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Audiology/Otolaryngology

Pure-Tone Audiometry

Hearing loss is a common condition that affects millions of people regardless of age, ethnicity, and health status. Appropriate treatment for hearing loss depends greatly on the underlying pathophysiology and the severity of the condition. Pure-tone audiometry is a critical means of obtaining diagnostic information to guide healthcare providers toward appropriate treatment. Appropriate treatment for hearing loss depends significantly on the pathophysiology and the severity of the condition, and

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  • When a sudden change in hearing is reported, immediate pure-tone evaluation is warranted to determine whether a significant hearing loss has occurred and if it meets the criteria for sudden sensorineural hearing loss (SSNHL).
  • Identification of SSNHL and rapid initiation of therapy is critical due to the limited time window for SSNHL treatment to be effective.
  • If a concern about hearing is not addressed, negative outcomes range from developmental delays to poorer quality of life to debilitating disability.
  • Pure-tone audiometry is a critical means of obtaining diagnostic information to guide healthcare providers toward appropriate treatment.
  • Pure-tone (isolated frequency) audiometry evaluation over the range of frequencies important for everyday listening can determine the degree, configuration, and type of hearing loss in a manner detailed enough to assist the healthcare team in determining the etiology and prognosis for the hearing loss as well as the optimal treatment strategy.
  • Pure-tone testing assesses the auditory system through 2 pathways.
  • In air conduction testing, sound waves enter the external auditory canal and pass through the tympanic membrane, ossicular chain, and cochlea to reach the cochlear nerve (part of cranial nerve VIII) and then travel through the brainstem to the auditory cortex.
  • In bone conduction testing, sound waves are introduced directly to the cochlea through the vibration of a bone conduction oscillator on the mastoid process.
  • By utilizing both methods of pure-tone testing, hearing loss is determined to be conductive (involving the pinna through the ossicular chain), sensorineural (involving the cochlea to the auditory cortex), or mixed (both conductive and sensorineural involvement).
  • Pure-tone evaluation should be performed for patients concerned about abnormal auditory perception, ear trauma, or otologic disease.
  • This includes but is not limited to, subjective hearing loss, tinnitus, hyperacusis, ototoxic monitoring protocols, dizziness or vertigo, middle ear dysfunction, traumatic brain injury or temporal bone fracture, loud noise exposure, blast injury, failed hearing screening, speech delay in children, or conditions with risk factors for hearing loss.
  • Pure-tone evaluation is typically performed in a sound-treated booth to reduce the impact of external sounds, with the booth environment and electroacoustic equipment calibrated to American National Standards Institute (ANSI) standards to optimize inter-test and intra-test reliability.
  • Standard electroacoustic transducers for pure-tone audiometry are supra-aural headphones, insert earphones, circumaural headphones, and bone conduction oscillators.
  • Results are recorded on a graph known as the audiogram, which logarithmically plots sound frequency in cycles per second (Hertz or Hz) from low pitch to high pitch along the X-axis and loudness in decibels of hearing level (dB HL) from soft to loud along a reversed Y-axis.
  • A common method of summarizing standard pure-tone audiometric findings is using the pure-tone average (PTA), the arithmetic mean of each ear's thresholds at 500, 1000, and 2000 Hz.
  • Hearing loss is generally categorized by the degree of difficulty detecting sound in 5 dB increments, from normal hearing sensitivity at ≤25 dB HL to mild (26 to 40 dB HL), moderate (41 to 55 dB HL), moderately severe (61 to 70 dB HL), severe (71 to 90 dB HL), or profound (91+ dB HL) hearing loss.
  • The pediatric cutoff for normal hearing sensitivity is ≤15 dB HL, with 20 and 25 dB HL categorized as slight hearing loss due to the higher need for sound access for appropriate development in children.
  • Once air conduction and bone conduction thresholds are determined, hearing loss is categorized as sensorineural if the frequencies falling outside normal limits have air conduction and bone conduction thresholds within 10 dB of each other.
  • The hearing loss is considered conductive if bone conduction is within normal limits, but at least 1 frequency has a difference between bone conduction and air conduction of ≥15 dB; the loss is described as "mixed" if there are some sensorineural loss frequencies and some conductive loss frequencies, or if the hearing loss has both conductive and sensorineural aspects in 1 or more frequencies.
  • The configuration of a hearing loss refers to the shape of the plotted audiogram, as some configurations are strongly correlated with specific causes of hearing loss, such as sloping high-frequency loss with presbycusis, notching mid-frequency loss with genetic causes or low-frequency hearing loss rising to normal hearing with cochlear hydrops (see Graph . Audiogram for Presbycusis).
  • A Stenger test may be used to assess for malingering in a unilateral or asymmetric hearing loss by observing how the patient responds to a pure tone presented simultaneously to both ears when 1 tone is easily audible in the better-hearing ear but is quieter than the apparent threshold in the ear with greater hearing loss.
  • In SSNHL, a hearing asymmetry is considered significant if there is a ≥30 dB difference over 3 consecutive frequencies.
  • Outside of sudden hearing loss, a significant threshold shift, according to the American Academy of Otolaryngology-Head and Neck Surgery, is ≥10 dB increase in the PTA, or at 3000, 4000, and 6000 Hz, in either ear; the Occupational Safety and Health Administration standards for a shift for noise-related hearing loss are an average of ≥10 dB threshold increases for 2, 3, and 4 kHz.
  • The American Speech-Language-Hearing Association considers a threshold shift significant for ototoxicity monitoring when there is a ≥20 dB threshold increase at a single frequency, ≥10 dB at 2 adjacent frequencies, or loss of response at 3 or more consecutive previously-obtained frequencies in the ultra-high frequency range where maximum volume outputs are limited.
  • Hearing asymmetry is a common symptom of retrocochlear pathologies, such as vestibular schwannoma (see Graph . Audiogram for Vestibular Schwannoma/Acoustic Neuroma).
  • The definition of a significant hearing asymmetry varies throughout the literature, but an asymmetry of ≥20 dB at 2 consecutive frequencies or ≥15 dB at 2 frequencies between 2,000 and 8,000 Hz should raise suspicion for retrocochlear pathology.
  • Aside from hearing deficits, pure-tone audiometry is utilized in the test battery to assess loudness discomfort levels, indicating hyperacusis when the discomfort threshold is ≤85 dB HL or softer.
  • Pure-tone thresholds also help determine the etiology of tinnitus, and pure-tone presentations are also used as part of pitch and loudness matching assessment for characterizing tinnitus handicaps and guiding auditory-based treatment for tinnitus.
Pure-tone average (PTA)
the arithmetic mean of each ear's thresholds at 500, 1000, and 2000 Hz.
  • Pure-tone audiometry is the standard gold method of determining the type, degree, and configuration of hearing loss due to its widespread availability, inter-test reliability, and relative ease of execution.
  • Pure-tone audiometry results provide context for diagnosis, reassurance, monitoring, or further investigation of ear concerns.
  • Repeated assessments track changes in hearing as an indicator of changes in ear health over time.
  • Pure-tone audiometry is a low-risk, low-cost procedure but can provide crucial information regarding differential diagnosis, symptom etiology or pathophysiology, and guidance for appropriate treatment.
  • Any time a hearing loss or abnormal auditory perception is reported as a symptom, a referral to audiology for testing that includes pure-tone evaluation should be part of the evaluation process.
  • A reliable pure-tone evaluation cannot be completed if a patient cannot provide reliable behavioral responses.
  • This is particularly true of children under 6 months of age but is also seen in patients with developmental delays or neurological impairment.
  • Behavioral pure-tone testing may also be contraindicated if unreliable responses are given by patients who are malingering or who have factitious disorders.
  • In these circumstances, objective electrophysiologic or otoacoustic emission testing instead of behavioral responses is necessary to build a complete clinical picture.
  • For some patients, a false "conductive" component may appear in the presence of "third-window" pathologies like semicircular canal dehiscence because of changes in sound transmission from the dehiscence.
  • Due to how sound transmits through the skull, a sufficiently loud presentation of air conduction or bone conduction to 1 ear may cross to the cochlea of the other ear to elicit a response, which may confuse audiometry results.
  • When an asymmetry between ears is present, or a conductive component is suspected, masking noise is introduced to the non-test ear (NTE) via air conduction to artificially raise that ear's threshold and prevent a response from that ear.
  • The minimum volume possible to overcome interaural attenuation is used to calculate when masking is necessary by comparing the questionable threshold of the test ear to the bone conduction threshold of the NTE for that frequency.
  • For bone conduction testing, the interaural attenuation is 0 dB, the supra-aural headphone interaural attenuation is 40 dB, and the insert earphone interaural attenuation is 55 dB.
  • A complete pure-tone assessment includes both bone and air conduction for the left and right ear, with masking completed as appropriate.
  • Otalgia, particularly of the pinna or auditory canal, may prevent the appropriate placement of headphones for air conduction.
  • Supra-aural headphones are necessary in cases of atresia, but when stenotic or partially occluded canals are involved, the pressure they apply may cause canal obstruction and introduce a false conductive component.
  • Insert earphones can prevent external auditory canals from collapsing during testing and reduce the incidence of masking dilemmas.
  • Additionally, due to the differences in calibration between inserted earphones and headphones, the larger cavity created by tympanostomy tubes can cause low-frequency thresholds to be falsely elevated when using inserted earphones.
  • Behavioral complications include false positive responses, which can result from confusing tinnitus with the presented tone, responding to a regular rhythm of tone presentation, or over-eagerness to "do well" on the evaluation, particularly when a "passing score" is required for employment qualification.
  • False negatives may occur when a patient does not provide consistent responses to audible tones due to a lack of understanding of testing procedures, a deficit in central processing, or a non-organic deficit caused by malingering or factitious disorders.
  • Pure-tone thresholds can vary slightly with different transducers and transducer placement or in patient alertness and attention variations.
  • In adults, standard diagnostic test-retest variability is typically ±5 dB across frequencies.
  • The pediatric population's test-retest variability may be as great as +/-10 dB.
  • A masking dilemma occurs when the amount of masking noise necessary to prevent sound crossover of a tone to the NTE is loud enough to cross back to the test ear and falsely elevate the evaluated threshold.
  • This occurs most commonly with severe bilateral conductive hearing loss.
  • Repeated assessments track changes in hearing as an indicator of changes in ear health over time.
  • The American Speech-Language-Hearing Association considers a threshold shift significant for ototoxicity monitoring when there is a ≥20 dB threshold increase at a single frequency, ≥10 dB at 2 adjacent frequencies, or loss of response at 3 or more consecutive previously-obtained frequencies in the ultra-high frequency range where maximum volume outputs are limited.
  • review
    Pure-Tone Audiometry. StatPearls [Internet] — Anja C. Carl, Marc H. Hohman, Jennifer Cornejo — StatPearls Publishing, 2023

Decision support only. Verify against local protocols and current labeling. Source: www.ncbi.nlm.nih.gov