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Reading the pure tone audiogram
A pure tone audiogram of the left ear shows bone conduction thresholds at 5 to 10 dB across all frequencies, and air conduction thresholds at 45 to 50 dB. The right ear is normal throughout. What does this show, and what is the air-bone gap?
- correctA. Left conductive hearing loss, with a gap of about 40 dB
- B. Normal hearing bilaterally, with no significant gap
- C. Left mixed hearing loss, with a gap of about 10 dB
- D. Left sensorineural hearing loss, with a gap of about 40 dB
Explanation
Key fact
Normal bone conduction with impaired air conduction is a conductive loss. The gap between the two curves measures it.
Left conductive hearing loss, gap about 40 dB. The cochlea is working; the sound is not reaching it.
Why
Bone conduction bypasses the outer and middle ear and tests the cochlea.
It is normal here, so the inner ear and nerve are intact.
Air conduction tests the whole pathway, and it is impaired.
The difference between them is the air-bone gap.
Roughly 48 minus 8 gives about 40 dB.
Reading an audiogram: the gap between the two curves
Why not the others
- B. Normal hearing bilaterally, with no significant gap — ignores air conduction thresholds of 45 to 50 dB, which represent a moderate loss.
- C. Left mixed hearing loss, with a gap of about 10 dB — would need bone conduction to be impaired as well. It is normal here.
- D. Left sensorineural hearing loss, with a gap of about 40 dB — is self-contradictory. In sensorineural loss both curves fall together and there is no gap.
Remember
Bone normal, air down: the problem is before the cochlea.
Go deeper
The tuning fork result in the source recall follows the same arithmetic: Rinne turns negative at 256 Hz with a gap over about 15 dB, at 512 Hz over about 30, and at 1024 Hz over about 45 - so negative at the first two and positive at the third places the gap between 30 and 45 dB.
Otosclerosis classically shows the Carhart notch, a dip in bone conduction around 2000 Hz that resolves after successful stapedectomy.
A conductive loss of this size with an intact drum should prompt tympanometry, which separates effusion from ossicular fixation.
Dhingra PL, Dhingra S. Diseases of Ear, Nose and Throat, 9th ed. (Elsevier, 2025).