During pure tone audiometry, the right ear shows an air conduction threshold of 65 dB HL at 1000 Hz and the left ear shows a threshold of 10 dB HL. What must be done to obtain a valid right ear air conduction threshold?
- A Repeat the test using insert earphones without any additional step
- B Mask the left (non-test) ear with narrow band noise before retesting the right ear ✓
- C Record the threshold as unreliable since cross-hearing cannot occur by air conduction
- D Increase the stimulus intensity until the patient responds and accept it as the true threshold
Correct answer: B. Mask the left (non-test) ear with narrow band noise before retesting the right ear
Explanation
When the gap between the test ear air conduction threshold and the non-test ear bone conduction threshold exceeds the interaural attenuation (about 40 dB for supra-aural earphones, higher for inserts), the stimulus crosses over via bone conduction and the non-test ear may respond. Narrow band noise delivered to the better ear prevents this shadow response. Option C is wrong because cross-hearing occurs readily by bone conduction even with air conduction stimulation.
Reference: Dhingra Diseases of Ear, Nose and Throat, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.