As speech pathologists, it is well within our scope of practice to help families interpret and understand results of formal hearing evaluations, especially the details provided on an audiogram. First, I will define the measures used in formal hearing testing. Then, I will describe some symbols used on an audiogram. Finally, I will discuss the three different types of hearing loss.
Frequency and Decibels
Two measurements evaluate hearing: frequency and decibels. Frequency, also known as Hertz (Hz), denotes sound pitch, ranging from 250 Hz to 8000 Hz. An example of a low pitch would be the sound of thunder; for a midrange pitch, an example would be a telephone ring. A high pitch example would be the sound of cymbals clanging.
Decibels (dB) mean intensity or loudness; and it is measured from 0 dB through 110dB. Normal conversational speech is about 45 dB. It is important to note that 0dB does not mean the complete absence of sound, but rather it is the softest sound that a person with normal hearing ability would be able to detect at least 50% of the time.
We call the softest level at which your child can hear the threshold. In a hearing evaluation, an audiologist tests frequencies from low to high decibels until the client hears each pitch. The audiologist then documents the threshold for each frequency on the audio gram. When testing is completed with headphones, it is called “air” thresholds because the sound must travel through the air of the ear canal to be heard.
Audiogram Symbols
Your child’s audiogram should have a box explaining what the symbols used on the diagram represent. The right ear is marked with an O, and the left ear with an X to indicate air thresholds. When using bone conduction, the audiologist places a small device behind the child’s ear, secured by a metal band. This device sends sounds via direct vibration of the bone and specifically tests the sensitivity of the inner ear. A < symbol denotes the right ear and a > symbol indicates the left ear’s responses to bone conduction. If testing reveals a hearing loss, the audiologist will compare results of air and bone conduction testing to identify the type of loss.
Types of Hearing Loss
There are three kinds of hearing loss: conductive, sensorineural, and mixed. A conductive loss means the outer or middle parts of the ear are not working effectively. Fluid or wax build-up blocks sound from transferring to the intact inner ear. The audiologist confirms this because bone conduction testing showed an intact inner ear, but air conduction indicated a problem.
A conductive hearing is sometimes treatable with medication or surgery and is typically temporary. However, if your child is experiencing a conductive loss during peak learning opportunities, then you may notice limited responses to language and reduced verbalizations. While your child receives treatment, seize every chance to let them watch your lips form sounds and use visuals to aid understanding. Even with one affected ear, they perceive speech as if underwater.
A sensorineural loss occurs when the inner ear is not properly receiving sounds. Your child’s audiogram would indicate an air conduction threshold and bone conduction threshold with the same amount of hearing loss. Several factors cause this loss, including aging, prolonged exposure to loud noises, viral infections, disrupted blood supply to the ear, metabolic disturbances, accidents, and genetic predisposition. About 90% of people with hearing impairments have this type of loss. Regrettably, medications or surgeries cannot treat it, but hearing aids can enhance responses to sounds. Those with a severe hearing loss may benefit from a cochlear implant.
A mixed hearing loss is the combination of a conductive and sensorineural loss. In this case, your child may already have a sensorineural hearing loss and then develop a conductive loss due to excessive fluid or wax in the ears. In an audiogram, you would see bone conduction thresholds indicating a hearing loss and the air conduction thresholds showing an even greater hearing loss.
Ranges
The following indicates results for the average ADULT. It is harder to use the same interpretation with children as children may not respond well in testing for a variety of reasons, but these numbers should give you a general sense of severity levels.
- -10 dB to 25 dB = Normal range
- 26 dB to 40 dB = Mild hearing loss
- 41 dB to 55 dB = Moderate hearing loss
- 56 dB to 70 dB = Moderately Severe hearing loss
- 71 dB to 90 dB = Severe hearing loss
- over 90 dB = Profound hearing loss
Next Steps
After an evaluation using headphones in a sound-proof booth setting, your audiologist should be able to answer the following questions based on test results:
- How well does my child hear at low, medium, and high pitches?
- Does my child have a hearing loss?
- If my child has a hearing loss, what part of the ear is affected: outside, middle, or inner?
This article, including the diagram, originates from an Audiology Awareness Campaign article by Glen R. Meier, M.S., CCC-A, FAAA. For more details about audiological hearing evaluations, read my post: Why Does my Child need a Diagnostic Hearing Evaluation?
