Interpretation of Investigations

Please note an audiologist/AVM/ENT will send a summary/copy of the basic investigations below to you after the assessment has taken place.


The British Society of Audiology produced a detailed procedure for ear examination.

Tuning Forks

Provides preliminary diagnostic information.


  • Comparison of air conduction (AC) and bone conduction (BC) sensitivity
  • Tuning fork is alternated between entrance of ear canal and mastoid process
  • Rinne Positive: Tuning fork is louder via AC= sensorineural hearing loss (SNHL)
  • Rinne Negative: Tuning fork is louder on mastoid= conductive hearing loss (CHL)


  • Test of lateralisation and therefore may be used for patients who report unilateral hearing loss.
  • The tuning fork is placed midline on the patients’ forehead.
  • If sound lateralises to ear with loss= CHL as the improved BC is due to the occlusion effect.
  • If soundlateralises to ear without loss=SNHL or mixed hearing loss (MHL) as the best cochlea is detecting the signal. In normal hearing= midline

Types of hearing loss

  • CHL is a result of dysfunction in the middle or outer ear (BC >AC)
  • SNHL is a result of cochlea damage (sensory) and/or neural (8th nerve) (BC = AC)
  • Mixed hearing loss is a combination of dysfunction in middle/outer ear and cochlea/8th nerve (A certain amount of AC and BC loss)
  • Central hearing loss refers to everything in the auditory cortex (Brain) whereas peripheral hearing loss is the result of everything before the brain (outer, middle, inner ear)

Interpreting a Pure-tone Audiogram (PTA)

  • An audiogram is a plot of frequency in Hertz (Hz) against intensity measured in decibels hearing level (dB HL). The frequency range for a PTA is 250 Hz to 8000Hz as this range of frequencies is similar to the range important for speech understanding.
  • The intensity ranges from -10dB HL to 120dB HL. Thresholds (lowest acoustic intensity perceived at a given frequency) for both the right and left ear are plotted based on the frequency. Refer to image below.
  • Masked AC/BC thresholds are an accurate assessment of the test ear.
  • Further interpretation and explanations on Pure-tone Audiogram are available on the BSA website:
Descriptor Average hearing threshold levels (dB HL)
Normal Hearing < 20
Mild hearing loss 21 - 40
Moderate hearing loss 41 - 70
Severe hearing loss 71 - 95
Profound hearing loss > 95

pure tone audiogram chart, right and left

Interpreting a Tympanogram

  • Tympanogram is graphic display of tympanic membrane compliance (ml or cm3) as a function of pressure changes in the external auditory meatus. See figure 1.

Image of tympanogram chart

  • Tympanometry is sensitive to middle ear effusion, cholesteatoma, ossicular adhesions, and space occupying lesions in contact with the eardrum, ossicular discontinuity, perforations and ear canal occlusions.
  • The shape of the tympanogram should also be described and simple descriptions such as ‘normal’, ‘rounded’, ‘flat’, ‘wide’ or ‘W-shaped’.
  • The BSA has further interpretation and explanations on Tympanometry.

Examples of Types of Hearing Loss

Conductive Hearing Loss

  • An audiogram illustrating a mild conductive hearing loss in the right ear. The air-conduction thresholds for the right ear are shown as O’s and the masked, bone-conduction thresholds are shown as brackets.

Image of a conductive hearing loss chart

  • Examples of a conductive hearing loss included a perforated tympanic membrane, and otitis media with effusion etc.

Sensorineural Hearing Loss

  • An audiogram illustrating a mild-moderate, high-frequency sensorineural hearing loss in the right ear.

Sensorineural Hearing loss chart

  • Examples of a SNHL includes presbycusis, an acoustic neuroma, Meniere’s disease, and noise-induced hearing loss etc.

Mixed hearing loss

  • An audiogram illustrating a moderate-to-severe, mixed hearing loss in the left ear. Both the air-conduction thresholds (X’s) and the bone-conduction thresholds (brackets) indicate hearing loss.

Mixed hearing loss chart

  • Examples of mixed hearing loss includes otosclerosis, a SNHL with a perforation/otitis media with effusion.


Stanley A. Gelfand (2011). Essentials of Audiology, 3rd Edition. Thieme, New York NY 2011