Abstract

Paroxysmal Nocturnal Hemoglobinuria (PNH) is an acquired clonal stem cell disorder characterized by intravascular hemolysis due to GPI-deficient red blood cells sensitive to complement-mediated lysis. Accurate and sensitive detection of PNH-type cells has become important not only to diagnose PNH but also because studies have shown PNH-type cells may indicate favorable response to therapy and favorable prognosis in patients with aplastic anemia and myelodysplastic syndrome. Previous studies have suggested optimal testing for PNH-type cells by flow cytometry should be limited to within 48 hours after collection of whole blood. Our laboratory has developed a very sensitive and specific high resolution flow cytometric method for detecting PNH-type cells based on testing over 3,000 patients with known PNH, aplastic anemia, myelodysplastic syndromes and other bone marrow failure syndromes. The aim for this study was to determine the longevity of PNH clones in whole blood samples, the day-to-day variability of these clones and the rate of deterioration of the PNH clones compared to normal blood cells. We analyzed 10 whole blood samples from patients known to have PNH-type cells on seven consecutive days utilizing a two-color assay with GPA-CD59 for the red blood cells, a 5-color assay with FLAER-CD24-CD14-CD15-CD45 for the granulocytes and a 5 color assay with FLAER-CD33-CD14-CD64-CD45 for the monocytes. The results are summarized in the table below. The initial PNH clone sizes ranged from 0.02% to 90.8%. The PNH cells showed an overall similar level of deterioration to the normal blood cells with even minor PNH clones of 0.02% able to be detected at day 7. The day-to-day variability of PNH clone sizes was generally less than 10%, with smaller clone sizes showing a higher degree of variation, up to 20%, due to their smaller absolute numbers. Interestingly, Type III PNH red blood cells showed slightly better overall survival than normal red blood cells and were detected in modestly increasing percentages throughout the study. Based on this data, we propose that accurate detection of PNH type cells can be achieved up to seven days after collection of whole blood when utilizing high resolution flow cytometry. PNH Clone Size on Sequential Days as Percentage of Original PNH Clone Size

 Original PNH Clone Sizes PNH Clone Sizes as Percentage of Original PNH Clone Size 
Cell Type Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 
Type III RBCs .02%–58.6% 102% 106% 107% 104% 108% 103% 
Granulocytes .29%–90.8% 100% 100% 93% 89% 79% 86% 
Monocytes .52%–89.9% 96% 96% 92% 94% 97% 85% 
 Original PNH Clone Sizes PNH Clone Sizes as Percentage of Original PNH Clone Size 
Cell Type Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 
Type III RBCs .02%–58.6% 102% 106% 107% 104% 108% 103% 
Granulocytes .29%–90.8% 100% 100% 93% 89% 79% 86% 
Monocytes .52%–89.9% 96% 96% 92% 94% 97% 85% 

Disclosures: No relevant conflicts of interest to declare.

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