Final answer:
The Speech Reception Threshold (SRT) test is likely being referred to when starting a hearing test at 15 to 20 dB over the PTA, as it measures the threshold where speech is understood 50% of the time.
Step-by-step explanation:
When a hearing test starts at 15 to 20 dB over the patient's Pure Tone Average (PTA), the test that is most likely being conducted is the Speech Reception Threshold (SRT) test. The SRT test is used to identify the lowest level at which speech can not only be detected but also understood 50% of the time. This test is crucial for determining the degree of hearing loss and aids in fitting hearing aids and other assistive listening devices. In contrast, the UCL (Uncomfortable Loudness Level) measures the level at which sound becomes uncomfortably loud for the listener, while the MCL (Most Comfortable Loudness) identifies a level where speech is most comfortably heard. The SDT (Speech Detection Threshold) is similar to the SRT but only measures the level at which speech is detected, not necessarily understood.