What is a Pure-Tone Audiometry Test?
What is Pure-Tone Audiometry?
And Why is it So Common?
Regular testing and screening are essential to maintaining good aural health. While there is not yet a cure for most types of hearing loss, early detection can go a long way towards a better long-term prognosis. The most common type of hearing exam you'll likely encounter is known as pure-tone audiometry.
What is a Pure Tone?
In the context of audiology, a pure tone is a sound with only a single frequency and a uniform wavelength. Pure tones do not occur naturally, as even sounds that seem to be a single pitch frequently have multiple overtones and oscillating wavelengths. Because pure tones are always the same frequency, this makes them ideally suited to test for the presence of hearing loss.
How Does a Pure Tone Audiometry Test Work?
As the name implies, pure tone audiometry leverages pure tones to determine whether or not an individual may be suffering from hearing loss.
How they work is relatively simple. First, the patient is given a pair of high-quality headphones and placed in a specialized, soundproof booth. They are instructed to indicate when they are able to hear a sound, either through a gesture or by pressing a button.
The audiologist then emits a series of pure tones at various volumes and frequencies through the patient's headset. As noted by Science Direct, a typical pure tone test uses 1, 2, 4, and 8kHz tones, followed by 250 Hz and 500 Hz.
Each sound starts at a level well above the established hearing threshold, at which point it is reduced in 10 dB intervals until it is no longer audible. Once the patient can no longer hear the tone, the audiologist then increases its intensity by 5 dB intervals until it is once more audible.
A typical pure tone test measures each ear independently.
The results of a pure tone test, while highly subjective, give an audiologist an idea of the maximum and minimum threshold at which a patient can hear common frequencies. If these thresholds are outside the baseline, this may indicate the presence of hearing loss. The patient can perform pure tone tests online, though the results will generally be less accurate than if an audiologist carried it out.
How Are the Results of Pure Tone Audiometry Measured?
The audiogram generated by a pure tone test is used to assign a hearing threshold to the patient, ranging from normal hearing to total deafness. These thresholds are as follows:
Normal. The patient is able to hear all sounds above 20 dB.
Slight Hearing Impairment. The patient has difficulty hearing sounds below 40 dB.
Moderate Hearing Impairment. The patient has difficulty hearing sounds below 70 dB.
Severe hearing impairment. The patient has difficulty hearing sounds below 90 dB.
Profound hearing impairment. The patient has difficulty hearing sounds below 120 dB.
Total Deafness. Even sounds 120 dB or above cannot be heard by the patient.
For context, normal conversation is 60 dB. The sound of a lawnmower averages around 90 dB. Someone whispering 5 feet away typically registers as 20 dB.
Why is Pure Tone Audiometry So Common?
Pure tone audiometry is widely accepted as the gold standard for hearing exams, a highly-effective means of measuring hearing impairment. There are a few reasons for this.
High level of accuracy. Although there's bound to be some data variance given that the test relies on patient input, it's still one of the best ways to determine the presence of hearing impairment.
Ability to identify asymmetric vs. symmetric hearing loss. Tests are carried out for each ear individually.
Typically delivers results in under thirty minutes
Requires minimal equipment. Theoretically, all that's required for a pure tone test is a set of high-quality headphones. This also makes the test highly cost effective.
With that said, pure tone audiometry is not perfect. While it can determine the presence of hearing impairment, additional evaluation is necessary to drill down to specific causes or identify specific symptoms. It's still an invaluable tool in every audiologist's arsenal, mind you.
But it's at its best when augmented by other exams and evaluations.