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Interpreting hearing tests

A hearing assessment is a set of tests that check each other. Here is what each one measures, what it cannot, and how they combine into a diagnosis.

Audiogram Pure-tone audiogram showing air conduction thresholds around 40 to 50 decibels and bone conduction thresholds around 10 to 25 decibels. The shaded area between them is the air-bone gap. 0 20 40 60 80 100 120 250 500 1k 2k 4k 8k Frequency (Hz) Hearing level (dB HL) <<<<< air-bone gap
Air conduction <Bone conduction Air-bone gap

Pure-tone audiometry

The audiogram: thresholds for tones at each frequency, by air and by bone, for each ear. It classifies the loss as conductive, sensorineural or mixed and quantifies it. Its reliability depends on masking and on the person’s cooperation; it is a behavioural test.

Speech audiometry

Word and sentence recognition at set levels. It checks that the pure-tone result is plausible (the speech threshold should match the pure-tone average), quantifies clarity, and predicts how much a device can help. A word score that is worse than the audiogram suggests looks beyond the middle ear.

Tympanometry

A probe in the ear canal varies air pressure and measures how much sound the eardrum reflects. The result is a curve:

  • Type A — normal peak: normal middle-ear pressure and compliance.
  • As — shallow peak: a stiff system, as in otosclerosis or tympanosclerosis.
  • Ad — very high peak: a floppy system, as in ossicular discontinuity or a thin drum.
  • B — flat: fluid, a perforation (large volume) or wax (small volume).
  • C — negative pressure: Eustachian-tube dysfunction.

It takes seconds and it distinguishes causes of conductive loss that the audiogram cannot.

Acoustic (stapedial) reflexes

A loud tone makes the stapedius muscle contract and stiffens the chain, which the probe detects. The reflex is absent in stapes fixation, ossicular discontinuity and significant conductive loss, and in severe sensorineural loss. It is present in a third-window lesion despite an air-bone gap — the single most useful discriminator between otosclerosis and canal dehiscence before imaging.

Otoacoustic emissions and evoked potentials

Emissions test outer hair cell function and are useful in children and in suspected non-organic loss; they are absent with any significant conductive loss. Auditory brainstem responses test the nerve and pathway and are used when a retrocochlear cause is suspected or when behavioural testing is not possible.

Imaging

Not part of every assessment. CT of the temporal bone shows bone: ossicles, otosclerotic foci, cholesteatoma extent, canal dehiscence, prosthesis position. MRI shows soft tissue and fluid: the nerve and inner ear, tumours, residual cholesteatoma on diffusion imaging. Order imaging to answer a question, not as routine.

Putting it together before surgery

Air-bone gap + normal drum + absent reflexes + As tympanogram + Carhart notch: stapes fixation likely; CT optional. Air-bone gap + normal drum + present reflexes + supranormal low-frequency BC: third window until proven otherwise; CT with superior canal reformats and VEMPs mandatory before any stapes surgery. Large flat gap + Ad tympanogram: discontinuity. Gap with type B and large canal volume: perforation. Poor word recognition disproportionate to PTA: look retrocochlear and set expectations. Asymmetric SNHL: MRI. Speech thresholds discordant with PTA: repeat audiometry before believing either.

This page provides general educational information. It cannot replace an individual assessment, which depends on a full history, examination, audiometry and, where relevant, imaging. If you have sudden hearing loss, severe pain, facial weakness, severe dizziness or discharge with fever, seek medical care promptly.