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Pure tone audiometry is a hearing test. It is used to determine whether a person is suffering from hearing loss, and it can give results for each individual ear. Typically using a pair of headphones or earbuds that are inserted into the ear, both of which block any ambient sound in the room, the test determines the ability of the individual to hear a signal when passed through the air of the inner, outer and middle ear as well as through the bones of the skull.
Subjects who are not able to wear headphones, such as young children, can also be tested in a soundproof room with speakers instead of ear buds. Pure tone audiometry tests are typically given by an audiologist with a reference from an otolaryngologist, a doctor who specializes in the ear, head, neck, nose and throat. There are two parts to the test, which typically takes only 20-25 minutes. The first part involves the subject listening to different pitches and frequencies in order to determine what the ear is capable of hearing. The second part involves using headphones to test bone and air conduction, and the results from this part of the test will help determine where a problem lies, if one is found.
Pure tone audiometry test results are plotted on a graph called an audiogram. One side of the graph represents frequency or pitch, and the other represents intensity, or decibels (dB). The marks on the graph show the softest sound the person could hear at each frequency. Most common frequencies tested are 250, 500, 1000, 2000, 4000 and 8000 Hertz (Hz), each within a range of 0 to 120 dB.
The results of the tests give the pure-tone thresholds (PTT) of an individual, which represent the softest tones the person can hear at least half of the time. Test results are considered normal when the number is 0-25 dB, progressing to mild hearing loss at 26-40 dB, moderate at 41-55 dB, moderate-to-severe at 56-70 dB and severe at 71-90 dB. Hearing loss is considered severe when the number is more than 90 dB, and it is at this stage that speech and language begin to be affected. The test determines the softest sound for each frequency, so it can determine whether a person has a problem hearing only low- or high-frequency sounds and not just diagnose overall hearing difficulties.
A pure tone audiometry test can diagnose a number of problems. Age-related hearing loss, also known as presbycusis, can affect middle-age to elderly individuals and have a significant effect on their ability to hear higher frequencies and the spoken word. Otitis media is typically seen in young children and occurs when fluid begins to build up in the middle ear. When diagnosed early enough, measures can be taken to prevent further hearing loss. Pure tone audiometry can also diagnose noise-related hearing loss, which can occur at any age and is most frequently seen in individuals who are repeatedly exposed to the same noise, such as working around loud machinery without the proper ear protection.