On pure tone audiometry, the air-bone gap is the difference between air conduction and bone conduction thresholds. A maximal conductive hearing loss produces an air-bone gap of approximately:

• A 25 dB
• B 70 dB
• C 90 dB
• D 40–60 dB ✓

Explanation

A pure conductive hearing loss theoretically produces a maximum air-bone gap of approximately 60 dB (the gain provided by the middle ear sound-transformer mechanism). In clinical practice, maximum air-bone gap with complete middle ear ossicular discontinuity is ~55–60 dB. A 25 dB gap indicates mild conductive loss. In mixed hearing loss, both air conduction and bone conduction thresholds are elevated with a residual air-bone gap. Pure sensorineural loss has no air-bone gap (both thresholds equally elevated).

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.