Pure-tone audiometry: how to read an audiogram
- Examination
The audiogram plots the faintest tone heard at each pitch, by air and by bone; its shape gives the type, degree and often the cause of hearing loss.
What it is
Pure-tone audiometry is a behavioural test: the patient presses a button for the faintest tones heard at each frequency. Air conduction is tested through earphones and bone conduction through a vibrator on the mastoid, with masking noise in the other ear when needed. The chart shows frequency (low to high, left to right) against hearing level in decibels (louder further down). Comparing air and bone lines tells whether the loss is conductive, sensorineural or mixed; the shape of the curve points to noise, ageing, Ménière disease or otosclerosis. Speech audiometry completes it.
Findings and interpretation
- Degree is described as mild, moderate, moderately severe, severe or profound; WHO uses the better-ear average to judge disability.
- Conductive: bone conduction normal, air worse, air–bone gap (wax, effusion, perforation, otosclerosis).
- Sensorineural: air and bone equally reduced, no gap (ageing, noise, ototoxic drugs, Ménière disease, genetic causes, vestibular schwannoma).
- Otosclerosis: conductive loss with a normal eardrum; a dip in bone conduction near 2000 Hz (Carhart notch) is classic but not specific.
- Word recognition is near normal in conductive loss once sound is loud enough, reduced in cochlear loss and worst in neural loss.
- Sudden sensorineural loss: at least 30 dB in three connected frequencies within 72 hours; a medical emergency.
How it is done
- Do otoscopy first and remove wax; test in a quiet booth and tell the patient to respond to every tone, even very faint ones.
- Air conduction with headphones or insert earphones, better ear first, across the frequencies from 250 to 8000 Hz.
- Find each threshold by bracketing the level up and down until the faintest tone the patient detects reliably.
- Bone conduction with a vibrator on the mastoid, up to 4000 Hz.
- Mask the non-test ear with noise whenever cross-hearing is possible, always for bone conduction when ears differ.
- Speech audiometry: speech reception threshold (should agree with the average at 500, 1000 and 2000 Hz) and word recognition score.
- Read the chart: O and X for right and left air conduction, < and > for bone; then name the type, degree, shape and symmetry.
Audiogram patterns
| Pattern | Air conduction | Bone conduction | Typical causes |
|---|---|---|---|
| Conductive | Raised thresholds | Normal (air–bone gap) | Wax, effusion, perforation, otosclerosis |
| Sensorineural | Raised thresholds | Raised equally (no gap) | Presbycusis, noise, ototoxic drugs, Ménière disease, vestibular schwannoma |
| Mixed | Raised more | Raised, with a gap on top | Chronic otitis media, advanced otosclerosis |
| Noise notch | Dip at 3–6 kHz, deepest near 4 kHz, recovery at 8 kHz | Same dip | Occupational or recreational noise |
| Presbycusis | High frequencies worst, sloping down, both ears | Same as air | Ageing |
| Ménière disease (early) | Low frequencies, one ear, fluctuating | Same as air | Endolymphatic hydrops |
Common mistakes
- Reading air conduction alone: without bone conduction and masking, a loss cannot be called conductive or sensorineural.
- Overlooking the difference between the ears: an asymmetric sensorineural loss needs imaging even if the patient only complains of tinnitus.
- Assuming a normal audiogram means normal hearing: adults who hear tones but do not understand speech need speech and central auditory testing.
Next step / Initial management
- Read the audiogram with otoscopy and tympanometry; a conductive loss with a normal drum and a normal or shallow tympanogram points to otosclerosis (routine ENT referral).
- Sudden sensorineural loss: refer the same day; corticosteroids work best when started early and help less after 2 to 4 weeks.
- Asymmetric sensorineural loss, poor word recognition or neurological signs: priority referral to ENT for gadolinium-enhanced MRI of the internal auditory canals.
- Bilateral presbycusis or noise loss: routine referral to audiology for hearing aids (cochlear implants for severe to profound loss); noise-exposed workers need annual audiometry and hearing protection.
Test yourself
Think of the answer, then tap the question to see it.
The left ear shows bone conduction at 10 dB and air conduction at 45 dB across all frequencies. What type of loss is this?
Left conductive hearing loss: a 35 dB air–bone gap with normal bone conduction.
A factory worker has a bilateral dip at 4 kHz with better hearing at 8 kHz. What is the likely cause?
Noise-induced hearing loss (the noise notch).
Which audiometric criterion defines sudden sensorineural hearing loss?
A loss of at least 30 dB in three connected frequencies developing within 72 hours.
A 50-year-old has a one-sided sensorineural loss with poor word recognition. What study comes next?
Gadolinium-enhanced MRI of the internal auditory canals to look for a vestibular schwannoma.
Connections
Educational content; it does not replace a medical assessment and is not a clinical instruction. For a real case, follow current guidelines and specialist advice.
Sources: Hearing Loss (MSD Manual Professional Edition, 2026); Deafness and hearing loss (fact sheet) (World Health Organization, 2026); Sudden Deafness (NIDCD, National Institutes of Health, 2018); Understand Noise Exposure (CDC, National Institute for Occupational Safety and Health, 2026); Age-Related Hearing Loss (Presbycusis) (NIDCD, National Institutes of Health, 2023).
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Representative model, for educational purposes only.