to be positive for PNH. The detection limit for a PNH clone by FCM in the RBC or WBC is 0.01%. Identification of small PNH clone is greater FCM sensitivity relative to old test used for the same purpose (Ham test). The use of the FLAER allowed us to detect granulocytic PNH clone, however, granulocytes PNH clone detection alone without RBCs clone detection is not recommended. This review confirms the previous percentage of positive cases (5.9%) reported from this center on a smaller number of cases during the past few years.