What is the role of pure tone audiometry (PTA) in diagnosing and managing hearing loss in patients of all ages?

Pure Tone Audiometry in Diagnosing and Managing Hearing Loss

Pure tone audiometry (PTA) is the gold standard diagnostic test for hearing loss across all age groups and should be the primary objective assessment method when hearing impairment is suspected. 1, 2, 3

Core Diagnostic Role

PTA serves as the foundation for hearing loss evaluation by:

• Establishing the type of hearing loss (conductive, sensorineural, or mixed) through air and bone conduction threshold measurements 1, 2
• Quantifying the degree of hearing loss using standardized classifications: normal (≤20 dB HL), mild (21-40 dB HL), moderate (41-55 dB HL), moderately severe (56-70 dB HL), severe (71-90 dB HL), and profound (>90 dB HL) 2
• Determining the frequency-specific pattern of hearing loss, which guides treatment decisions and helps identify underlying pathology 1, 2

Essential Testing Components

A comprehensive audiometric evaluation must include:

• Pure tone thresholds at 250-8000 Hz, including mid-octave frequencies (3000 and 6000 Hz) with additional inter-octaves as appropriate 1
• Both air and bone conduction measurements to differentiate conductive from sensorineural components 1, 2
• Speech audiometry including speech recognition threshold (SRT) and word recognition scores (WRS) to assess functional hearing ability 1, 2
• Tympanometry to evaluate middle ear function 4, 1
• Otoacoustic emissions (OAEs) to determine cochlear outer hair cell function 4, 1

The speech-critical frequency range of 500-4000 Hz is particularly important for understanding conversation and should receive special attention during interpretation. 2

Age-Specific Testing Approaches

Testing methodology must be adapted to patient age:

• Infants under 6 months: Auditory brainstem response (ABR) and OAEs 2
• Children 6 months to 2 years: Visual reinforcement audiometry 4, 2
• Children 2-5 years: Conditioned play audiometry 4, 2
• Children ≥5 years and adults: Conventional pure tone audiometry 4, 2

For children, normal hearing is defined as ≤15 dB HL at the 3-frequency pure tone average (500,1000,2000 Hz), recognizing that children under age 3 may have thresholds up to 15 dB greater than older children due to developmental factors. 2

Critical Clinical Flags Requiring Further Evaluation

Asymmetric hearing loss (difference in PTA between ears >15 dB or difference >15% in word recognition scores) warrants immediate referral to an otolaryngologist and imaging studies to rule out retrocochlear pathology such as vestibular schwannoma. 1, 5, 3

Additional red flags include:

• Conductive or mixed hearing loss patterns requiring otolaryngologic evaluation 1, 5
• Poor word recognition scores disproportionate to pure tone thresholds 1, 5
• Sudden sensorineural hearing loss requiring urgent corticosteroid therapy if within 2 weeks of onset 5
• Lightheadedness with hearing loss suggesting Ménière's disease (requires confirmation of low to mid-frequency sensorineural hearing loss) 1

Monitoring and Serial Testing

PTA plays a crucial role in longitudinal monitoring:

• Baseline audiometry before ototoxic medications (cisplatin, aminoglycosides) with serial monitoring during and after treatment 4, 2
• Standard test-retest variability is typically ±5 dB across frequencies, so changes <10 dB may not represent true threshold shifts 2, 6
• Follow-up testing at 3-6 month intervals for persistent symptoms until resolution or additional intervention is needed 1
• Hearing function may deteriorate over time after platinum-based chemotherapy or cranial radiotherapy, though some patients remain stable or improve 4

Treatment Planning Based on PTA Results

PTA results directly guide intervention:

• Mild to moderate hearing loss: Hearing aids are first-line management and can be obtained over-the-counter for cost savings 5, 3
• Severe to profound bilateral hearing loss: Cochlear implantation should be considered when hearing aids provide insufficient benefit 4, 5
• Serviceable hearing (Class B: PTA 31-50 dB with discrimination 50-69%; Class C: PTA >50 dB with discrimination 50-69%) indicates hearing aids are appropriate and beneficial 2

Important Limitations and Pitfalls

Do not rely on tuning fork tests alone for clinical screening, as they lack sufficient accuracy compared to PTA. 1

Other critical considerations:

• PTA is a subjective test requiring patient cooperation, though it is highly reliable when properly performed 6
• Access limitations exist with 56.6% of US counties lacking audiologists 2
• Older adults may have difficulty completing testing due to cognitive dysfunction 2
• Age-specific reference values must be used when interpreting results, as hearing thresholds naturally deteriorate with age, particularly at high frequencies 2, 6
• Self-reported hearing loss using questionnaires has moderate accuracy (AUC 0.70-0.73 for mild hearing loss) but cannot substitute for audiometry in individual patient diagnosis 7

Integration with Other Diagnostic Modalities

While PTA is the gold standard, it should be complemented by:

• Auditory brainstem response to assess cochlear, auditory nerve, and lower brainstem function, though PTA detects more abnormalities than ABR 4
• MRI of brain and internal auditory canals as the imaging study of choice for asymmetric or unilateral sensorineural hearing loss 5
• Acoustic reflex testing to assess neural pathways 2