How to Read an Audiogram
You just performed a pure tone audiometry test and your audiogram is in front of you – what now?
Now, it’s time to understand how to read an audiogram.
Audiometry is a key tool in uncovering, preventing or treating hearing loss. Let’s get back to basics with an indepth look at the audiogram, audiogram examples and some more information on how to read the results of a hearing test.
Pure tone audiometry results have significant influence on the diagnosis and treatment plan for patients. In occupational health audiometry can determine whether or not a patient is fit for work or should receive compensation due to hearing loss. While in a diagnostic audiometry setting decisions regarding surgery, hearing aid prescription or other medical treatments are based on the results found on the audiogram report.
Either way, being able to read an audiogram is crucial for any clinician involved in audiometric evaluation and it is certainly useful to refresh your knowledge from time to time.
So let’s do exactly that.
- Pure tone Audiometry
- Introduction to the audiogram
- Measuring Hearing loss
A hearing care professional will use an audiometer to conduct pure tone audiometry hearing test (air and bone conduction) as part of their audiological test battery. Pure tone audiometry is used to assess a hearing ability, specifically, the softest sounds that a patient can hear.
These are called hearing thresholds. In simple terms, a hearing threshold is the softest sound a person can hear at each frequency 50% of the time.
It is important to note that pure tone audiometry results yield quantitative information about one’s hearing. (Qualitative would indicate how well speech is heard and/or understood).
During testing, the audiometer presents pure tone sounds to the patient’s ear. These tones are played from low to high frequencies (Hz) at different intensity levels (dB).
Air conduction testing transmits pure tones to the outer ear (ear canal), which go through the middle ear and finally reach the inner ear. Hence, air conduction evaluates the whole hearing system.
Bone conduction pure tones are transmitted through the skull using a bone vibrator (oscillator) which is placed on the mastoid or forehead. Bone conduction stimulates and assesses the cochlea directly and bypasses the outer and middle ear.
The goal in testing is to produce an audiogram which is a representation of data collected in a hearing test.
An audiogram report is used to determine the following:
- The presence of hearing loss
- The type of hearing loss
- The configuration of hearing loss (which frequencies are specifically affected)
- The degree of hearing loss (the severity)
- Whether hearing loss is unilateral(one side) or bilateral (both sides).
Let’s get right into how to read an audiometry report.
What is an audiogram?
An audiogram is a graph that indicates a patient’s ability to hear. It shows low to high frequencies or pitch (Hz) on the horizontal axis and low to high intensities or volume (dB) on the vertical axis as can be seen on this blank audiogram.
Intensity is measured in decibels (dB) with -10 dB being the softest sound. Each horizontal line represents the increase in loudness of sound as the dB value increases.
Note: -10 dB does not mean that there is no sound, rather, it is the softest sound that an individual with ‘normal’ hearing is able to hear 50% of the time.
Frequency is measured in Hertz (Hz). The range of conventional audiometry begins from low pitch sound at 125 Hz (the sound of thunder or the “oo” sound in “who”), to high pitch sounds at 8000 Hz (the sound of violins, birds chirping or the “s” sound in “speech”)
The most important frequencies for speech we hear every day are in the 250 Hz to 6000 Hz range.
Note: While the conventional audiometry range peaks at 8000 Hz, ultra-high frequency audiometry peaks at 20000 Hz and is mostly used in early detection of ototoxic effects of treatment and early diagnosis of hearing loss.
There are various symbols used on audiometry graphs, but most clinicians refer to the widely used and recommended standard set of symbols (ASHA, 1990). These symbols are used to mark and describe information about the patient’s hearing give more detail about the test that was performed.
Common Audiogram Symbols
Note: The term ‘masked’ above refers to additional noise that was presented in the non-test ear. This is done to prevent the non-test ear from hearing the tones presented and “helping” the test ear to hear.
Symbols that pertain to the left ear are marked in blue and the right ear marked in red.
The standard measurement for degrees of hearing loss helps us understand the effect hearing loss may have. A common standard is the World Health Organisation (WHO) standard.
By obtaining air conduction hearing thresholds we are able to determine the degree of hearing loss and better understand its effects.
Below is a blank audiometry graph with degrees of hearing loss represented in coloured bands based on WHO standards.
[Generated at ‘hearingaidknow’.]
- Normal Hearing
- Mild Hearing Loss (26 – 40 dB HL)
Can hear conversation in quiet environments but will battle to hear in noisy environments.
- Moderate Hearing Loss (41- 55 dB HL)
Understands conversation in a quiet space when face to face, where the vocabulary is constrained to a known topic. May miss up to 70% of the conversational message.
- Moderately-Severe Hearing Loss (56- 70 dB HL)
Will struggle to hear normal conversation in a quiet room and miss most of the conversation content.
- Severe Hearing Loss (71 – 90 dB HL)
Can only hear communication when speech is loud. May not hear voices at all
- Profound Hearing Loss (90+ dB HL)
Will not hear conversation at, even if the speaker is shouting loud. May even perceive speech as vibrations.
The configuration of hearing loss is classified by the shape of the patient’s air conduction thresholds plotted on the audiometry graph across the frequency spectrum. Various shapes/configurations of the patient’s hearing loss may be associated with certain aetiologies of hearing loss.
For example; by nature, presbycusis or age related hearing loss, is typically sloping in shape and affects the higher frequencies first and more.
A commonly used system for configuring hearing loss is shown below. Please note that below the word octave will be used. Octave frequencies are the frequencies seen on the horizontal axis of the audiometry graph (250, 500, 1000, 2000, 4000 and 8000 Hz).
We have examined different methods of presenting the tone to the ear, which are air conduction (sound energy goes through the outer, middle then to the inner ear), and bone conduction (sound energy bypasses the outer and middle ear and goes directly to the inner ear).
Both air and bone conduction test results on the audiometry graph help us determine whether the problem or cause of hearing loss is in the outer, middle or inner ear.
There are three basic types of hearing loss.
If the air conduction threshold results show a loss of hearing, but the bone conduction threshold results are within normal limits, the hearing loss is conductive. This means that there is a problem either in the outer or middle ear as the conduction of sound from the earphone is being obstructed.
Wax impaction in the ear canal and otitis media with effusion are examples of the causes of conductive hearing loss.
Example of conductive hearing loss audiogram results (degree: mild) [sourced from Aussie Deaf Kids]
If both air and bone conduction testing threshold results show the same amount of hearing loss, then the hearing loss is sensorineural. This means that the problem is in the inner ear alone.
To explain further, there is no obstruction creating a ‘gap’ in the results, in the outer and middle ear. Sensorineural hearing loss can be caused by ototoxicity (drug related hearing loss) and noise induced hearing loss among others.
Example of a sensorineural hearing loss audiometry results (degree: mild to moderate) [sourced from Aussie Deaf Kids]
If both air and bone conduction threshold results show a hearing loss, BUT, the air conduction thresholds show a much worse hearing loss, then this is called a mixed hearing loss.
This means that the problem is in the outer and/or middle ear (conductive), AND the inner ear (sensorineural), therefore mixed.
Example of a mixed hearing loss audiometry results (degree: moderate to profound) [sourced from Aussie Deaf Kids]
By knowing how to read audiometry reports, a clinician is able to classify the hearing loss according to degree, configuration and type and use this information to determine the need for further diagnostic assessment and audiological management or to refer the patient for medical intervention.