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Flow Cytometry

Flow Cytometry, the Standard Diagnostic Test for PNH1,2

Flow cytometry is a sophisticated laboratory technique used to identify and sort cells and their components. Flow cytometry is considered to be the standard diagnostic test for confirming PNH and in most cases has replaced the need for older tests including the Ham test or sucrose haemolysis test. Physicians can determine the exact proportion of PNH cells in your blood by using this technique.

Flow cytometry uses complex computerized instruments to pass a stream of single blood serum cells through a laser beam where they are labeled with a fluorescent dye and then analyzed. The test for PNH requires a small sample of the patient’s blood from a vein in the arm. It detects PNH blood cells by using either monoclonal antibodies or FLAER (fluorescent aerolysin). Monoclonal antibodies attach to the GPI-anchored proteins (such as CD59) attached to the surface of red blood cells. FLAER attaches to the GPI anchors themselves. Sometimes it takes multiple tests to come to an accurate result.

FLAER is becoming more and more popular because it is a highly sensitive test. It uses a fluorescenated bacterial protein that binds to the GPI anchor itself. Since it binds to the GPI anchor, it recognizes all proteins that are attached to the cell surface by this anchoring mechanism. Defective cells that are missing the GPI anchors and the protective proteins are characterized as PNH blood cells.

Also keep in mind that all commercial testing labs are different and each will have its own values for a positive PNH test.

PNH Quick Facts

PNH cannot be inherited from parents, nor can it be passed on to children.2


References: 1. Brodsky RA. Paroxysmal nocturnal haemoglobinuria. In: Hoffman R, Benz EJ Jr, Shattil SJ, et al, eds. Hematology: Basic Principles and Practice. 4th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2005:419-427. 2. Socié G, Mary J-Y, de Gramont A, et al, for the French Society of Haematology. Paroxysmal nocturnal haemoglobinuria: long-term follow-up and prognostic factors. Lancet. 1996;348:573-577.