Audiogram Interpretation for GP Registrars
An audiogram records the results of pure tone hearing tests. There are several common patterns on the audiogram.
An audiogram plots the softest sound that can be heard across a range of low to high pitch sounds. It graphs frequency (from low to high pitch sounds) against hearing threshold (volume of sound, from soft to loud volume).
There are commonly accepted ranges for normal, mild, moderate, severe and profound hearing loss. In adults, normal hearing is often 0-25 dB. Note that the baseline (0 dB) represents normal hearing, not the absence of sound completely.
The results are plotted with different symbols for air conduction in the right (O) and left (X) ears, +/- bone conduction in the right ([) and left (]) ears. Here is an example of a normal audiogram:
Conductive hearing loss. There is a mild loss of air conduction in both ears, but bone conduction is still normal.
Sensorineural hearing loss. Air and bone conduction are both equally abnormal.
Mixed hearing loss. There is a gap between air and bone conduction, but neither is normal.
Otitis media. There is a bilateral conductive hearing loss – air conduction is reduced but bone conduction is still normal.
Presbycusis, or age related hearing loss. There is downsloping symmetrical hearing loss, worse at higher frequencies.
Noise-induced hearing loss (industrial deafness). There is a notch around 4000 Hz. The patient may not understand speech well, as they are likely to miss the high frequency consonants of speech.
Perforation. There is a mild unilateral conductive loss. Earwax might give a similar conductive loss, but may also be likely to be bilateral.
Meniere disease. There is asymmetric unilateral hearing loss, upward sloping (worst in low frequencies).
Ototoxicity, such as gentamicin or cisplatin / carboplatin. There is a symmetrical downsloping sensorineural loss.
Otosclerosis. Early otosclerosis gives a bilateral mild-moderate conductive loss, greater in lower frequencies. There is a 2000 Hz Carhart notch in bone conduction. Late otosclerosis may give a mixed pattern.
Exercise: Can you identify these patterns?
Exercise: Which of the following are true?
- The X-axis represents pitch.
Yes, the x axis of the audiogram is the pitch (frequency) of the sound tested, with deep sounds on the left and high sounds on the right (like looking at a piano keyboard).
- Hearing threshold is measured in decibels (dB).
Yes, the softest volume that a person can hear (at least 50% of the time) is recorded on the audiogram and it is measured in decibels.
- O = left ear air conduction
No, O = right ear air conduction.
- X = right ear bone conduction
No, X = left ear air conduction.
- [ = right ear bone conduction
Yes, [ = right ear bone conduction.
- ] = left ear air conduction
No, ] = left ear bone conduction.
- 0 dB on the y axis is absolute silence.
No, 0 dB is the baseline threshold for normal hearing. Some patients can have hearing that is above this level, ie they can hear sounds that are even quieter than normal (such as -10 dB).
- Middle ear effusions cause a conductive loss.
Yes, middle ear effusions will affect air conduction but bone conduction may still be normal.
- Presbycusis affects high sounds more than low.
Yes, presbycusis (age-related hearing loss) affects the higher frequencies most.
December 18, 2016
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