A patient with bilateral asymmetric hearing loss undergoes pure-tone audiometry. When testing the left ear with 60 dB HL air-conduction at 1000 Hz, the right (non-test) ear has a bone-conduction threshold of 5 dB HL at the same frequency, and the interaural attenuation for the audiometer headphone is 40 dB. What is the minimum effective masking level required for the right ear?

• A 100 dB HL
• B 65 dB HL
• C 45 dB HL
• D 25 dB HL ✓

Explanation

The need to mask the non-test ear arises when the test signal (60 dB) minus interaural attenuation (40 dB) exceeds the bone-conduction threshold of the non-test ear (5 dB). The crossover signal reaching the non-test ear is 60 - 40 = 25 dB, which is above its BC threshold of 5 dB, so the right ear would be responding. Minimum effective masking = 25 dB HL. The formula for initial masking: test ear AC threshold - IA + 10 dB gives a starting level, but minimum effective masking equals the crossover signal level.

Reference: Katz Handbook of Clinical Audiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.