What does ATP testing measure to indicate the presence of living cells?

ATP testing is a method used to assess the presence of living cells by measuring the amount of adenosine triphosphate (ATP), which is a molecule found in all living cells and is essential for energy transfer within them. The testing works on the principle that when ATP comes into contact with specific reagents, a biochemical reaction occurs that produces light. The intensity of this light is directly proportional to the amount of ATP present, allowing us to gauge the level of biological contamination on surfaces.

This makes the measurement of light produced by ATP molecules the most effective and relevant method for indicating the presence of living cells. Other options, such as temperature changes, pressure levels, and water content in the air, do not provide a direct indication of the presence of living cells and are therefore unrelated to ATP testing.