Air-conduction and bone-conduction reference threshold levels-A multicenter studya)

Air-conduction (AC) and bone-conduction (BC) thresholds were measured to evaluate standard reference thresholds and recommend revisions to audiometer standards. AC and BC thresholds were measured from listeners with normal hearing (NH) and sensorineural hearing loss (SNHL) at three sites. NH participants (n = 53) were selected based on age (18-25 years old), normal AC thresholds, tympanometry, otoscopy, and absence of otologic disease. SNHL participants (n = 49) were selected based on AC thresholds, tympanometry, otoscopy, and absence of otologic disease. AC thresholds obtained from NH listeners averaged 3.7 dB hearing level (HL). Air-bone gaps (ABGs) occurred in NH and SNHL listeners above 2000 Hz and in SNHL listeners at 250 Hz. Corrections to standard reference equivalent threshold sound pressure levels are recommended. ABGs in listeners without conductive pathology result from incorrect reference threshold levels for frequencies above 2000 Hz. False ABGs increase with hearing-loss magnitude, probably the result of the effects of ambient and internal noise for low-level BC stimuli. False ABGs place patients at risk for unnecessary medical and surgical intervention. Reference threshold levels should achieve two objectives: (1) AC thresholds from young NH listeners should average 0 dB HL; and (2) ABGs from listeners with normal middle-ear function should average 0 dB.