Sensitive Flow Cytometry Assays for PNHPNH* is an acquired stem cell disorder that affects all blood cells. Clinical symptoms include hemolytic anemia, venous thrombosis and diminished production of blood cells. In PNH, a somatic mutation results in the absence of a number of proteins normally found on the cell surface. Cells missing these proteins, termed GPI-APs**, are detected in the laboratory by flow cytometry.
Two Flow Cytometry Tests for PNH Diagnosis The International PNH Interest Group recommends that PNH testing be done on 2 cell lineages using 2 different markers. Accordingly, BloodCenter of Wisconsin’s Platelet and Neutrophil Immunology Laboratory offers 2 tests. The first test detects PNH red blood cells using the marker CD59, and the second test detects PNH white blood cells using the marker FLAER.
The red blood cell test is a sensitive indicator of whether a patient has PNH or not. Only the red blood cell test allows estimation of the proportion of the 3 types of PNH red blood cells. Knowing both the proportion and type of PNH red blood cells supports clinical management of the anemia.
The white blood cell test gives an accurate estimate of clone size, which helps determine if treatment is needed. That is, the white blood cell test results give a better indication of when treatment is needed, and how well treatment is working when it’s given. (A limitation of the white blood cell test is that it must be performed within 48 hours of sample collection.)
Suggested Testing Algorithms For a new patient being evaluated for PNH, the physician could order the red cell test to begin with, and then follow up with white blood cell testing if the initial test is positive. This would be a good way to test if the clinical suspicion is low to moderate. If the suspicion is high, order both tests at the same time. (Both tests can be performed on the same blood sample.)
For established cases of PNH being treated or monitored for disease activity, ordering the white blood cell test alone should provide sufficient information.
*PNH: Paroxysmal Nocturnal Hemoglobinuria |
