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