What does an air-bone gap on an audiogram show?

An air-bone gap on an audiogram indicates the presence of conductive hearing loss.1

This gap represents a significant difference between the thresholds measured via air conduction and bone conduction. While air-conduction testing measures sound traveling through the outer and middle ear to the cochlea, bone-conduction testing stimulates the cochlea directly through the skull, bypassing the outer and middle ear.21

When a conductive defect—such as otosclerosis or another middle ear condition—is present, the air-conduction threshold is poorer than the bone-conduction threshold. Consequently, the air-bone gap serves as a measure of the loss in transmission across the middle ear and indicates the maximum potential hearing improvement that may be achieved through successful corrective surgery.12