Tuesday, May 22, 2012

How to Read an Audiogram

As we enter into the final weeks of speech, language, and hearing month, I would like to focus on a hearing topic: understanding an audiogram. First, I will define the measures used in formal hearing testing. Next, I will describe some symbols used on an audiogram. Finally, I will discuss the three different types of hearing loss.

There are two measurements used to evaluate hearing: frequency and decibels.  Frequency, which is also known as Hertz and abbreviated Hz, refers to the pitch of a sound.  Frequencies are charted from a low pitch of 250 Hz through the highest pitch of 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.  The softest level at which your child can hear is called the threshold.  During a hearing evaluation, an audiologist presents low through high frequencies starting at the lowest decibel and increasing to higher decibels until the client demonstrates that he or she has heard the 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.
Your child's audiogram should have a box explaining what the symbols used on the diagram represent. An O is used for the right ear, and an X is used for the left ear to show air thresholds.  If bone conduction is used, you will see the audiologist place a small device just behind your child's ear which is held in place by a metal band that stretches over the top of the head.  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 a hearing loss is identified in testing, the audiologist will compare results of air and bone conduction testing to determine what kind of loss is present.

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.  Sound gets blocked from being transferred to the intact inner ear due to fluid or wax build-up.  The audiologist confirms this because bone conduction testing showed an intact inner ear, but air conduction indicated a problem.  A conductive hearing loss is 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 is being treated, you should take every opportunity you can to let your child watch your lips form sounds and use visuals like pointing to help your child follow directions.  Even if only one ear is affected, your child hears your speech on that side as though he or she is swimming 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.  There are several causes for this loss including but not limited to: aging, prolonged exposure to loud noises, viral infections, and disrupted blood supply to the ear, metabolic disturbances, accidents, and genetic predisposition.  About 90% of people with hearing impairments have this type of loss.  Unfortunately, it cannot be treated with medications or surgeries, but hearing aids can be helpful in improving 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.
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.
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?

Information, including the diagram in this article, was obtained from an article written by Glen R. Meier, M.S., CCC-A, FAAA as part of an Audiology Awareness Campaign.




5 comments:

  1. Hi! Is there a way you could email me this chart? I would love to have it posted in my room! Thanks so much,
    Kristin Cummings
    kcummingsslp@yahoo.com
    www.kcummingsslp.blogspot.com

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  2. This is a GREAT, SIMPLE, CONCISE explanation of audiograms and hearing testing! Love it!

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    Replies
    1. Thank you for your feedback! I originally wrote this post while reviewing information for my sister because she was, like many others, overwhelmed by interpreting the test for her daughter. It has proven to become one of my most popular posts! ASHA even pinned it to their board;)

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  3. Thanks for this! It is simplified and easy to understand.

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