ROS can be measured both directly and indirectly. Chemiluminescence is probably the most common way to directly measure ROS in sperm currently and can quantify both intracellular and extracellular ROS. It uses a luminometer in conjunction with a chemiluminescent probe such as luminol, which can also be used to measure a total antioxidant capacity (TAC). The results can be expressed as a ROS-TAC score, which can give an indication of the combined oxidant and antioxidant activities of seminal constituents. Unfortunately, this test requires special equipment, training, and is costly for widespread clinical use.
Due to these limitations, nitroblue tetrazolium (NBT) has been put forth as a cost-effective alternative. NBT interacts with free radicals and is converted to a blue pigment that can then be measured with light microscopy. This test suffers from a lack of standardization and low inter- and intra-observer reliability.
The new MiOXSYS Analyzer (figure 2) used at our institution measures the so-called oxidation-reduction potential (ORP). ORP measures the balance of all oxidants and antioxidants in the specimen and gives a complete picture of the oxidative stress. This test can be performed in less than 5 minutes. It requires no specialized training and may possibly replace the more complex and traditional oxidative stress tests without sacrificing the reliability. Elevated ORP levels correlate well with infertility, with a significantly higher ORP seen in infertile patients than in fertile controls.
In a recent study, ORP was able to detect at least one abnormal sperm parameter with a sensitivity of 70.4% and a specificity of 88.1%. It had an 88% sensitivity and 91.2% specificity when detecting oligozoospermia (Urology 2017; 104:84-89). Given the increased recognition that oxidative stress plays an important role in male infertility, development of reproducible and cost-effective techniques in measuring oxidative stress may help in tailoring our treatments for infertile couples.