Pure Tone Audiometry: Audiogram Interpretation and Hearing Loss Classification — Cost, Top Hospitals & Success Rates | MyMedicPlus

Pure tone audiometry (PTA) is the gold-standard subjective behavioural test for measuring hearing sensitivity across a range of frequencies. It determines the hearing threshold level (HTL) — the lowest intensity at which a pure tone can be reliably detected by the patient — at standardised frequencies from 250 Hz to 8000 Hz, and sometimes extended to 12,500 Hz or 16,000 Hz for high-frequency audiometry. Results are plotted on an audiogram, a graph with frequency (Hz) on the horizontal axis and hearing level in decibels hearing level (dB HL) on the vertical axis (higher dB HL = poorer hearing).

PTA tests two pathways of sound transmission:

• Air conduction (AC): Sound delivered through calibrated insert earphones or circumaural (supra-aural) headphones. The AC pathway tests the entire peripheral auditory system — outer ear, middle ear, cochlea, and auditory nerve.
• Bone conduction (BC): A bone oscillator is placed on the mastoid process (or forehead for mid-line placement). Vibration bypasses the outer and middle ear and directly stimulates the cochlea and auditory nerve. BC testing isolates inner ear function.

The difference between AC and BC thresholds — the air-bone gap (ABG) — is the key diagnostic parameter:

• No air-bone gap (AC = BC), both elevated: Sensorineural hearing loss (SNHL) — cochlear or retrocochlear pathology
• Air-bone gap present (AC worse than BC by ≥10 dB at two or more frequencies): Conductive hearing loss — outer or middle ear pathology
• Both AC and BC elevated, with air-bone gap: Mixed hearing loss — combined conductive and sensorineural components

PTA is performed by a registered audiologist or trained ENT technician in a sound-treated booth conforming to ISO 8253-1 standards (maximum permissible ambient noise levels). The test is fully subjective — it depends on the patient's reliable responses — distinguishing it from objective tests such as otoacoustic emissions (OAE) or auditory brainstem response (ABR).

PTA characterises the type, degree, and configuration of hearing loss, guiding diagnosis of a wide range of otological and systemic conditions:

Sensorineural hearing loss (SNHL) — AC and BC both elevated, no ABG:

• Age-related hearing loss (presbycusis): Bilateral symmetrical high-frequency SNHL, gradually sloping from 2000-8000 Hz; the most common cause of adult-onset hearing loss worldwide
• Noise-induced hearing loss (NIHL): Characteristic audiogram notch at 4000 Hz (occasionally 3000 or 6000 Hz) with relative preservation of speech frequencies; caused by acoustic trauma from industrial noise or recreational noise (firearms, concerts)
• Sudden sensorineural hearing loss (SSHL): Unilateral hearing loss of ≥30 dB across three consecutive frequencies, arising within 72 hours; audiological emergency requiring urgent imaging and treatment
• Ototoxicity: High-frequency SNHL or pan-frequency loss from cisplatin, aminoglycosides (gentamicin), loop diuretics (furosemide), or quinine
• Meniere's disease: Fluctuating low-frequency SNHL in early stages, progressing to flat or all-frequency loss; associated with episodic vertigo and tinnitus
• Acoustic neuroma (vestibular schwannoma): Unilateral progressive SNHL, often with disproportionate impairment of speech discrimination relative to pure tone average — a "rollover" phenomenon on PI-PB function curve

Conductive hearing loss — air-bone gap present, BC normal or near-normal:

• Otosclerosis (see Carhart notch below), chronic otitis media with effusion (glue ear), tympanic membrane perforation, ossicular chain disruption, external auditory canal atresia or stenosis, cerumen impaction

Mixed hearing loss: Combined features — typically chronic suppurative otitis media with secondary cochlear damage, or otosclerosis with advanced sensorineural component.

PTA is indicated for any patient in whom a hearing disorder is suspected, whether arising from symptoms, occupational screening, or as part of a structured diagnostic pathway:

Symptomatic indications:

• Patient-reported hearing difficulty in quiet or noisy environments, difficulty following speech, or asking for repetition of words
• Tinnitus (unilateral or bilateral) — PTA establishes associated hearing loss configuration and guides management
• Otalgia, otorrhoea, or ear fullness with potential hearing component
• History of head trauma, blast injury, barotrauma, or acoustic trauma
• Dizziness or vertigo when Meniere's disease or other endolymphatic disorders are suspected
• Family history of hereditary hearing loss (connexin 26/GJB2, Waardenburg syndrome, Usher syndrome)

Screening programmes:

• Newborn hearing screening (NHS programme in the UK, EHDI in the US): PTA is not used in neonates (automated OAE and ABR are used at that age); PTA becomes the primary confirmatory test from approximately 3-4 years
• Occupational health screening: Annual audiometry for workers exposed to >85 dB(A) daily noise exposure (COSHH regulations in the UK; OSHA standards in the US)
• Pre-employment audiometry for aviation, military, and specific industrial occupations
• Ototoxicity monitoring: Baseline and serial PTA for patients receiving cisplatin chemotherapy, aminoglycoside antibiotics, or other potentially ototoxic agents

Pre-operative and post-operative assessment:

• Before middle ear surgery (myringoplasty, ossiculoplasty, stapedectomy): baseline audiogram documents pre-operative hearing status and guides surgical target
• After middle ear surgery: PTA at 6-8 weeks to quantify air-bone gap closure and evaluate surgical outcome
• Before cochlear implant assessment in patients with severe-to-profound SNHL

PTA is unsuitable for infants and young children who cannot provide reliable voluntary responses; age-appropriate alternatives (visual reinforcement audiometry, play audiometry, ABR) are used until the child is developmentally ready for standard PTA, typically age 4-5 years.

PTA is performed using a standardised protocol (ISO 8253-1, BSA recommended procedures) with specific technical requirements for masking and threshold determination:

Threshold determination method:

• The Hughson-Westlake 'up 5, down 10' bracketing method is the standard: Tones are presented in 10 dB steps downward (toward threshold) and 5 dB steps upward (away from threshold) until the patient responds to 50% of presentations at a given level — defined as the threshold. A minimum of two responses at the same intensity constitutes a reliable threshold.
• Standard test frequencies: 250, 500, 1000, 2000, 4000, 8000 Hz; inter-octave frequencies (750, 1500, 3000, 6000 Hz) added when the threshold difference between adjacent octave frequencies exceeds 20 dB.

Masking (essential for valid bilateral assessment):

• When testing one ear, sound may cross the skull via bone conduction and be detected by the non-test ear (cross-hearing). This artefact — the 'shadow curve' — produces falsely elevated thresholds in the non-test ear.
• Masking: Narrowband noise is delivered to the non-test ear during AC and BC testing whenever the interaural attenuation threshold is exceeded. Rules govern when and how much masking to apply (minimum masking, plateau/Hood method).
• Under-masking produces false thresholds; over-masking elevates true thresholds. Accurate masking is the most technically demanding aspect of clinical PTA.

Hearing loss classification (WHO and BSA):

• Normal: 0-25 dB HL (adults); 0-15 dB HL in children (ASHA criteria)
• Mild: 26-40 dB HL — difficulty hearing soft speech, whispers; may miss consonants in noisy environments
• Moderate: 41-55 dB HL — difficulty hearing conversational speech; hearing aids strongly indicated
• Moderately severe: 56-70 dB HL — requires significant amplification; considerable communication difficulty
• Severe: 71-90 dB HL — can hear only loud speech or environmental sounds; powerful hearing aids or cochlear implant candidacy
• Profound: >90 dB HL — minimal or no useful residual hearing; cochlear implant candidacy assessment

The Carhart notch (otosclerosis): A characteristic dip in bone conduction thresholds at 2000 Hz (typically 5-15 dB below adjacent BC frequencies) in patients with stapes fixation (otosclerosis). This notch is a mechanical artefact of the bony cochlear capsule resonance being altered by the fixed stapes footplate — it does not reflect true sensorineural damage and resolves after successful stapedectomy. Its presence is a key audiological clue to the diagnosis of otosclerosis on a background of conductive hearing loss with a large ABG at low-to-mid frequencies.

PTA provides unique and irreplaceable information in the audiological diagnostic pathway:

Comprehensive frequency-specific threshold mapping: Unlike tuning fork tests, which give only broad impressions of laterality and type of hearing loss, PTA quantifies precise thresholds at each frequency, enabling accurate hearing aid prescription, cochlear implant candidacy assessment, and monitoring of disease progression or treatment response.

Differentiates conductive from sensorineural loss: The air-bone gap calculation — which requires both AC and BC thresholds — is the only hearing test capable of identifying the site of lesion within the peripheral auditory system. This directs the treatment pathway: conductive losses are often surgically correctable (grommets, myringoplasty, ossiculoplasty, stapedectomy), while SNHL requires amplification or cochlear implantation.

Provides diagnostic audiogram patterns:

• 4 kHz notch: Noise-induced hearing loss
• Carhart notch at 2 kHz BC: Otosclerosis
• Low-frequency SNHL fluctuating over serial tests: Meniere's disease
• Flat profound SNHL: Connexin 26 mutation, advanced NIHL, meningitis-related hearing loss
• Asymmetric SNHL: Always requires MRI of internal auditory meati to exclude acoustic neuroma

Medicolegal and occupational documentation: PTA is the legally required baseline and surveillance tool for occupational noise-induced hearing loss claims. Serial audiograms document threshold shifts attributable to workplace exposure and are used in noise-at-work litigation and compensation assessments in most jurisdictions.

Cost-effectiveness: PTA is inexpensive, non-invasive, and rapid (30-60 minutes). Its combination with basic tympanometry and speech audiometry in a standard test battery provides a highly cost-effective comprehensive hearing assessment requiring no anaesthesia or radiation.

PTA is a subjective test dependent on patient cooperation, accurate audiologist technique, and calibrated equipment. The following limitations must be recognised:

Patient-related limitations:

• Subjective response variability: Patients who are anxious, cognitively impaired, very young, or uncooperative may provide inconsistent responses. Threshold variability of ±5-10 dB between test sessions is normal; greater variability requires repeat testing or objective corroboration with ABR.
• Non-organic (functional) hearing loss: Some patients deliberately or subconsciously respond inconsistently to obtain compensation or secondary gain. Stenger test (for unilateral non-organic loss), ABR, and ASSR provide objective cross-checks.
• Fatigue: Testing elderly or ill patients requires rest breaks; auditory fatigue from prolonged exposure to test tones at suprathreshold levels can temporarily depress thresholds (temporary threshold shift).

Technical limitations:

• Equipment calibration: Audiometers must be calibrated annually (ISO 8253 and ANSI S3.6) against reference equivalent sound pressure levels. Drift in calibration causes systematic threshold errors.
• Ambient noise: Testing outside an ISO-compliant sound-treated booth allows background noise to mask test tones at low intensities (250 Hz most affected), elevating apparent thresholds. Maximum permissible ambient noise levels are specified by ISO 8253-1.
• Masking errors: Failure to apply adequate masking produces shadow curves and false unilateral hearing loss patterns; over-masking elevates true thresholds by cross-masking the test ear.

Test ceiling and floor: Standard clinical audiometers test to 120 dB HL maximum (some to 110 dB HL). Patients with profound losses may not respond even at maximum output, precluding threshold measurement. ABR or ASSR must be used for these patients.

PTA results direct a structured clinical pathway based on the type, degree, and configuration of hearing loss identified:

Speech audiometry (SRT and discrimination scores):

• Speech reception threshold (SRT): The intensity level at which the patient correctly identifies 50% of spondaic words (two-syllable equal-stress words: "baseball," "hotdog"). The SRT should agree with the pure tone average (PTA) at 500, 1000, 2000 Hz within ±10 dB — a wider discrepancy suggests non-organic hearing loss or retrocochlear pathology.
• Speech discrimination score (WRS/PB max): Percentage of monosyllabic phonetically balanced (PB) words correctly identified at a suprathreshold level (typically PTA + 30-40 dB). Scores: ≥90% excellent; 76-90% good; 60-75% fair; <60% poor — suggesting retrocochlear pathology (acoustic neuroma), severe SNHL, or central auditory processing disorder.

Tuning fork tests (clinical correlation):

• Rinne test: 512 Hz tuning fork placed on mastoid (BC), then in front of ear canal (AC). Positive Rinne (AC > BC) = normal or SNHL; Negative Rinne (BC > AC) = conductive loss of >25 dB ABG (or false negative Rinne in dead ear — SNHL so severe that masking must exclude cross-hearing).
• Weber test: 512 Hz fork placed on vertex of skull. Lateral to poorer ear = conductive loss in that ear; lateral to better ear = SNHL in the opposite (poorer) ear; midline = symmetrical thresholds or normal.

Management by hearing loss type:

• Conductive HL: Refer to ENT for surgical assessment (grommets for OME, myringoplasty for perforation, stapedectomy for otosclerosis, ossiculoplasty for ossicular chain disruption)
• SNHL, mild-moderate: Hearing aid assessment; NHS provision in UK; commercial audiological services with digital BTE, RIC, or ITE devices. CROS/BiCROS aids for unilateral profound SNHL.
• SNHL, severe-profound: Cochlear implant assessment (CI candidacy criteria: aided speech discrimination <50% in best-aided condition; threshold >70-90 dB HL across key frequencies); bone-anchored hearing aids (BAHA/Osia) for conductive or mixed HL not amenable to surgery.

Pure tone audiometry is among the most cost-effective diagnostic tests in medicine. Costs vary by setting (hospital, private audiology clinic, community hearing centre) and country:

Consultation and test costs:

• Standard PTA with tympanometry and speech audiometry: USD 75-300 in private audiology settings in the US and UK; free or subsidised through NHS (UK), Medicare (Australia), or national health programmes
• Paediatric audiological assessment (play audiometry, VRA, plus PTA when age-appropriate): USD 150-500 including paediatric audiologist time
• Industrial/occupational audiometry: USD 50-150 per employee through occupational health providers; bulk discount programmes available for employers

Cost of hearing aids (triggered by PTA diagnosis):

• NHS hearing aids (UK): Free of charge for eligible patients with confirmed hearing loss on PTA
• Private digital hearing aids: USD 1,000-4,000 per aid; bilateral fitting USD 2,000-8,000; rechargeable RIC (receiver-in-canal) devices in the mid-tier provide excellent speech performance
• OTC hearing aids (FDA-regulated in US from 2022): USD 200-1,000 per pair; suitable for mild-moderate loss in adults aged ≥18

Cochlear implantation costs (for profound SNHL diagnosed by PTA pathway):

• USD 50,000-100,000 per ear in the US (device + surgery + programming + rehabilitation)
• India: USD 8,000-15,000 per ear (device + surgery) — substantially lower due to reduced operative costs; rehabilitation and mapping costs additional
• Covered by NHS in the UK and most European national health systems for eligible candidates

Importance of early diagnosis: Hearing loss identified by PTA in infancy (through paediatric audiological pathways) and fitted with amplification before 6 months has significantly better language and educational outcomes than late-identified children, justifying robust national newborn hearing screening programmes and rapid audiological follow-up.

PTA is the primary audiological test but is supplemented by or replaced with objective tests in specific clinical situations:

• Otoacoustic emissions (OAE): Objective test of outer hair cell function. Transient evoked OAE (TEOAE) and distortion product OAE (DPOAE) require no patient response and are the standard newborn hearing screening tool. OAEs are absent when cochlear hearing loss exceeds approximately 30-35 dB HL but cannot provide frequency-specific thresholds. Used as a quick screen and to differentiate cochlear from retrocochlear pathology (OAEs present in retrocochlear disorders despite elevated PTA thresholds).
• Auditory brainstem response (ABR / BAER): Objective electrophysiological test measuring neural responses from cochlea to brainstem. Click-ABR assesses high-frequency cochlear function and is used for retrocochlear screening (acoustic neuroma). Tone-burst ABR provides frequency-specific threshold estimation for infants too young for PTA. ABR is not affected by patient cooperation or sedation level.
• Auditory steady-state response (ASSR): Frequency-specific electrophysiological test capable of estimating thresholds at multiple frequencies simultaneously; particularly useful for estimating degree of profound hearing loss above audiometer output limits for cochlear implant candidacy assessment.
• Tympanometry (impedance audiometry): Measures middle ear compliance and pressure; identifies tympanic membrane perforations, middle ear effusion (type B flat tympanogram), Eustachian tube dysfunction, and discontinuity of the ossicular chain. Always performed alongside PTA in a standard hearing assessment battery.
• Visual reinforcement audiometry (VRA) and play audiometry: Behavioural adaptations of standard audiometry for children aged 6 months to 5 years who cannot participate in conventional PTA.

No single test replaces PTA for the complete frequency-specific characterisation of hearing threshold in a cooperative adult or older child. The recommended assessment battery — PTA + tympanometry + speech audiometry + OAE — provides complementary information that together enables confident diagnosis and appropriate management planning.