A Flow Cytometer is the highly technical instrument needed for the SCSA® test. The key to the development of the SCSA test was the invention of the flow cytometer. Dr.Evenson was a faculty member in the Cytometry lab at the Memorial Sloan Kettering Cancer Center, New York City, which was one of several labs that are credited with the invention of this instrument in the late 1960s. In essence, the flow cytometer rapidly measures (250 sperm /sec) with high precision ("machine vision", rather than the human eye with a light microscope) thereby giving a statistically robust result based on data from 5000 sperm per sample. The precision of flow cytometry, coupled with the precision biochemistry of the SCSA test, provides unparalleled measures of sperm chromatin and DNA integrity.
The essence of a flow cytometer is that cells are stained with a fluorescent DNA dye (acridine orange) and then forced through a glass channel in a liquid suspension. When the cells pass through the focal point of the laser beam, the laser light will cause the dye to emit fluorescent light of a certain color.
For the SCSA® test, green fluorescing sperm have non-detectable levels of fragmented DNA, while yellow to red fluorescing sperm have moderate to high levels of fragmented DNA, respectively. Moderate to high DNA fragmentation levels found within these red fluorescing sperm are likely beyond the DNA repair capacity of the egg. Measurements from 5000 individual sperm are analyzed by the SCSAsoft software to determine the percentage of the sperm with increased yellow to red color (% DFI), and the % of sperm with nuclear immaturity (% HDS)