Flow cytometry testing uses fluorescent reagent to diagnose PNH
Plainview, NY-based Acupath Laboratories Inc. now offers flow cytometry testing using the new FLAER reagent for paroxysmal nocturnal hemoglobinuria (PNH), an acquired genetic blood disorder that can cause thrombosis, end organ damage and increased mortality.
The fluorescent version of the protein aerolysin, FLAER selectively binds to all the GPI anchor proteins on the surface of all white blood cells. In testing at the National Institutes of Health, FLAER has been shown to more accurately and more specifically identify PNH clones. The absence of CD55 and CD59 on the red blood cells, and the absence of CD55, CD59 or other GPI anchor molecules and/or FLAER binding on the white blood cells (e.g., on granulocytes) define the presence of a PNH positive clone.
Dr. Zsuzsanna Vegh-Goyarts, Ph.D., co-director of flow cytometry and tumor markers for Acupath, explained that PNH is a hematopoietic stem cell disorder caused by a somatic mutation of a single gene. “This mutation may occur in PNH, as well as in aplastic anemia and myelodysplasia or Myelodysplastic syndrome (MDS), resulting in PNH-like clones. Patients with the defective gene have a partial or complete deficiency of the GPI anchor proteins—for example, CD55 and CD59—that are protecting cells from lysis,” she explains. “These proteins are lost in PNH clones that causes the lysis of the red blood cells in PNH patients. The loss of these cell surface molecules is detectable by flow cytometry." Traditionally, the red blood cell CD55 and CD59 were the diagnostic targets; however, testing only the red blood cells will lead to false negative results since they are sensitive to lysis and may not be detectable. “The second lineage of choice for testing is the granulocytes. One can test for CD55 and CD59 on the granulocytes as well, but research in recent years led to a more specific reagent—FLAER,” she explains.
One reason that doctors are using newer, more accurate tests for PNH recently is the launch of a new drug therapy, Soliris, which was approved by the FDA in 2007 and is extremely effective at treating symptoms of PNH. The drug works by blocking the reaction that causes hemoplysis. Additional treatments may include bone marrow transplant, transfusions and steroids. Follow-up of patients during and after treatment with the sensitive FLAER reagent has a great advantage over traditional PNH testing methods.
PNH affects 8,000-10,000 people in North America and Europe, typically striking men and women in their early 30s. It develops without warning and, because it is so rare, PNH often goes unrecognized, with delays in diagnosis ranging from one to more than 10 years. PNH patients tend to survive 10-15 years from the time they are diagnosed.
Posted by Lee Mather
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